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The Low R, high C circuit is shown feeding a short vertical antenna, such as would be the case for a compact, mobile antenna or otherwise on frequencies below an antenna's lowest natural resonant frequency. Here the inherent capacitance of a short, random wire antenna is so high that the L-network is best realized with two inductors, instead of aggravating the problem by using a capacitor.
The Low R, high L circuit is shown feeding a small loop antenna. Below resonance this type of antenna has so much inductance, that more inductance from adding a coil would make the reactance even worse. Therefore, the L-network is composed of two capacitors.
An L-network is the simplest circuit that will achieve the desired transformation; for any one given antenna and frequency, once a circuit is selected from the eight possible configurations (of which six are shown above) only one set of component values will match the in impedance to the out impedance. In contrast, the circuits described below all have three or more components, and hence have many more choices for inductance and capacitance that will produce an impedance match. The radio operator must experiment, test, and use judgement to choose among the many adjustments that produce the same impedance match.
Antenna system losses
Loss in Antenna tuners
Every means of impedance match will introduce some power loss. This will vary from a few percent for a transformer with a ferrite core, to 50% or more for a complex ATU that is improperly tuned or working at the limits of its tuning range.
With the narrow band tuners, the L-network has the lowest loss, partly because it has the fewest components, but mainly because it necessarily operates at the lowest possible for a given impedance transformation. With the L-network, the loaded is not adjustable, but is fixed midway between the source and load impedances. Since most of the loss in practical tuners will be in the coil, choosing either the low-pass or high-pass network may reduce the loss somewhat. | Antenna tuner | Wikipedia | 430 | 582127 | https://en.wikipedia.org/wiki/Antenna%20tuner | Technology | Broadcasting | null |
The L-network using only capacitors will have the lowest loss, but this network only works where the load impedance is very inductive, making it a good choice for a small loop antenna. Inductive impedance also occurs with straight-wire antennas used at frequencies slightly above a resonant frequency, where the antenna is too long – for example, between a quarter and a half wave long at the operating frequency. However, problematic straight-wire antennas are typically too short for the frequency in use.
With the high-pass T-network, the loss in the tuner can vary from a few percent – if tuned for lowest loss – to over 50% if the tuner is not properly adjusted. Using the maximum available capacitance will give less loss, than if one simply tunes for a match without regard for the settings. This is because using more capacitance means using fewer inductor turns, and the loss is mainly in the inductor.
With the SPC tuner the losses will be somewhat higher than with the T-network, since the added capacitance across the inductor will shunt some reactive current to ground which must be cancelled by additional current in the inductor. The trade-off is that the effective inductance of the coil is increased, thus allowing operation at lower frequencies than would otherwise be possible.
If additional filtering is desired, the inductor can be deliberately set to larger values, thus providing a partial band pass effect. Either the high-pass T, low-pass π, or the SPC tuner can be adjusted in this manner. The additional attenuation at harmonic frequencies can be increased significantly with only a small percentage of additional loss at the tuned frequency.
When adjusted for minimum loss, the SPC tuner will have better harmonic rejection than the high-pass T due to its internal tank circuit. Either type is capable of good harmonic rejection if a small additional loss is acceptable. The low-pass π has exceptional harmonic attenuation at any setting, including the lowest-loss. | Antenna tuner | Wikipedia | 424 | 582127 | https://en.wikipedia.org/wiki/Antenna%20tuner | Technology | Broadcasting | null |
ATU location
An ATU will be inserted somewhere along the line connecting the radio transmitter or receiver to the antenna. The antenna feedpoint is usually high in the air (for example, a dipole antenna) or far away (for example, an end-fed random wire antenna). A transmission line, or feedline, must carry the signal between the transmitter and the antenna. The ATU can be placed anywhere along the feedline: at the transmitter, at the antenna, or somewhere in between.
Antenna tuning is best done as close to the antenna as possible to minimize loss, increase bandwidth, and reduce voltage and current on the transmission line. Also, when the information being transmitted has frequency components whose wavelength is a significant fraction of the electrical length of the feed line, distortion of the transmitted information will occur if there are standing waves on the line. Analog TV and FM stereo broadcasts are affected in this way. For those modes, matching at the antenna is required.
When possible, an automatic or remotely-controlled tuner in a weather-proof case at or near the antenna is convenient and makes for an efficient system. With such a tuner, it is possible to match a wide range of antennas (including stealth antennas).SGC World: Smart Tuners for Stealth Antennas.
When the ATU must be located near the radio for convenient adjustment, any significant SWR will increase the loss in the feedline. For that reason, when using an ATU at the transmitter, low-loss, high-impedance feedline is a great advantage (open-wire line, for example). A short length of low-loss coaxial line is acceptable, but with longer lossy lines the additional loss due to SWR becomes very high.
It is very important to remember that when matching the transmitter to the line, as is done when the ATU is near the transmitter, there is no change in the SWR in the feedline. The backlash currents reflected from the antenna are retro-reflected by the ATU – usually several times between the two – and so are invisible on the transmitter-side of the ATU. The result of the multiple reflections is compounded loss, higher voltage or higher currents, and narrowed bandwidth, none of which can be corrected by the ATU.
Standing wave ratio | Antenna tuner | Wikipedia | 466 | 582127 | https://en.wikipedia.org/wiki/Antenna%20tuner | Technology | Broadcasting | null |
It is a common misconception that a high standing wave ratio (SWR) per se causes loss. A well-adjusted ATU feeding an antenna through a low-loss line may have only a small percentage of additional loss compared with an intrinsically matched antenna, even with a high SWR (4:1, for example). An ATU sitting beside the transmitter just re-reflects energy reflected from the antenna ("backlash current") back yet again along the feedline to the antenna ("retro-reflection"). High losses arise from RF resistance in the feedline and antenna, and those multiple reflections due to high SWR cause feedline losses to be compounded.
Using low-loss, high-impedance feedline with an ATU results in very little loss, even with multiple reflections. However, if the feedline-antenna combination is 'lossy' then an identical high SWR may lose a considerable fraction of the transmitter's power output. High impedance lines – such as most parallel-wire lines – carry power mostly as high voltage rather than high current, and current alone determines the power lost to line resistance. So despite high SWR, very little power is lost in high-impedance line compared low-impedance line – typical coaxial cable, for example. For that reason, radio operators can be more casual about using tuners with high-impedance feedline.
Without an ATU, the SWR from a mismatched antenna and feedline can present an improper load to the transmitter, causing distortion and loss of power or efficiency with heating and/or burning of the output stage components. Modern solid state transmitters will automatically reduce power when high SWR is detected, so some solid-state power stages only produce weak signals if the SWR rises above 1.5 to 1. Were it not for that problem, even the losses from an SWR of 2:1 could be tolerated, since only 11 percent of transmitted power would be reflected and 89 percent sent out through to the antenna. So the main loss of output power with high SWR is due to the transmitter "backing off" its output when challenged with backlash current. | Antenna tuner | Wikipedia | 443 | 582127 | https://en.wikipedia.org/wiki/Antenna%20tuner | Technology | Broadcasting | null |
Tube transmitters and amplifiers usually have an adjustable output network that can feed mismatched loads up to perhaps 3:1 SWR without trouble. In effect the built-in π-network of the transmitter output stage acts as an ATU. Further, since tubes are electrically robust (even though mechanically fragile), tube-based circuits can tolerate very high backlash current without damage.
Broadcast Applications
AM broadcast transmitters
One of the oldest applications for antenna tuners is in AM and shortwave broadcasting transmitters. AM transmitters usually use a vertical antenna (tower) which can be from 0.20 to 0.68 wavelengths long. At the base of the tower an ATU is used to match the antenna to the 50 Ohm transmission line from the transmitter. The most commonly used circuit is a T-network, using two series inductors with a shunt capacitor between them. When multiple towers are used the ATU network may also provide for a phase adjustment so that the currents in each tower can be phased relative to the others to produce a desired pattern. These patterns are often required by law to include nulls in directions that could produce interference as well as to increase the signal in the target area. Adjustment of the ATUs in a multitower array is a complex and time consuming process requiring considerable expertise.
High-power shortwave transmitters
For International Shortwave (50 kW and above), frequent antenna tuning is done as part of frequency changes which may be required on a seasonal or even a daily basis. Modern shortwave transmitters typically include built-in impedance-matching circuitry for SWR up to 2:1 , and can adjust their output impedance within 15 seconds.
The matching networks in transmitters sometimes incorporate a balun or an external one can be installed at the transmitter in order to feed a balanced line. Balanced transmission lines of 300 Ohms or more were more-or-less standard for all shortwave transmitters and antennas in the past, even by amateurs. Most shortwave broadcasters have continued to use high-impedance feeds even before the advent of automatic impedance matching. | Antenna tuner | Wikipedia | 418 | 582127 | https://en.wikipedia.org/wiki/Antenna%20tuner | Technology | Broadcasting | null |
The most commonly used shortwave antennas for international broadcasting are the
HRS antenna (curtain array), which cover a 2 to 1 frequency range and the log-periodic antenna which cover up to 8 to 1 frequency range. Within that range, the SWR will vary, but is usually kept below 1.7 to 1 – within the range of SWR that can be tuned by antenna matching built-into many modern transmitters. Hence, when feeding these antennas, a modern transmitter will be able to tune itself as needed to match at any frequency.
Automatic antenna tuning
Automatic antenna tuning is used in flagship mobile phones, transceivers for amateur radio, and in land mobile, marine, and tactical HF radio transceivers.
Each antenna tuning system (AT) shown in the figure has an "antenna port", which is directly or indirectly coupled to an antenna, and another port, referred to as "radio port" (or as "user port"), for transmitting and / or receiving radio signals through the AT and the antenna. Each AT shown in the figure has a single antenna-port, (SAP) AT, but a multiple antenna-port (MAP) AT may be needed for MIMO radio transmission.
Several control schemes can be used in a radio transceiver or transmitter to automatically adjust an antenna tuner (AT).
The control schemes are based on one of the two configurations, (a) and (b), shown in the diagram. For both configurations, the transmitter comprises:
antenna
antenna tuner / matching network (AT)
sensing unit (SU)
control unit (CU)
transmitter and signal processing unit (TSPU)
The TSPU incorporates all the parts of the transmitting not otherwise shown in the diagram.
The TX port of the TSPU delivers a test signal. The SU delivers, to the TSPU, one or more output signals indicating the response to the test signal, one or more electrical variables (such as voltage, current, incident or forward voltage, etc.). The response sensed at the radio port in the case of configuration (a) or at the antenna port'' in the case of configuration (b). Note that neither configuration (a) nor (b) is ideal, since the line between the antenna and the AT attenuates SWR; response to a test signal is most accurately tested at or near the antenna feedpoint. | Antenna tuner | Wikipedia | 484 | 582127 | https://en.wikipedia.org/wiki/Antenna%20tuner | Technology | Broadcasting | null |
{| style="text-align:center;" class="wikitable"
|+ '''
|- style="vertical-align:bottom;"
! Control scheme !! Configuration !! Extremum-seeking?
|-
| Type 0 || n/a || n/a
|-
| Type 1 || (a) || No
|-
| Type 2 || (a) || Yes
|-
| Type 3 || (b) || No
|-
| Type 4 || (b) || Yes
|}
Broydé & Clavelier (2020) distinguish five types of antenna tuner control schemes, as follows:
Type 0 designates the open-loop AT control schemes that do not use any SU, the adjustment being typically only based on previous knowledge programmed for each operating frequency
Type 1 and type 2 control schemes use configuration (a)
type 2 uses extremum-seeking control
type 1 does not seek an extreme
Type 3 and type 4 control schemes use configuration (b)
type 4 uses extremum-seeking control
type 3 does not seek an extreme
The control schemes may be compared as regards:
use of closed-loop or open-loop control (or both)
measurements used
ability to mitigate the effects of the electromagnetic characteristics of the surroundings
aim / goal
accuracy and speed
dependence on use of a particular model of AT or CU | Antenna tuner | Wikipedia | 284 | 582127 | https://en.wikipedia.org/wiki/Antenna%20tuner | Technology | Broadcasting | null |
Wakefulness is a daily recurring brain state and state of consciousness in which an individual is conscious and engages in coherent cognitive and behavioral responses to the external world.
Being awake is the opposite of being asleep, in which most external inputs to the brain are excluded from neural processing.
Effects upon the brain
The longer the brain has been awake, the greater the synchronous firing rates of cerebral cortex neurons. After sustained periods of sleep, both the speed and synchronicity of the neurons firing are shown to decrease.
Another effect of wakefulness is the reduction of glycogen held in the astrocytes, which supply energy to the neurons. Studies have shown that one of sleep's underlying functions is to replenish this glycogen energy source.
Maintenance by the brain
Wakefulness is produced by a complex interaction between multiple neurotransmitter systems arising in the brainstem and ascending through the midbrain, hypothalamus, thalamus and basal forebrain.<ref></</ref> The posterior hypothalamus plays a key role in the maintenance of the cortical activation that underlies wakefulness. Several systems originating in this part of the brain control the shift from wakefulness into sleep and sleep into wakefulness. Histamine neurons in the tuberomammillary nucleus and nearby adjacent posterior hypothalamus project to the entire brain and are the most wake-selective system so far identified in the brain. Another key system is that provided by the orexins (also known as hypocretins) projecting neurons. These exist in areas adjacent to histamine neurons and like them project widely to most brain areas and associate with arousal. Orexin deficiency has been identified as responsible for narcolepsy.
Research suggests that orexin and histamine neurons play distinct, but complementary roles in controlling wakefulness with orexin being more involved with wakeful behavior and histamine with cognition and activation of cortical EEG.
It has been suggested the fetus is not awake, with wakefulness occurring in the newborn due to the stress of being born and the associated activation of the locus coeruleus. | Wakefulness | Wikipedia | 445 | 582180 | https://en.wikipedia.org/wiki/Wakefulness | Biology and health sciences | Ethology | Biology |
Oogenesis () or ovogenesis is the differentiation of the ovum (egg cell) into a cell competent to further develop when fertilized. It is developed from the primary oocyte by maturation. Oogenesis is initiated in the embryonic stage.
Oogenesis in non-human mammals
In mammals, the first part of oogenesis starts in the germinal epithelium, which gives rise to the development of ovarian follicles, the functional unit of the ovary.
Oogenesis consists of several sub-processes: oocytogenesis, ootidogenesis, and finally maturation to form an ovum (oogenesis proper). Folliculogenesis is a separate sub-process that accompanies and supports all three oogenetic sub-processes.
Oogonium —(Oocytogenesis)—> Primary Oocyte —(Meiosis I)—> First Polar body (Discarded afterward) + Secondary oocyte —(Meiosis II)—> Second Polar Body (Discarded afterward) + Ovum
Oocyte meiosis, important to all animal life cycles yet unlike all other instances of animal cell division, occurs completely without the aid of spindle-coordinating centrosomes.
The creation of oogonia
The creation of oogonia traditionally does not belong to oogenesis proper, but, instead, to the common process of gametogenesis, which, in the female human, begins with the processes of folliculogenesis, oocytogenesis, and ootidogenesis. Oogonia enter meiosis during embryonic development, becoming oocytes. Meiosis begins with DNA replication and meiotic crossing over. It then stops in early prophase.
Maintenance of meiotic arrest
Mammalian oocytes are maintained in meiotic prophase arrest for a very long time—months in mice, years in humans. Initially, the arrest is due to lack of sufficient cell cycle proteins to allow meiotic progression. However, as the oocyte grows, these proteins are synthesized, and meiotic arrest becomes dependent on cyclic AMP. The cyclic AMP is generated by the oocyte by adenylyl cyclase in the oocyte membrane. The adenylyl cyclase is kept active by a constitutively active G-protein-coupled receptor known as GPR3 and a G-protein, Gs, also present in the oocyte membrane. | Oogenesis | Wikipedia | 508 | 582473 | https://en.wikipedia.org/wiki/Oogenesis | Biology and health sciences | Animal reproduction | Biology |
Maintenance of meiotic arrest also depends on the presence of a multilayered complex of cells, known as a follicle, that surrounds the oocyte. Removal of the oocyte from the follicle causes meiosis to progress in the oocyte. The cells that comprise the follicle, known as granulosa cells, are connected to each other by proteins known as gap junctions, that allow small molecules to pass between the cells. The granulosa cells produce a small molecule, cyclic GMP, that diffuses into the oocyte through the gap junctions. In the oocyte, cyclic GMP prevents the breakdown of cyclic AMP by the phosphodiesterase PDE3, and thus maintains meiotic arrest. The cyclic GMP is produced by the guanylyl cyclase NPR2.
Reinitiation of meiosis and stimulation of ovulation by luteinizing hormone
As follicles grow, they acquire receptors for luteinizing hormone, a pituitary hormone that reinitiates meiosis in the oocyte and causes ovulation of a fertilizable egg. Luteinizing hormone acts on receptors in the outer layers of granulosa cells of the follicle, causing a decrease in cyclic GMP in the granulosa cells. Because the granulosa cells and oocyte are connected by gap junctions, cyclic GMP also decreases in the oocyte, causing meiosis to resume. Meiosis then proceeds to second metaphase, where it pauses again until fertilization. Luteinizing hormone also stimulates gene expression leading to ovulation.
Human oogenesis
Oogenesis
Oogenesis starts with the process of developing primary oocytes, which occurs via the transformation of oogonia into primary [oocyte]s, a process called oocytogenesis. From one single oogonium, only one mature oocyte will rise, with 3 other cells called polar bodies. Oocytogenesis is complete either before or shortly after birth. | Oogenesis | Wikipedia | 422 | 582473 | https://en.wikipedia.org/wiki/Oogenesis | Biology and health sciences | Animal reproduction | Biology |
Number of primary oocytes
It is commonly believed that, when oocytogenesis is complete, no additional primary oocytes are created, in contrast to the male process of spermatogenesis, where gametocytes are continuously created. In other words, primary oocytes reach their maximum development at ~20 weeks of gestational age, when approximately seven million primary oocytes have been created; however, at birth, this number has already been reduced to approximately 1-2 million per ovary. At puberty, the number of oocytes decreases even more to reach about 60,000 to 80,000 per ovary, and only about 500 mature oocytes will be produced during a woman's life, the others will undergo atresia (degeneration). Two publications have challenged the belief that a finite number of oocytes are set around the time of birth generation in adult mammalian ovaries by putative germ cells in bone marrow and peripheral blood. The renewal of ovarian follicles from germline stem cells (originating from bone marrow and peripheral blood) has been reported in the postnatal mouse ovary. In contrast, DNA clock measurements do not indicate ongoing oogenesis during human females' lifetimes.
Thus, further experiments are required to determine the true dynamics of small follicle formation.
Ootidogenesis
The succeeding phase of ootidogenesis occurs when the primary oocyte develops into an ootid. This is achieved by the process of meiosis. In fact, a primary oocyte is, by its biological definition, a cell whose primary function is to divide by the process of meiosis.
However, although this process begins at prenatal age, it stops at prophase I. In late fetal life, all oocytes, still primary oocytes, have halted at this stage of development, called the dictyate. After menarche, these cells then continue to develop, although only a few do so every menstrual cycle. | Oogenesis | Wikipedia | 410 | 582473 | https://en.wikipedia.org/wiki/Oogenesis | Biology and health sciences | Animal reproduction | Biology |
Meiosis I
Meiosis I of ootidogenesis begins during embryonic development, but halts in the diplotene stage of prophase I until puberty. The mouse oocyte in the dictyate (prolonged diplotene) stage actively repairs DNA damage, whereas DNA repair is not detectable in the pre-dictyate (leptotene, zygotene and pachytene) stages of meiosis. For those primary oocytes that continue to develop in each menstrual cycle, however, synapsis occurs and tetrads form, enabling chromosomal crossover to occur. As a result of meiosis I, the primary oocyte has now developed into the secondary oocyte.
Meiosis II
Immediately after meiosis I, the haploid secondary oocyte initiates meiosis II. However, this process is also halted at the metaphase II stage until fertilization, if such should ever occur. If the egg is not fertilized, it is disintegrated and released (menstruation) and the secondary oocyte does not complete meiosis II (and does not become an ovum). When meiosis II has completed, an ootid and another polar body have now been created. The polar body is small in size.
Ovarian cycle
The ovarian cycle is divided into several phases: | Oogenesis | Wikipedia | 293 | 582473 | https://en.wikipedia.org/wiki/Oogenesis | Biology and health sciences | Animal reproduction | Biology |
Follicologenesis: Synchronously with ootidogenesis, the ovarian follicle surrounding the ootid has developed from a primordial follicle to a preovulatory one. The primary follicle takes four months to become a preantral, two months to become antral, and then passes to a mature (Graaf) follicle. The primary follicle has oocyte-lining cells that go from floor to cubic and begin to proliferate, increasing the metabolic activity of the oocyte and follicular cells, which release glycoproteins and proteoglycans acids that will form the zona pellucida, which accompany the installation. In the preantral secondary follicle, internal and external theca cells begin to form. Aromatase, produced by follicular cells, transforms androgens produced by the inner theca into estrogens under the stimulation of FSH. LH stimulates theca cells to produce androgens. In the antral follicle, there is an antrum containing a follicle liquor, which contains estrogen, to allow the passage from the antral follicle to the Graaf follicle. The follicular antrum moves the oocyte and becomes eccentric; the oocyte is always surrounded by the pellucid zone and by follicular cells that form the oophorus cumulus. The innermost ones are called radiated corona cells. At this stage, the oocyte produces cortical granules containing acid glycoproteins.
Dominant follicle selection: The follicle with more FSH receptors will be more favored, simultaneously inducing the death of the other follicles (3-10 antral follicles that enter this phase each month). Low concentration estrogen will inhibit further production of FSH by the pituitary gland with negative feedback, so the follicles left behind will accumulate in the follicular antrum instead of androgens. | Oogenesis | Wikipedia | 432 | 582473 | https://en.wikipedia.org/wiki/Oogenesis | Biology and health sciences | Animal reproduction | Biology |
Graaf follicle: Estrogen at other concentrations induces LH release, with the peak of LH called LH surge, which induces stages that will lead to follicle burst. LH receptors also appear on follicular cells, which stimulate the oocyte to become a secondary oocyte, blocked in metaphase, waiting for fertilization. LH also stimulates oophore cumulus cells to release progesterone.
Ovulation: bursting of the follicle, oocyte leakage with pellucid zone, and radiated corona cells. The lining membrane is thinned on the ovary where the follicle bursts and the cells attached to it emerge from the stigma. The ovary is collected from the uterine tube, where fertilization can take place in the ampullate zone.
Formation of the corpus luteum: From the remaining structures of the follicle, the corpus luteum is formed. At first, there is a clot, which is then replaced by loose connective tissue; the cells that form solid cords are follicular cells and cells of the outer theca (Tecali lutein cells) and internal (granulosa cells). The luteal body increases the concentration of progesterone, which LH constantly stimulates. If the egg is not fertilized, the corpus luteum degenerates (body albicans); if it is implanted, it remains until three months of pregnancy, where its function is replaced by the placenta (production of progesterone and estrogen). The level of LH (necessary to keep the corpus luteum alive) is replaced by human chorionic gonadotropin. | Oogenesis | Wikipedia | 367 | 582473 | https://en.wikipedia.org/wiki/Oogenesis | Biology and health sciences | Animal reproduction | Biology |
Uterine cycle
The uterine cycle occurs parallel to the ovarian cycle and is induced by estrogen and progesterone. The endometrium, formed by a monostratified cylindrical epithelium, with uterine glands (simple tubular), connective with a functional superficial layer (divided into a spongy layer, a compact layer, and a deeper basal layer, which is always maintained, presents four phases:
Proliferative phase: From the 5th to the 14th day of the ovarian cycle, it is conditioned by estrogens. The functional layer of the uterus is restored, with mitotic division of the basal layer.
Secretive phase: from the 14th to the 27th day of the ovarian cycle, influenced by the progesterone produced by the corpus luteum. Cells become hypertrophic, and tubular glands begin to produce glycogen
Ischemic phase: beginning of the menstrual phase from 27 to 28 days
Regressive or desquamative phase from 1 to 5 days, the spiral-shaped arteries undergo ischemia, and the functional layer detaches
If, instead, there is fertilization, the uterine mucosa is modified to accommodate the fertilized egg, and the secretive phase is maintained.
Maturation into ovum
Both polar bodies disintegrate at the end of Meiosis II, leaving only the ootid, which then eventually undergoes maturation into a mature ovum.
The function of forming polar bodies is to discard the extra haploid sets of chromosomes that have resulted as a consequence of meiosis.
In vitro maturation
In vitro maturation (IVM) is the technique of letting ovarian follicles mature in vitro. It can potentially be performed before an IVF. In such cases, ovarian hyperstimulation is not essential. Rather, oocytes can mature outside the body prior to IVF. Hence, no (or at least a lower dose of) gonadotropins have to be injected in the body. Immature eggs have been grown until maturation in vitro at a 10% survival rate, but the technique is not yet clinically available. With this technique, cryopreserved ovarian tissue could possibly be used to make oocytes that can directly undergo in vitro fertilization. | Oogenesis | Wikipedia | 484 | 582473 | https://en.wikipedia.org/wiki/Oogenesis | Biology and health sciences | Animal reproduction | Biology |
In vitro oogenesis
By definition it means, to recapitulate mammalian oogenesis and producing fertilizable oocytes in vitro.it is a complex process involving several different cell types, precise follicular cell-oocyte reciprocal interactions, a variety of nutrients and combinations of cytokines, and precise growth factors and hormones depending on the developmental stage. In 2016, two papers published by Morohaku et al. and Hikabe et al. reported in vitro procedures that appear to reproduce efficiently these conditions allowing for the production, completely in a dish, of a relatively large number of oocytes that are fertilizable and capable of giving rise to viable offspring in the mouse. This technique can be mainly benefited in cancer patients where in today's condition their ovarian tissue
is cryopreserved for preservation of fertility. Alternatively to the autologous transplantation, the development of culture systems that support oocyte development from the primordial follicle stage represent a valid strategy to restore fertility. Over time, many studies have been conducted with the aim to optimize the characteristics of ovarian tissue culture systems and to better support the three main phases: 1) activation of primordial follicles; 2) isolation and culture of growing preantral follicles; 3) removal from the follicle environment and maturation of oocyte cumulus complexes. While complete oocyte in vitro development has been achieved in mouse, with the production of live offspring, the goal of obtaining oocytes of sufficient quality to support embryo development has not been completely reached into higher mammals despite decades of effort. | Oogenesis | Wikipedia | 338 | 582473 | https://en.wikipedia.org/wiki/Oogenesis | Biology and health sciences | Animal reproduction | Biology |
Ovarian aging
BRCA1 and ATM proteins are employed in repair of DNA double-strand break during meiosis. These proteins appear to have a critical role in resisting ovarian aging. However, homologous recombinational repair of DNA double-strand breaks mediated by BRCA1 and ATM weakens with age in oocytes of humans and other species. Women with BRCA1 mutations have lower ovarian reserves and experience earlier menopause than women without these mutations. Even in woman without specific BRCA1 mutations, ovarian aging is associated with depletion of ovarian reserves leading to menopause, but at a slower rate than in those with such mutations. Since older premenopausal women ordinarily have normal progeny, their capability for meiotic recombinational repair appears to be sufficient to prevent deterioration of their germline despite the reduction in ovarian reserve. DNA damages may arise in the germline during the decades long period in humans between early oocytogenesis and the stage of meiosis in which homologous chromosomes are effectively paired (dictyate stage). It has been suggested that such DNA damages may be removed, in large part, by mechanisms dependent on chromosome pairing, such as homologous recombination.
Oogenesis in non-mammals
Some algae and the oomycetes produce eggs in oogonia. In the brown alga Fucus, all four egg cells survive oogenesis, which is an exception to the rule that generally only one product of female meiosis survives to maturity.
In plants, oogenesis occurs inside the female gametophyte via mitosis. In many plants such as bryophytes, ferns, and gymnosperms, egg cells are formed in archegonia. In flowering plants, the female gametophyte has been reduced to an eight-celled embryo sac within the ovule inside the ovary of the flower. Oogenesis occurs within the embryo sac and leads to the formation of a single egg cell per ovule.
In ascaris, the oocyte does not even begin meiosis until the sperm touches it, in contrast to mammals, where meiosis is completed in the estrus cycle. | Oogenesis | Wikipedia | 468 | 582473 | https://en.wikipedia.org/wiki/Oogenesis | Biology and health sciences | Animal reproduction | Biology |
In female Drosophila flies, genetic recombination occurs during meiosis. This recombination is associated with formation of DNA double-strand breaks and the repair of these breaks.
The repair process leads to crossover recombinants as well as at least three times as many noncrossover recombinants (e.g. arising by gene conversion without crossover). | Oogenesis | Wikipedia | 78 | 582473 | https://en.wikipedia.org/wiki/Oogenesis | Biology and health sciences | Animal reproduction | Biology |
In thermodynamics, a quasi-static process, also known as a quasi-equilibrium process (from Latin quasi, meaning ‘as if’), is a thermodynamic process that happens slowly enough for the system to remain in internal physical (but not necessarily chemical) thermodynamic equilibrium. An example of this is quasi-static expansion of a mixture of hydrogen and oxygen gas, where the volume of the system changes so slowly that the pressure remains uniform throughout the system at each instant of time during the process. Such an idealized process is a succession of physical equilibrium states, characterized by infinite slowness.
Only in a quasi-static thermodynamic process can we exactly define intensive quantities (such as pressure, temperature, specific volume, specific entropy) of the system at any instant during the whole process; otherwise, since no internal equilibrium is established, different parts of the system would have different values of these quantities, so a single value per quantity may not be sufficient to represent the whole system. In other words, when an equation for a change in a state function contains P or T, it implies a quasi-static process.
Relation to reversible process
While all reversible processes are quasi-static, most authors do not require a general quasi-static process to maintain equilibrium between system and surroundings and avoid dissipation, which are defining characteristics of a reversible process. For example, quasi-static compression of a system by a piston subject to friction is irreversible; although the system is always in internal thermal equilibrium, the friction ensures the generation of dissipative entropy, which goes against the definition of reversibility. Any engineer would remember to include friction when calculating the dissipative entropy generation.
An example of a quasi-static process that is not idealizable as reversible is slow heat transfer between two bodies on two finitely different temperatures, where the heat transfer rate is controlled by a poorly conductive partition between the two bodies. In this case, no matter how slowly the process takes place, the state of the composite system consisting of the two bodies is far from equilibrium, since thermal equilibrium for this composite system requires that the two bodies be at the same temperature. Nevertheless, the entropy change for each body can be calculated using the Clausius equality for reversible heat transfer.
PV-work in various quasi-static processes | Quasistatic process | Wikipedia | 489 | 582702 | https://en.wikipedia.org/wiki/Quasistatic%20process | Physical sciences | Thermodynamics | Physics |
Constant pressure: Isobaric processes,
Constant volume: Isochoric processes,
Constant temperature: Isothermal processes, where (pressure) varies with (volume) via , so
Polytropic processes, | Quasistatic process | Wikipedia | 40 | 582702 | https://en.wikipedia.org/wiki/Quasistatic%20process | Physical sciences | Thermodynamics | Physics |
In thermodynamics, the particle number (symbol ) of a thermodynamic system is the number of constituent particles in that system. The particle number is a fundamental thermodynamic property which is conjugate to the chemical potential. Unlike most physical quantities, the particle number is a dimensionless quantity, specifically a countable quantity. It is an extensive property, as it is directly proportional to the size of the system under consideration and thus meaningful only for closed systems.
A constituent particle is one that cannot be broken into smaller pieces at the scale of energy involved in the process (where is the Boltzmann constant and is the temperature). For example, in a thermodynamic system consisting of a piston containing water vapour, the particle number is the number of water molecules in the system. The meaning of constituent particles, and thereby of particle numbers, is thus temperature-dependent.
Determining the particle number
The concept of particle number plays a major role in theoretical considerations. In situations where the actual particle number of a given thermodynamical system needs to be determined, mainly in chemistry, it is not practically possible to measure it directly by counting the particles. If the material is homogeneous and has a known amount of substance n expressed in moles, the particle number N can be found by the relation :
,
where NA is the Avogadro constant.
Particle number density
A related intensive system parameter is the particle number density （or particle number concentration PNC), a quantity of kind volumetric number density obtained by dividing the particle number of a system by its volume. This parameter is often denoted by the lower-case letter n.
In quantum mechanics
In quantum mechanical processes, the total number of particles may not be preserved. The concept is therefore generalized to the particle number operator, that is, the observable that counts the number of constituent particles. In quantum field theory, the particle number operator (see Fock state) is conjugate to the phase of the classical wave (see coherent state). | Particle number | Wikipedia | 414 | 582770 | https://en.wikipedia.org/wiki/Particle%20number | Physical sciences | Thermodynamics | Physics |
In air quality
One measure of air pollution used in air quality standards is the atmospheric concentration of particulate matter. This measure is usually expressed in μg/m3 (micrograms per cubic metre). In the current EU emission norms for cars, vans, and trucks and in the upcoming EU emission norm for non-road mobile machinery, particle number measurements and limits are defined, commonly referred to as PN, with units [#/km] or [#/kWh]. In this case, PN expresses a quantity of particles per unit distance (or work). | Particle number | Wikipedia | 117 | 582770 | https://en.wikipedia.org/wiki/Particle%20number | Physical sciences | Thermodynamics | Physics |
The standard atmosphere (symbol: atm) is a unit of pressure defined as Pa. It is sometimes used as a reference pressure or standard pressure. It is approximately equal to Earth's average atmospheric pressure at sea level.
History
The standard atmosphere was originally defined as the pressure exerted by a 760 mm column of mercury at and standard gravity (gn = ). It was used as a reference condition for physical and chemical properties, and the definition of the centigrade temperature scale set 100 °C as the boiling point of water at this pressure. In 1954, the 10th General Conference on Weights and Measures (CGPM) adopted standard atmosphere for general use and affirmed its definition of being precisely equal to dynes per square centimetre (). This defined pressure in a way that is independent of the properties of any particular substance. In addition, the CGPM noted that there had been some misapprehension that the previous definition (from the 9th CGPM) "led some physicists to believe that this definition of the standard atmosphere was valid only for accurate work in thermometry."
In chemistry and in various industries, the reference pressure referred to in standard temperature and pressure was commonly prior to 1982, but standards have since diverged; in 1982, the International Union of Pure and Applied Chemistry recommended that for the purposes of specifying the physical properties of substances, standard pressure should be precisely .
Pressure units and equivalencies
A pressure of 1 atm can also be stated as:
≈ kgf/cm2
≈ m H2O
≈ mmHg
≈ inHg
≈ in H2O
≈ pounds-force per square foot (lbf/ft2)
The notation ata has been used to indicate an absolute pressure measured in either standard atmospheres (atm) or technical atmospheres (at). | Standard atmosphere (unit) | Wikipedia | 368 | 582780 | https://en.wikipedia.org/wiki/Standard%20atmosphere%20%28unit%29 | Physical sciences | Energy, power, force and pressure | null |
The Video Graphics Array (VGA) connector is a standard connector used for computer video output. Originating with the 1987 IBM PS/2 and its VGA graphics system, the 15-pin connector went on to become ubiquitous on PCs, as well as many monitors, projectors and HD television sets.
Other connectors have been used to carry VGA-compatible signals, such as mini-VGA or BNC, but "VGA connector" typically refers to this design.
Devices continue to be manufactured with VGA connectors, although newer digital interfaces such as DVI, HDMI and DisplayPort are increasingly displacing VGA, and many modern computers and other devices do not include it.
Physical design
The VGA connector is a three-row, 15-pin D-subminiature connector referred to variously as DE-15, HD-15 or commonly DB-15(HD). DE-15 is the accurate nomenclature under the proprietary D-sub specifications: an "E" size D-sub connector, with 15 pins in three rows.
Predecessor and early variant
The standard 15-pin VGA connector was derived from the earlier DE-9 connector, which used the same "E" D-shell size (hence that connector's misnomer of DB-9 transferred its "DB" part to the new DE-15 connector as well, see above). Though IBM always used DE-15 connectors for their Video Graphics Array hardware, several VGA clone hardware makers initially did not. Instead, some early VGA hardware, both monitors and VGA cards, used a DE-9 connector for VGA, just like what had been in use for MDA, CGA, Hercules, and EGA. This 9-pin variant of the then-emerging de-facto standard 15-pin connector omitted several pins, which was considered acceptable, because the autodetection features supported by those pins only evolved over time, and prior to Windows 95, there was no user expectation of graphics cards and displays being fully plug and play. DE-9 VGA connectors were generally compatible with each other, and adaptors to the DE-15 standard were available. Ultimately all VGA hardware makers switched to standard DE-15 connectors, relegating the early variant to relative obscurity. | VGA connector | Wikipedia | 471 | 582844 | https://en.wikipedia.org/wiki/VGA%20connector | Technology | User interface | null |
Electrical design
All VGA connectors carry analog RGBHV (red, green, blue, horizontal sync, vertical sync) video signals. Modern connectors also include VESA DDC pins, for identifying attached display devices.
In both its modern and original variants, VGA utilizes multiple scan rates, so attached devices such as monitors are multisync by necessity.
The VGA interface includes no affordances for hot swapping, the ability to connect or disconnect the output device during operation, although in practice this can be done and usually does not cause damage to the hardware or other problems. The VESA DDC specification does, however, include a standard for hot-swapping.
PS/2 signaling
In the original IBM VGA implementation, refresh rates were limited to two vertical (60 and 70 Hz) frequencies, all of which were communicated to the monitor using combinations of different polarity H and V sync signals.
Some pins on the connector were also different: pin 9 was keyed by plugging the female connector hole, and four pins carried the monitor ID.
With the implementation of the VESA DDC specification, several of the monitor ID pins were reassigned for use by DDC signaling, and the key pin was replaced with a +5 V DC output per the DDC spec. Devices that comply with the DDC host system standard provide , from 50mA to 1A.
PS/55 signaling
The IBM PS/55 Display Adapter redefined pin 9 as "+12V", which signals the monitor to turn on when the system unit is powered on.
EDID
In order to advertise display capabilities VESA has introduced a scheme to redefining VGA connector pins 9, 12, and 15 as a serial bus for a Display Data Channel (DDC).
Cable quality
The same VGA cable can be used with a variety of supported VGA resolutions, ranging from 320×400px @70 Hz, or 320×480px @60 Hz (12.6 MHz of signal bandwidth) to 1280×1024px (SXGA) @85 Hz (160 MHz) and up to 2048×1536px (QXGA) @85 Hz (388 MHz).
There are no standards defining the quality required for each resolution, but higher-quality cables typically contain coaxial wiring and insulation that make them thicker. | VGA connector | Wikipedia | 486 | 582844 | https://en.wikipedia.org/wiki/VGA%20connector | Technology | User interface | null |
While shorter VGA cables are less likely to introduce significant signal degradation, good-quality cable should not suffer from signal crosstalk (whereby signals in one wire induce unwanted currents in adjacent wires) even at greater lengths.
Ghosting occurs when impedance mismatches cause signals to be reflected. A correctly impedance matched cable (75ohm) should prevent this, however, ghosting with long cables may be caused by equipment with incorrect signal termination or by passive cable splitters rather than the cables themselves.
Alternative connectors
Some high-end monitors and video cards used multiple BNC connectors instead of a single standard VGA connector, providing a higher quality connection with less crosstalk by utilising five separate 75 ohm coaxial cables. The use of BNC RGB video cables predates VGA in other markets and industries.
Within a 15-pin connector, the red, green, and blue signals (pins 1, 2, 3) cannot be shielded from each other, so crosstalk is possible within the 15-pin interconnect. BNC prevents crosstalk by maintaining full coaxial shielding through the circular connectors, but the connectors are very large and bulky. The requirement to press and turn the plug shell to disconnect requires access space around each connector to allow grasping of each BNC plug shell. Supplementary signals such as DDC are typically not supported with BNC.
Some laptops and other portable devices in the early to mid-2000s contained a two-row mini-VGA connector that is much smaller than the three-row DE-15 connector, as well as five separate BNC connectors.
Adapters
Various adapters can be purchased to convert VGA to other connector types. One common variety is a DVI to VGA adapter, which is possible because many DVI interfaces also carry VGA-compatible analog signals. Adapting from HDMI or DisplayPort to VGA without an active converter is not possible because those connectors don't output analog signals.
For conversions to and from digital formats like HDMI or Displayport, a scan converter is required. VGA outputs to interfaces with different signaling, more complex converters may be used. Most of them need an external power source to operate and are inherently lossy. However, many modern displays are still made with multiple inputs including VGA, in which case adapters are not necessary. | VGA connector | Wikipedia | 487 | 582844 | https://en.wikipedia.org/wiki/VGA%20connector | Technology | User interface | null |
VGA can also be adapted to SCART in some cases, because the signals are electrically compatible if the correct sync rates are set by the host PC. Many modern graphics adapters can modify their signal in software, including refresh rate, sync length, polarity and number of blank lines. Particular issues include interlace support and the use of the resolution 720×576 in PAL countries. Under these restrictive conditions, a simple circuit to combine the VGA separate synchronization signals into SCART composite sync may suffice.
Extenders
A VGA extender is an electronic device that increases the signal strength from a VGA port, most often from a computer. They are often used in schools, businesses, and homes when multiple monitors are being run off one VGA port, or if the cable between the monitor and the computer will be excessively long (often pictures appear blurry or have minor artifacts if the cable runs too far without an extender). VGA extenders are sometimes called VGA boosters. | VGA connector | Wikipedia | 208 | 582844 | https://en.wikipedia.org/wiki/VGA%20connector | Technology | User interface | null |
Oxygen cycle refers to the movement of oxygen through the atmosphere (air), biosphere (plants and animals) and the lithosphere (the Earth’s crust). The oxygen cycle demonstrates how free oxygen is made available in each of these regions, as well as how it is used. The oxygen cycle is the biogeochemical cycle of oxygen atoms between different oxidation states in ions, oxides, and molecules through redox reactions within and between the spheres/reservoirs of the planet Earth. The word oxygen in the literature typically refers to the most common oxygen allotrope, elemental/diatomic oxygen (O2), as it is a common product or reactant of many biogeochemical redox reactions within the cycle. Processes within the oxygen cycle are considered to be biological or geological and are evaluated as either a source (O2 production) or sink (O2 consumption).
Oxygen is one of the most common elements on Earth and represents a large portion of each main reservoir. By far the largest reservoir of Earth's oxygen is within the silicate and oxide minerals of the crust and mantle (99.5% by weight). The Earth's atmosphere, hydrosphere, and biosphere together hold less than 0.05% of the Earth's total mass of oxygen. Besides O2, additional oxygen atoms are present in various forms spread throughout the surface reservoirs in the molecules of biomass, H2O, CO2, HNO3, NO, NO2, CO, H2O2, O3, SO2, H2SO4, MgO, CaO, Al2O3, SiO2, and PO4.
Atmosphere
The atmosphere is 21% oxygen by volume, which equates to a total of roughly 34 × 1018 mol of oxygen. Other oxygen-containing molecules in the atmosphere include ozone (O3), carbon dioxide (CO2), water vapor (H2O), and sulphur and nitrogen oxides (SO2, NO, N2O, etc.).
Biosphere
The biosphere is 22% oxygen by volume, present mainly as a component of organic molecules (CxHxNxOx) and water.
Hydrosphere
The hydrosphere is 33% oxygen by volume present mainly as a component of water molecules, with dissolved molecules including free oxygen and carbolic acids (HxCO3). | Oxygen cycle | Wikipedia | 492 | 583598 | https://en.wikipedia.org/wiki/Oxygen%20cycle | Physical sciences | Earth science basics: General | Earth science |
Lithosphere
The lithosphere is 46.6% oxygen by volume, present mainly as silica minerals (SiO2) and other oxide minerals.
Sources and sinks
While there are many abiotic sources and sinks for O2, the presence of the profuse concentration of free oxygen in modern Earth's atmosphere and ocean is attributed to O2 production from the biological process of oxygenic photosynthesis in conjunction with a biological sink known as the biological pump and a geologic process of carbon burial involving plate tectonics. Biology is the main driver of O2 flux on modern Earth, and the evolution of oxygenic photosynthesis by bacteria, which is discussed as part of the Great Oxygenation Event, is thought to be directly responsible for the conditions permitting the development and existence of all complex eukaryotic metabolism.
Biological production
The main source of atmospheric free oxygen is photosynthesis, which produces sugars and free oxygen from carbon dioxide and water:
Photosynthesizing organisms include the plant life of the land areas, as well as the phytoplankton of the oceans. The tiny marine cyanobacterium Prochlorococcus was discovered in 1986 and accounts for up to half of the photosynthesis of the open oceans.
Abiotic production
An additional source of atmospheric free oxygen comes from photolysis, whereby high-energy ultraviolet radiation breaks down atmospheric water and nitrous oxide into component atoms. The free hydrogen and nitrogen atoms escape into space, leaving O2 in the atmosphere:
Biological consumption
The main way free oxygen is lost from the atmosphere is via respiration and decay, mechanisms in which animal life and bacteria consume oxygen and release carbon dioxide.
Capacities and fluxes
The following tables offer estimates of oxygen cycle reservoir capacities and fluxes.
These numbers are based primarily on estimates from (Walker, J. C. G.): More recent research indicates that ocean life (marine primary production) is actually responsible for more than half the total oxygen production on Earth.
Table 2: Annual gain and loss of atmospheric oxygen (Units of 1010 kg O2 per year)
Ozone
The presence of atmospheric oxygen has led to the formation of ozone (O3) and the ozone layer within the stratosphere:
O + O2 :- O3
The ozone layer is extremely important to modern life as it absorbs harmful ultraviolet radiation: | Oxygen cycle | Wikipedia | 478 | 583598 | https://en.wikipedia.org/wiki/Oxygen%20cycle | Physical sciences | Earth science basics: General | Earth science |
Amitriptyline, sold under the brand name Elavil among others, is a tricyclic antidepressant primarily used to treat major depressive disorder, and a variety of pain syndromes such as neuropathic pain, fibromyalgia, migraine and tension headaches. Due to the frequency and prominence of side effects, amitriptyline is generally considered a second-line therapy for these indications.
The most common side effects are dry mouth, drowsiness, dizziness, constipation, and weight gain. Glaucoma, liver toxicity and abnormal heart rhythms are rare but serious side effects. Blood levels of amitriptyline vary significantly from one person to another, and amitriptyline interacts with many other medications potentially aggravating its side effects.
Amitriptyline was discovered in the late 1950s by scientists at Merck and approved by the US Food and Drug Administration (FDA) in 1961. It is on the World Health Organization's List of Essential Medicines. It is available as a generic medication. In 2022, it was the 87th most commonly prescribed medication in the United States, with more than 7million prescriptions.
Medical uses
Amitriptyline is indicated for the treatment of major depressive disorder, neuropathic pain, and for the prevention of migraine and chronic tension headache. It can be used for the treatment of nocturnal enuresis in children older than 6 after other treatments have failed.
Depression
Amitriptyline is effective for depression, but it is rarely used as a first-line antidepressant due to its higher toxicity in overdose and generally poorer tolerability. It can be tried for depression as a second-line therapy, after the failure of other treatments. For treatment-resistant adolescent depression or for cancer-related depression amitriptyline is no better than placebo; however, the number of treated patients in both studies was small. It is sometimes used for the treatment of depression in Parkinson's disease, but supporting evidence for that is lacking. | Amitriptyline | Wikipedia | 418 | 583678 | https://en.wikipedia.org/wiki/Amitriptyline | Biology and health sciences | Psychiatric drugs | Health |
Pain
Amitriptyline alleviates painful diabetic neuropathy. It is recommended by a variety of guidelines as a first or second-line treatment. It is as effective for this indication as gabapentin or pregabalin but less well tolerated. Amitriptyline is as effective at relieving pain as duloxetine. Combination treatment of amitriptyline and pregabalin offers additional pain relief for people whose pain is not adequately controlled with one medication and is usually safe. Amitriptyline in certain formulations may also induce the level of sciatic-nerve blockade needed for local anesthesia therein. Here, it has been demonstrated to be of superior potency to bupivacaine, a customary long-acting local anesthetic.
Low doses of amitriptyline moderately improve sleep disturbances and reduce pain and fatigue associated with fibromyalgia. It is recommended for fibromyalgia accompanied by depression by Association of the Scientific Medical Societies in Germany and as a second-line option for fibromyalgia, with exercise being the first line option, by European League Against Rheumatism. Combinations of amitriptyline and fluoxetine or melatonin may reduce fibromyalgia pain better than either medication alone.
There is some (low-quality) evidence that amitriptyline may reduce pain in cancer patients. It is recommended only as a second-line therapy for non-chemotherapy-induced neuropathic or mixed neuropathic pain if opioids did not provide the desired effect.
Moderate evidence exists in favor of amitriptyline use for atypical facial pain. Amitriptyline is ineffective for HIV-associated neuropathy.
In multiple sclerosis, it is frequently used to treat painful paresthesias in the arms and legs (e.g., burning sensations, pins and needles, stabbing pains) caused by damage to the pain-regulating pathways of the brain and spinal cord.
Headache
Amitriptyline is probably effective for the prevention of periodic migraine in adults. Amitriptyline is similar in efficacy to venlafaxine and topiramate but carries a higher burden of adverse effects than topiramate. For many patients, even very small doses of amitriptyline are helpful, which may allow for minimization of side effects. Amitriptyline is not significantly different from placebo when used for the prevention of migraine in children. | Amitriptyline | Wikipedia | 505 | 583678 | https://en.wikipedia.org/wiki/Amitriptyline | Biology and health sciences | Psychiatric drugs | Health |
Amitriptyline may reduce the frequency and duration of chronic tension headache, but it is associated with worse adverse effects than mirtazapine. Overall, amitriptyline is recommended for tension headache prophylaxis, along with lifestyle advice, which should include avoidance of analgesia and caffeine.
Other indications
Amitriptyline is effective for the treatment of irritable bowel syndrome; however, because of its side effects, it should be reserved for select patients for whom other agents do not work. There is insufficient evidence to support its use for abdominal pain in children with functional gastrointestinal disorders.
Tricyclic antidepressants decrease the frequency, severity, and duration of cyclic vomiting syndrome episodes. Amitriptyline, as the most commonly used of them, is recommended as a first-line agent for its therapy.
Amitriptyline may improve pain and urgency intensity associated with bladder pain syndrome and can be used in the management of this syndrome. Amitriptyline can be used in the treatment of nocturnal enuresis in children. However, its effect is not sustained after the treatment ends. Alarm therapy gives better short- and long-term results.
In the US, amitriptyline is commonly used in children with ADHD as an adjunct to stimulant medications without any evidence or guideline supporting this practice. Many physicians in the UK (and the US also) commonly prescribe amitriptyline for insomnia; however, Cochrane reviewers were not able to find any randomized controlled studies that would support or refute this practice. Similarly, a major systematic review and network meta-analysis of medications for the treatment of insomnia published in 2022 found little evidence to inform the use of amitriptyline for insomnia. The well-known sedating effects of amitriptyline, however, bear understanding on and arguable justification for this practice. It may function similarly to doxepin in this regard, although the evidence for doxepin is more robust. Trimipramine may be a more novel alternative given its tendency to not suppress but brighten R.E.M. sleep.
Contraindications and precautions
The known contraindications of amitriptyline are: | Amitriptyline | Wikipedia | 461 | 583678 | https://en.wikipedia.org/wiki/Amitriptyline | Biology and health sciences | Psychiatric drugs | Health |
History of myocardial infarction
History of arrhythmias, particularly any degree of heart block
Coronary artery disease
Porphyria
Severe liver disease (such as cirrhosis)
Being under six years of age
Patients who are taking monoamine oxidase inhibitors (MAOIs) or have taken them within the last 14 days
Amitriptyline should be used with caution in patients with epilepsy, impaired liver function, pheochromocytoma, urinary retention, prostate enlargement, hyperthyroidism, and pyloric stenosis.
In patients with the rare condition of shallow anterior chamber of eyeball and narrow anterior chamber angle, amitriptyline may provoke attacks of acute glaucoma due to dilation of the pupil. It may aggravate psychosis, if used for depression with schizophrenia. It may precipitate the switch to mania in those with bipolar disorder.
CYP2D6 poor metabolizers should avoid amitriptyline due to increased side effects. If it is necessary to use it, half dose is recommended. Amitriptyline can be used during pregnancy and lactation when SSRIs have been shown not to work.
Side effects
The most frequent side effects, occurring in 20% or more of users, are dry mouth, drowsiness, dizziness, constipation, and weight gain (on average 1.8 kg). Other common side effects are headache problems (amblyopia, blurred vision), tachycardia, increased appetite, tremor, fatigue/asthenia/feeling slowed down, and dyspepsia.
A less common side effect of amitriptyline is urination problems (8.7%).
Amitriptyline can increase suicidal thoughts and behavior in people under the age of 24 and the US FDA required a boxed warning to be added to the prescription label. Amitriptyline-associated sexual dysfunction (occurring at a frequency of 6.9%) seems to be mostly confined to males with depression and is expressed predominantly as erectile dysfunction and low libido disorder, with lesser frequency of ejaculatory and orgasmic problems. The rate of sexual dysfunction in males treated for indications other than depression and in females is not significantly different from placebo. | Amitriptyline | Wikipedia | 469 | 583678 | https://en.wikipedia.org/wiki/Amitriptyline | Biology and health sciences | Psychiatric drugs | Health |
Liver test abnormalities occur in 10–12% of patients on amitriptyline, but are usually mild, asymptomatic, and transient, with consistently elevated alanine transaminase in 3% of all patients. The increases of the enzymes above the 3-fold threshold of liver toxicity are uncommon, and cases of clinically apparent liver toxicity are rare; nevertheless, amitriptyline is placed in the group of antidepressants with greater risks of hepatic toxicity.
Amitriptyline prolongs the QT interval. This prolongation is relatively small at therapeutic doses but becomes severe in overdose.
Overdose
The symptoms and the treatment of an overdose are largely the same as for the other TCAs, including the presentation of serotonin syndrome and adverse cardiac effects. The British National Formulary notes that amitriptyline can be particularly dangerous in overdose, thus it and other TCAs are no longer recommended as first-line therapy for depression. The treatment of overdose is mostly supportive as no specific antidote for amitriptyline overdose is available. Activated charcoal may reduce absorption if given within 1–2 hours of ingestion. If the affected person is unconscious or has an impaired gag reflex, a nasogastric tube may be used to deliver the activated charcoal into the stomach. ECG monitoring for cardiac conduction abnormalities is essential and if one is found close monitoring of cardiac function is advised. Body temperature should be regulated with measures such as heating blankets if necessary. Cardiac monitoring is advised for at least five days after the overdose. Benzodiazepines are recommended to control seizures. Dialysis is of no use due to the high degree of protein binding with amitriptyline.
Interactions | Amitriptyline | Wikipedia | 348 | 583678 | https://en.wikipedia.org/wiki/Amitriptyline | Biology and health sciences | Psychiatric drugs | Health |
Since amitriptyline and its active metabolite nortriptyline are primarily metabolized by cytochromes CYP2D6 and CYP2C19 (see its pharmacology), the inhibitors of these enzymes are expected to exhibit pharmacokinetic interactions with amitriptyline. According to the prescribing information, the interaction with CYP2D6 inhibitors may increase the plasma level of amitriptyline. However, the results in the other literature are inconsistent: the co-administration of amitriptyline with a potent CYP2D6 inhibitor paroxetine does increase the plasma levels of amitriptyline two-fold and of the main active metabolite nortriptyline 1.5-fold, but combination with less potent CYP2D6 inhibitors thioridazine or levomepromazine does not affect the levels of amitriptyline and increases nortriptyline by about 1.5-fold; A case of clinically significant interaction with potent CYP2D6 inhibitor terbinafine has been reported.
A potent inhibitor of CYP2C19 and other cytochromes fluvoxamine increases the level of amitriptyline two-fold while slightly decreasing the level of nortriptyline. Similar changes occur with a moderate inhibitor of CYP2C19 and other cytochromes cimetidine: amitriptyline level increases by about 70%, while nortriptyline decreases by 50%. CYP3A4 inhibitor ketoconazole elevates amitriptyline level by about a quarter. On the other hand, cytochrome P450 inducers such as carbamazepine and St. John's Wort decrease the levels of both amitriptyline and nortriptyline
Oral contraceptives may increase the blood level of amitriptyline by as high as 90%. Valproate moderately increases the levels of amitriptyline and nortriptyline through an unclear mechanism. | Amitriptyline | Wikipedia | 421 | 583678 | https://en.wikipedia.org/wiki/Amitriptyline | Biology and health sciences | Psychiatric drugs | Health |
The prescribing information warns that the combination of amitriptyline with monoamine oxidase inhibitors may cause potentially lethal serotonin syndrome; however, this has been disputed. The prescribing information cautions that some patients may experience a large increase in amitriptyline concentration in the presence of topiramate. However, other literature states that there is little or no interaction: in a pharmacokinetic study topiramate only increased the level of amitriptyline by 20% and nortriptyline by 33%.
Amitriptyline counteracts the antihypertensive action of guanethidine. When given with amitriptyline, other anticholinergic agents may result in hyperpyrexia or paralytic ileus. Co-administration of amitriptyline and disulfiram is not recommended due to the potential for the development of toxic delirium. Amitriptyline causes an unusual type of interaction with the anticoagulant phenprocoumon during which great fluctuations of the prothrombin time have been observed.
Pharmacology
Pharmacodynamics
Amitriptyline inhibits serotonin transporter (SERT) and norepinephrine transporter (NET). It is metabolized to nortriptyline, a stronger norepinephrine reuptake inhibitor, further augmenting amitriptyline's effects on norepinephrine reuptake (see table in this section).
Amitriptyline additionally acts as a potent inhibitor of the serotonin 5-HT2A, 5-HT2C, the α1A-adrenergic, the histamine H1 and the M1-M5 muscarinic acetylcholine receptors (see table in this section).
Amitriptyline is a non-selective blocker of multiple ion channels, in particular, voltage-gated sodium channels Nav1.3, Nav1.5, Nav1.6, Nav1.7, and Nav1.8, voltage-gated potassium channels Kv7.2/ Kv7.3, Kv7.1, Kv7.1/KCNE1, and hERG. | Amitriptyline | Wikipedia | 475 | 583678 | https://en.wikipedia.org/wiki/Amitriptyline | Biology and health sciences | Psychiatric drugs | Health |
Mechanism of action
Inhibition of serotonin and norepinephrine transporters by amitriptyline results in interference with neuronal reuptake of serotonin and norepinephrine. Since the reuptake process is important physiologically in terminating transmitting activity, this action may potentiate or prolong the activity of serotonergic and adrenergic neurons and is believed to underlie the antidepressant activity of amitriptyline.
Inhibition of norepinephrine reuptake leads to an increased concentration of norepinephrine in the posterior gray column of the spinal cord appears to be mostly responsible for the analgesic action of amitriptyline. Increased level of norepinephrine increases the basal activity of alpha-2 adrenergic receptors, which mediate an analgesic effect by increasing gamma-aminobutyric acid transmission among spinal interneurons. The blocking effect of amitriptyline on sodium channels may also contribute to its efficacy in pain conditions.
Pharmacokinetics
Amitriptyline is readily absorbed from the gastrointestinal tract (90–95%). Absorption is gradual with the peak concentration in blood plasma reached after about 4 hours. Extensive metabolism on the first pass through the liver leads to average bioavailability of about 50% (45%-53%). Amitriptyline is metabolized mostly by CYP2C19 into nortriptyline and by CYP2D6 leading to a variety of hydroxylated metabolites, with the principal one among them being (E)-10-hydroxynortriptyline (see metabolism scheme), and to a lesser degree, by CYP3A4.
Nortriptyline, the main active metabolite of amitriptyline, is an antidepressant on its own right. Nortriptyline reaches 10% higher level in the blood plasma than the parent drug amitriptyline and 40% greater area under the curve, and its action is an important part of the overall action of amitriptyline. | Amitriptyline | Wikipedia | 433 | 583678 | https://en.wikipedia.org/wiki/Amitriptyline | Biology and health sciences | Psychiatric drugs | Health |
Another active metabolite is (E)-10-hydroxynortriptyline, which is a norepinephrine uptake inhibitor four times weaker than nortriptyline. (E)-10-hydroxynortiptyline blood level is comparable to that of nortriptyline, but its cerebrospinal fluid level, which is a close proxy of the brain concentration of a drug, is twice higher than nortriptyline's. Based on this, (E)-10-hydroxynortriptyline was suggested to significantly contribute to the antidepressant effects of amitriptyline.
Blood levels of amitriptyline and nortriptyline and pharmacokinetics of amitriptyline in general, with clearance difference of up to 10-fold, vary widely between individuals. Variability of the area under the curve in steady state is also high, which makes a slow upward titration of the dose necessary.
In the blood, amitriptyline is 96% bound to plasma proteins; nortriptyline is 93–95% bound, and (E)-10-hydroxynortiptyline is about 60% bound. Amitriptyline has an elimination half life of 21 hours, nortriptyline – 23–31 hours, and (E)-10-hydroxynortiptyline − 8–10 hours. Within 48 hours, 12−80% of amitriptyline is eliminated in the urine, mostly as metabolites. 2% of the unchanged drug is excreted in the urine. Elimination in the feces, apparently, have not been studied.
Therapeutic levels of amitriptyline range from 75 to 175 ng/mL (270–631 nM), or 80–250 ng/mL of both amitriptyline and its metabolite nortriptyline.
Pharmacogenetics
Since amitriptyline is primarily metabolized by CYP2D6 and CYP2C19, genetic variations within the genes coding for these enzymes can affect its metabolism, leading to changes in the concentrations of the drug in the body. Increased concentrations of amitriptyline may increase the risk for side effects, including anticholinergic and nervous system adverse effects, while decreased concentrations may reduce the drug's efficacy. | Amitriptyline | Wikipedia | 479 | 583678 | https://en.wikipedia.org/wiki/Amitriptyline | Biology and health sciences | Psychiatric drugs | Health |
Individuals can be categorized into different types of CYP2D6 or CYP2C19 metabolizers depending on which genetic variations they carry. These metabolizer types include poor, intermediate, extensive, and ultrarapid metabolizers. Most individuals (about 77–92%) are extensive metabolizers, and have "normal" metabolism of amitriptyline. Poor and intermediate metabolizers have reduced metabolism of the drug as compared to extensive metabolizers; patients with these metabolizer types may have an increased probability of experiencing side effects. Ultrarapid metabolizers use amitriptyline much faster than extensive metabolizers; patients with this metabolizer type may have a greater chance of experiencing pharmacological failure.
The Clinical Pharmacogenetics Implementation Consortium recommends avoiding amitriptyline in patients who are CYP2D6 ultrarapid or poor metabolizers, due to the risk of a lack of efficacy and side effects, respectively. The consortium also recommends considering an alternative drug not metabolized by CYP2C19 in patients who are CYP2C19 ultrarapid metabolizers. A reduction in the starting dose is recommended for patients who are CYP2D6 intermediate metabolizers and CYP2C19 poor metabolizers. If the use of amitriptyline is warranted, therapeutic drug monitoring is recommended to guide dose adjustments. The Dutch Pharmacogenetics Working Group also recommends selecting an alternative drug or monitoring plasma concentrations of amitriptyline in patients who are CYP2D6 poor or ultrarapid metabolizers, and selecting an alternative drug or reducing initial dose in patients who are CYP2D6 intermediate metabolizers.
Chemistry
Amitriptyline is a highly lipophilic molecule having an octanol-water partition coefficient (pH 7.4) of 3.0, while the log P of the free base was reported as 4.92. Solubility of the free base amitriptyline in water is 14 mg/L. Amitriptyline is prepared by reacting dibenzosuberane with 3-(dimethylamino)propylmagnesium chloride and then heating the resulting intermediate product with hydrochloric acid to eliminate water. | Amitriptyline | Wikipedia | 482 | 583678 | https://en.wikipedia.org/wiki/Amitriptyline | Biology and health sciences | Psychiatric drugs | Health |
History
Amitriptyline was first developed by the American pharmaceutical company Merck in the late 1950s. In 1958, Merck approached several clinical investigators proposing to conduct clinical trials of amitriptyline for schizophrenia. One of these researchers, Frank Ayd, instead, suggested using amitriptyline for depression. Ayd treated 130 patients and, in 1960, reported that amitriptyline had antidepressant properties similar to another, and the only known at the time, tricyclic antidepressant imipramine. Following this, the US Food and Drug Administration approved amitriptyline for depression in 1961.
In Europe, due to a quirk of the patent law at the time allowing patents only on the chemical synthesis but not on the drug itself, Roche and Lundbeck were able to independently develop and market amitriptyline in the early 1960s.
According to research by a historian of psychopharmacology David Healy, amitriptyline became a much bigger selling drug than its precursor imipramine because of two factors. First, amitriptyline has a much stronger anxiolytic effect. Second, Merck conducted a marketing campaign raising clinicians' awareness of depression as a clinical entity.
Society and culture
In the 2021 film The Many Saints of Newark, amitriptyline (referred to by the brand name Elavil) is part of the plot line of the movie.
Names
Amitriptyline is the English and French generic name of the drug and its , , and , while amitriptyline hydrochloride is its , , , and . Its generic name in Spanish and Italian and its are , in German is , and in Latin is . The embonate salt is known as amitriptyline embonate, which is its BANM, or as amitriptyline pamoate unofficially.
Prescription trends
Between 1998 and 2017, along with imipramine, amitriptyline was the most commonly prescribed first antidepressant for children aged 5–11 years in England. It was also the most prescribed antidepressant (along with fluoxetine) for 12- to 17-year-olds.
Research
The few randomized controlled trials investigating amitriptyline efficacy in eating disorder have been discouraging. | Amitriptyline | Wikipedia | 465 | 583678 | https://en.wikipedia.org/wiki/Amitriptyline | Biology and health sciences | Psychiatric drugs | Health |
A safety razor is a shaving implement with a protective device positioned between the edge of the blade and the skin. The initial purpose of these protective devices was to reduce the level of skill needed for injury-free shaving, thereby reducing the reliance on professional barbers.
Protective devices for razors have existed since at least the 1700s: a circa 1762 invention by French cutler Jean-Jacques Perret added a protective guard to a regular straight razor. The first known occurrence of the term "safety razor" is found in a patent from 1880 for a razor in the basic contemporary configuration with a handle in which a removable blade is placed (although this form predated the patent).
Safety razors were popularized in the 1900s by King Camp Gillette's invention, the double-edge safety razor. While other safety razors of the time used blades that required stropping before use and after a time had to be honed by a cutler, Gillette's razor used a disposable blade with two sharpened edges. Gillette's invention became the predominant style of razor during and after the First World War, when the U.S. Army began issuing Gillette shaving kits to its servicemen.
Since their introduction in the 1970s, cartridge razors and disposable razors – where the blades are embedded in plastic – have become the predominant types of safety razors. In 2010, Procter & Gamble stated that almost a billion men were shaving with double-edge razors.
History
Early designs
The first step towards a safer-to-use razor was the guard razor – also called a straight safety razor – which added a protective guard to a regular straight razor. The first such razor was most likely invented by French cutler Jean-Jacques Perret circa 1762. The invention was inspired by the joiner's plane and was essentially a straight razor with its blade surrounded by a wooden sleeve. The earliest razor guards had comb-like teeth and could only be attached to one side of a razor; a reversible guard was one of the first improvements made to guard razors.
The basic form of a razor, "the cutting blade of which is at right angles with the handle, and resembles somewhat the form of a common hoe", was first described in a patent application in 1847 by William S. Henson. This also covered a "comb tooth guard or protector" which could be attached both to the hoe form and to a conventional straight razor. | Safety razor | Wikipedia | 501 | 583832 | https://en.wikipedia.org/wiki/Safety%20razor | Biology and health sciences | Hygiene products | Health |
The first attested use of the term "safety razor" is in a patent application for "new and useful improvements in Safety-Razors", filed in May 1880 by Frederic and Otto Kampfe of Brooklyn, New York, and issued the following month. This differed from the Henson design in distancing the blade from the handle by interposing "a hollow metallic blade-holder having a preferably removable handle and a flat plate in front, to which the blade is attached by clips and a pivoted catch, said plate having bars or teeth at its lower edge, and the lower plate having an opening, for the purpose set forth", which is to "insure a smooth bearing for the plate upon the skin, while the teeth or bars will yield sufficiently to allow the razor to sever the hair without danger of cutting the skin." The Kampfe Brothers produced razors under their own name following the 1880 patent and improved the design in a series of subsequent patents. These models were manufactured under the "Star Safety Razor" brand.
A third pivotal innovation was a safety razor using a disposable double-edge blade for which King Camp Gillette submitted a patent application in 1901 and was granted in 1904. The Gillette Safety Razor Company was awarded a contract to supply the American troops in World War I with double-edge safety razors as part of their standard field kits (delivering a total of 3.5 million razors and 32 million blades for them). The returning soldiers were permitted to keep that part of their equipment and therefore retained their new shaving habits. The subsequent consumer demand for replacement blades put the shaving industry on course toward its present form with Gillette as a dominant force. Prior to the introduction of the disposable blade, users of safety razors still needed to strop and hone the edges of their blades. These are not trivial skills (honing frequently being left to a professional) and remained a barrier to the ubiquitous adopting of the "be your own barber" ideal.
Single-edge razors | Safety razor | Wikipedia | 418 | 583832 | https://en.wikipedia.org/wiki/Safety%20razor | Biology and health sciences | Hygiene products | Health |
The first safety razors used a single-edge blade that was essentially a long segment of a straight razor. A flat blade that could be used alternately with this "wedge" was first illustrated in a patent issued in 1878, serving as a close prototype for the single-edge blade in its present form. New single-edge razors were developed and used side by side with double-edge razors for decades. The largest manufacturers were the American Safety Razor Company with its "Ever-Ready" series, and the Gem Cutlery Company with its "Gem" models. Although these brands of single-edge razors are no longer in production, they are readily available in antique trade, and compatible modern designs are being made. Blades for them are still being manufactured both for shaving and technical purposes.
A second popular single-edge design is the "Injector" razor developed and placed on the market by Schick Razors in the 1920s. This uses narrow blades stored in an injector device with which they are inserted directly into the razor, so that the user never needs to handle the blade. The injector blade was the first to depart from the rectangular dimensions shared by the wedge, standard single-edge, and double-edge blades. The injector, itself, was also the first device intended to reduce the risk of injury from handling blades. The Gillette blade dispenser released in 1947 had the same purpose. The narrow injector blade, as well as the form of the injector razor, also strongly influenced the corresponding details of the subsequently developed cartridge razors. Both injector blades and injector safety razors are still available on the market, from antique stock as well as modern manufacture. The injector blades have also inspired a variety of specialised blades for professional barber use, some of which have been re-adopted for shaving by modern designs. | Safety razor | Wikipedia | 386 | 583832 | https://en.wikipedia.org/wiki/Safety%20razor | Biology and health sciences | Hygiene products | Health |
Until the 1960s, razor blades were made of carbon steel. These were extremely prone to rusting and forced users to change blades frequently. In 1962, the British company Wilkinson Sword began to sell blades made of stainless steel, whose edge did not corrode nearly so quickly and could be used far longer. Wilkinson quickly captured U.S., British and European markets. As a result, American Safety Razor, Gillette and Schick were driven to produce stainless steel blades to compete. Today, almost all razor blades are stainless steel, although carbon steel blades remain in limited production for lower income markets. Because Gillette held a patent on stainless blades but had not acted on it, the company was accused of exploiting customers by forcing them to buy the rust-prone blade.
The risk of injury from handling razor blades was further reduced in 1970 when Wilkinson released its "Bonded Shaving System", which embedded a single blade in a disposable polymer plastic cartridge. A flurry of competing models soon followed with everything from one to six blades, with many cartridge blade razors also having disposable handles. Cartridge blade razors are sometimes considered to be a generic category of their own and not a variety of safety razor. The similarities between single-edge cartridge blade razors and the classic injector razor do, however, provide equal justification for treating both categories contiguously.
In 1974, Bic introduced the disposable razor. Instead of being a razor with a disposable blade, the entire razor was manufactured to be disposable. Gillette's response was the Good News disposable razor which was launched on the US market in 1976 before the Bic disposable was made available on that market. Shortly thereafter, Gillette modified the Good News construction to add an aloe strip above the razor, resulting in the Good News Plus. The purported benefit of the aloe strip is to ease any discomfort felt on the face while shaving. | Safety razor | Wikipedia | 403 | 583832 | https://en.wikipedia.org/wiki/Safety%20razor | Biology and health sciences | Hygiene products | Health |
In direct response to Wilkinson's Bonded cartridge, during the following year Gillette introduced the twin-blade Trac II. They claimed that research showed the tandem action of the two blades to give a closer shave than a single blade, because of a "hysteresis" effect. In addition to the cutting action of the first blade, it is also supposed to pull the hair out of the follicle into which it does not fully retract before the second blade cuts it further. The extent to which this is of practical consequence has, however, been questioned.
Recent changes
Gillette introduced the first triple-blade cartridge razor, the Mach3, in 1998, and later upgraded the Sensor cartridge to the Sensor3 by adding a third blade. Schick/Wilkinson responded to the Mach3 with the Quattro, the first four-blade cartridge razor. These innovations are marketed with the message that they help consumers achieve the best shave as easily as possible. Another impetus for the sale of multiple-blade cartridges is that they have high profit margins. With manufacturers frequently updating their shaving systems, consumers can become locked into buying their proprietary cartridges, for as long as the manufacturer continues to make them. Subsequent to introducing the higher-priced Mach3 in 1998, Gillette's blade sales realized a 50% increase, and profits increased in an otherwise mature market. | Safety razor | Wikipedia | 278 | 583832 | https://en.wikipedia.org/wiki/Safety%20razor | Biology and health sciences | Hygiene products | Health |
The marketing of increasing numbers of blades in a cartridge has been parodied since the 1970s. The debut episode of Saturday Night Live in 1975 included a parody advertisement for the Triple Trac Razor, shortly after the first two-blade cartridge for men's razors was advertised. Mad magazine announced the "Trac 76", arranged as a chain of cartridges with a handle on each end. In the early 1990s, the (Australian) Late Show skitted a "Gillette 3000" with 16 blades and 75 lubricating strips as arrived at by working in conjunction with the help of NASA scientists - "The first blade distracts the hair...". The 16 January 1999 episode of Mad TV ran a parody commercial advertising the "Spishak Mach 20" with blades that variously "cut(s) away that pesky second layer of skin" and "gently smooth(s) out the jawbone" culminating in a blade that "destroys the part of the brain responsible for hair growth." In 2004, a satirical article in The Onion entitled "Fuck Everything, We're Doing Five Blades" predicted the release of five-blade cartridges, two years before their commercial introduction. South Korean manufacturer Dorco released their own six-blade cartridge in 2012, and later released a seven-blade cartridge.
Gillette has also produced powered variants of the Mach3 (M3Power, M3Power Nitro) and Fusion (Fusion Power and Fusion Power Phantom) razors. These razors accept a single AAA battery which is used to produce vibration in the razor; this action was purported to raise hair up and away from the skin prior to being cut. These claims were ruled in an American court as "unsubstantiated and inaccurate".
Design
Safety razors originally had an edge protected by a comb patterned on various types of protective guards that had been affixed to open-blade straight razors during the preceding decades.
Lifespan
To maintain their cutting action, razor blades can be stropped using an old strip of denim. Twinplex also sold a blade stropper which was used to extend the life of vintage carbon steel blades.
Safety razor blades are usually made of razor steel which is a low chromium stainless steel which can be made extremely sharp, but corrodes relatively easily. Safety razor blade life may be extended by drying the blades after use. Salts from human skin also tend to corrode the blades, but washing and carefully drying them can greatly extend their life. | Safety razor | Wikipedia | 503 | 583832 | https://en.wikipedia.org/wiki/Safety%20razor | Biology and health sciences | Hygiene products | Health |
Disposable safety razor blades can be sharpened using various methods. There are commercial devices intended for this duty (Razormate, RazorPit, Blade Buddy, etc.).
Variants
Double-edged razors
Double-edge (DE) safety razors remain a popular alternative to proprietary cartridge razors, and usually offer significantly lower total cost of ownership since they are not marketed under the "razor and blades business model". Double-edge razors are still designed and produced in many countries, and in 2010, Procter & Gamble estimated that almost a billion men were shaving with double-edge razors. Better known manufacturers include Edwin Jagger, Feather, iKon, Lord, Mühle, Merkur, and Weishi, with several of them producing razors that are marketed under other brands. Often different models of razors within a brand share the same razor-head designs, differing primarily in the color, length, texture, material(s), and weight of the handles. Three-piece razors generally have interchangeable handles, and some companies specialize in manufacturing custom or high-end replacement handles. The butterfly safety razor utilizes a twist-to-open mechanism head to make changing the blade easy and convenient. Variations in razor head designs include straight safety bar (SB), open comb (OC)(toothed) bar, adjustable razors, and slant bar razors. The slant bar was a common design in Germany in which the blade is slightly angled and curved along its length to make for a slicing action and a more rigid cutting edge.
A primary functional difference between double-edge razors and modern cartridge razors is that DE razor heads come in a wide array of aggression levels (where aggression is commonly defined as being less protection from the blade). | Safety razor | Wikipedia | 360 | 583832 | https://en.wikipedia.org/wiki/Safety%20razor | Biology and health sciences | Hygiene products | Health |
A combined cycle power plant is an assembly of heat engines that work in tandem from the same source of heat, converting it into mechanical energy. On land, when used to make electricity the most common type is called a combined cycle gas turbine (CCGT) plant, which is a kind of gas-fired power plant. The same principle is also used for marine propulsion, where it is called a combined gas and steam (COGAS) plant. Combining two or more thermodynamic cycles improves overall efficiency, which reduces fuel costs.
The principle is that after completing its cycle in the first engine, the working fluid (the exhaust) is still hot enough that a second subsequent heat engine can extract energy from the heat in the exhaust. Usually the heat passes through a heat exchanger so that the two engines can use different working fluids.
By generating power from multiple streams of work, the overall efficiency can be increased by 50–60%. That is, from an overall efficiency of the system of say 34% for a simple cycle, to as much as 64% net for the turbine alone in specified conditions for a combined cycle.
Historical cycles
Historically successful combined cycles have used mercury vapour turbines, magnetohydrodynamic generators and molten carbonate fuel cells, with steam plants for the low temperature "bottoming" cycle. Very low temperature bottoming cycles have been too costly due to the very large sizes of equipment needed to handle the large mass flows and small temperature differences. However, in cold climates it is common to sell hot power plant water for hot water and space heating. Vacuum-insulated piping can let this utility reach as far as 90 km. The approach is called "combined heat and power" (CHP).
In stationary and marine power plants, a widely used combined cycle has a large gas turbine (operating by the Brayton cycle). The turbine's hot exhaust powers a steam power plant (operating by the Rankine cycle). This is a combined cycle gas turbine (CCGT) plant. These achieve a best-of-class real (see below) thermal efficiency of around 64% in base-load operation. In contrast, a single cycle steam power plant is limited to efficiencies from 35 to 42%. Many new power plants utilize CCGTs. Stationary CCGTs burn natural gas or synthesis gas from coal. Ships burn fuel oil. | Combined cycle power plant | Wikipedia | 482 | 583901 | https://en.wikipedia.org/wiki/Combined%20cycle%20power%20plant | Technology | Power generation | null |
Multiple stage turbine or steam cycles can also be used, but CCGT plants have advantages for both electricity generation and marine power. The gas turbine cycle can often start very quickly, which gives immediate power. This avoids the need for separate expensive peaker plants, or lets a ship maneuver. Over time the secondary steam cycle will warm up, improving fuel efficiency and providing further power.
In November 2013, the Fraunhofer Institute for Solar Energy Systems ISE assessed the levelised cost of energy for newly built power plants in the German electricity sector. They gave costs of between 78 and €100 /MWh for CCGT plants powered by natural gas. In addition the capital costs of combined cycle power is relatively low, at around $1000/kW, making it one of the cheapest types of generation to install.
Basic combined cycle
The thermodynamic cycle of the basic combined cycle consists of two power plant cycles. One is the Joule or Brayton cycle which is a gas turbine cycle and the other is the Rankine cycle which is a steam turbine cycle. The cycle 1-2-3-4-1 which is the gas turbine power plant cycle is the topping cycle. It depicts the heat and work transfer process taking place in the high temperature region.
The cycle a-b-c-d-e-f-a which is the Rankine steam cycle takes place at a lower temperature and is known as the bottoming cycle. Transfer of heat energy from high temperature exhaust gas to water and steam takes place in a waste heat recovery boiler in the bottoming cycle. During the constant pressure process 4-1 the exhaust gases from the gas turbine reject heat. The feed water, wet and super heated steam absorb some of this heat in the process a-b, b-c and c-d.
Steam generators
The steam power plant takes its input heat from the high temperature exhaust gases from a gas turbine power plant. The steam thus generated can be used to drive a steam turbine. The Waste Heat Recovery Boiler (WHRB) has 3 sections: Economiser, evaporator and superheater.
Cheng cycle | Combined cycle power plant | Wikipedia | 430 | 583901 | https://en.wikipedia.org/wiki/Combined%20cycle%20power%20plant | Technology | Power generation | null |
The Cheng cycle is a simplified form of combined cycle where the steam turbine is eliminated by injecting steam directly into the combustion turbine. This has been used since the mid 1970s and allows recovery of waste heat with less total complexity, but at the loss of the additional power and redundancy of a true combined cycle system. It has no additional steam turbine or generator, and therefore it cannot be used as a backup or supplementary power. It is named after American professor D. Y. Cheng who patented the design in 1976.
Design principles
The efficiency of a heat engine, the fraction of input heat energy that can be converted to useful work, is limited by the temperature difference between the heat entering the engine and the exhaust heat leaving the engine.
In a thermal power station, water is the working medium. High pressure steam requires strong, bulky components. High temperatures require expensive alloys made from nickel or cobalt, rather than inexpensive steel. These alloys limit practical steam temperatures to 655 °C while the lower temperature of a steam plant is fixed by the temperature of the cooling water. With these limits, a steam plant has a fixed upper efficiency of 35–42%.
An open circuit gas turbine cycle has a compressor, a combustor and a turbine. For gas turbines the amount of metal that must withstand the high temperatures and pressures is small, and lower quantities of expensive materials can be used. In this type of cycle, the input temperature to the turbine (the firing temperature), is relatively high (900 to 1,400 °C). The output temperature of the flue gas is also high (450 to 650 °C). This is therefore high enough to provide heat for a second cycle which uses steam as the working fluid (a Rankine cycle).
In a combined cycle power plant, the heat of the gas turbine's exhaust is used to generate steam by passing it through a heat recovery steam generator (HRSG) with a live steam temperature between 420 and 580 °C. The condenser of the Rankine cycle is usually cooled by water from a lake, river, sea or cooling towers. This temperature can be as low as 15 °C.
Typical size
Plant size is important in the cost of the plant. The larger plant sizes benefit from economies of scale (lower initial cost per kilowatt) and improved efficiency. | Combined cycle power plant | Wikipedia | 466 | 583901 | https://en.wikipedia.org/wiki/Combined%20cycle%20power%20plant | Technology | Power generation | null |
For large-scale power generation, a typical set would be a 270 MW primary gas turbine coupled to a 130 MW secondary steam turbine, giving a total output of 400 MW. A typical power station might consist of between 1 and 6 such sets.
Gas turbines for large-scale power generation are manufactured by at least four separate groups – General Electric, Siemens, Mitsubishi-Hitachi, and Ansaldo Energia. These groups are also developing, testing and/or marketing gas turbine sizes in excess of 300 MW (for 60 Hz applications) and 400 MW (for 50 Hz applications). Combined cycle units are made up of one or more such gas turbines, each with a waste heat steam generator arranged to supply steam to a single or multiple steam turbines, thus forming a combined cycle block or unit. Combined cycle block sizes offered by three major manufacturers (Alstom, General Electric and Siemens) can range anywhere from 50 MW to well over 1300 MW with costs approaching $670/kW.
Unfired boiler
The heat recovery boiler is item 5 in the COGAS figure shown above. Hot gas turbine exhaust enters the super heater, then passes through the evaporator and finally through the economiser section as it flows out from the boiler. Feed water comes in through the economizer and then exits after having attained saturation temperature in the water or steam circuit. Finally it flows through the evaporator and super heater. If the temperature of the gases entering the heat recovery boiler is higher, then the temperature of the exiting gases is also high.
Dual pressure boiler
In order to remove the maximum amount of heat from the gasses exiting the high temperature cycle, a dual pressure boiler is often employed. It has two water/steam drums. The low-pressure drum is connected to the low-pressure economizer or evaporator. The low-pressure steam is generated in the low temperature zone of the turbine exhaust gasses. The low-pressure steam is supplied to the low-temperature turbine. A super heater can be provided in the low-pressure circuit.
Some part of the feed water from the low-pressure zone is transferred to the high-pressure economizer by a booster pump. This economizer heats up the water to its saturation temperature. This saturated water goes through the high-temperature zone of the boiler and is supplied to the high-pressure turbine. | Combined cycle power plant | Wikipedia | 487 | 583901 | https://en.wikipedia.org/wiki/Combined%20cycle%20power%20plant | Technology | Power generation | null |
Supplementary firing
The HRSG can be designed to burn supplementary fuel after the gas turbine. Supplementary burners are also called duct burners. Duct burning is possible because the turbine exhaust gas (flue gas) still contains some oxygen. Temperature limits at the gas turbine inlet force the turbine to use excess air, above the optimal stoichiometric ratio to burn the fuel. Often in gas turbine designs part of the compressed air flow bypasses the burner in order to cool the turbine blades. The turbine exhaust is already hot, so a regenerative air preheater is not required as in a conventional steam plant. However, a fresh air fan blowing directly into the duct permits a duct-burning steam plant to operate even when the gas turbine cannot.
Without supplementary firing, the thermal efficiency of a combined cycle power plant is higher. But more flexible plant operations make a marine CCGT safer by permitting a ship to operate with equipment failures. A flexible stationary plant can make more money. Duct burning raises the flue temperature, which increases the quantity or temperature of the steam (e.g. to 84 bar, 525 degree Celsius). This improves the efficiency of the steam cycle. Supplementary firing lets the plant respond to fluctuations of electrical load, because duct burners can have very good efficiency with partial loads. It can enable higher steam production to compensate for the failure of another unit. Also, coal can be burned in the steam generator as an economical supplementary fuel.
Supplementary firing can raise exhaust temperatures from 600 °C (GT exhaust) to 800 or even 1000 °C. Supplemental firing does not raise the efficiency of most combined cycles. For single boilers it can raise the efficiency if fired to 700–750 °C; for multiple boilers however, the flexibility of the plant should be the major attraction.
"Maximum supplementary firing" is the condition when the maximum fuel is fired with the oxygen available in the gas turbine exhaust.
Combined cycle advanced Rankine subatmospheric reheating
Fuel for combined cycle power plants | Combined cycle power plant | Wikipedia | 401 | 583901 | https://en.wikipedia.org/wiki/Combined%20cycle%20power%20plant | Technology | Power generation | null |
Combined cycle plants are usually powered by natural gas, although fuel oil, synthesis gas or other fuels can be used. The supplementary fuel may be natural gas, fuel oil, or coal. Biofuels can also be used. Integrated solar combined cycle power stations combine the energy harvested from solar radiation with another fuel to cut fuel costs and environmental impact (See: ISCC section). Many next generation nuclear power plants can use the higher temperature range of a Brayton top cycle, as well as the increase in thermal efficiency offered by a Rankine bottoming cycle.
Where the extension of a gas pipeline is impractical or cannot be economically justified, electricity needs in remote areas can be met with small-scale combined cycle plants using renewable fuels. Instead of natural gas, these gasify and burn agricultural and forestry waste, which is often readily available in rural areas.
Managing low-grade fuels in turbines
Gas turbines burn mainly natural gas and light oil. Crude oil, residual, and some distillates contain corrosive components and as such require fuel treatment equipment. In addition, ash deposits from these fuels result in gas turbine deratings of up to 15%. They may still be economically attractive fuels however, particularly in combined-cycle plants.
Sodium and potassium are removed from residual, crude and heavy distillates by a water washing procedure. A simpler and less expensive purification system will do the same job for light crude and light distillates. A magnesium additive system may also be needed to reduce the corrosive effects if vanadium is present. Fuels requiring such treatment must have a separate fuel-treatment plant and a system of accurate fuel monitoring to assure reliable, low-maintenance operation of gas turbines.
Hydrogen
Xcel Energy is going to build two natural gas power plants in the Midwestern United States that can mix 30% hydrogen with the natural gas. Intermountain Power Plant is being retrofitted to a natural gas/hydrogen power plant that can run on 30% hydrogen as well, and is scheduled to run on pure hydrogen by 2045. However others think low-carbon hydrogen should be used for things which are harder to decarbonize, such as making fertilizer, so there may not be enough for electricity generation.
Configuration
Combined-cycle systems can have single-shaft or multi-shaft configurations. Also, there are several configurations of steam systems. | Combined cycle power plant | Wikipedia | 480 | 583901 | https://en.wikipedia.org/wiki/Combined%20cycle%20power%20plant | Technology | Power generation | null |
The most fuel-efficient power generation cycles use an unfired heat recovery steam generator (HRSG) with modular pre-engineered components. These unfired steam cycles are also the lowest in initial cost, and they are often part of a single shaft system that is installed as a unit.
Supplementary-fired and multishaft combined-cycle systems are usually selected for specific fuels, applications or situations. For example, cogeneration combined-cycle systems sometimes need more heat, or higher temperatures, and electricity is a lower priority. Multishaft systems with supplementary firing can provide a wider range of temperatures or heat to electric power. Systems burning low quality fuels such as brown coal or peat might use relatively expensive closed-cycle helium turbines as the topping cycle to avoid even more expensive fuel processing and gasification that would be needed by a conventional gas turbine.
A typical single-shaft system has one gas turbine, one steam turbine, one generator and one heat recovery steam generator (HRSG). The gas turbine and steam turbine are both coupled in tandem to a single electrical generator on a single shaft. This arrangement is simpler to operate, smaller, with a lower startup cost.
Single-shaft arrangements can have less flexibility and reliability than multi-shaft systems. With some expense, there are ways to add operational flexibility: Most often, the operator desires to operate the gas turbine as a peaking plant. In these plants, the steam turbine's shaft can be disconnected with a synchro-self-shifting (SSS) clutch, for start up or for simple cycle operation of the gas turbine. Another less common set of options enable more heat or standalone operation of the steam turbine to increase reliability: Duct burning, perhaps with a fresh air blower in the duct and a clutch on the gas turbine side of the shaft.
A multi-shaft system usually has only one steam system for up to three gas turbines. Having only one large steam turbine and heat sink has economies of scale and can have lower cost operations and maintenance. A larger steam turbine can also use higher pressures, for a more efficient steam cycle. However, a multi-shaft system is about 5% higher in initial cost.
The overall plant size and the associated number of gas turbines required can also determine which type of plant is more economical. A collection of single shaft combined cycle power plants can be more costly to operate and maintain, because there are more pieces of equipment. However, it can save interest costs by letting a business add plant capacity as it is needed. | Combined cycle power plant | Wikipedia | 504 | 583901 | https://en.wikipedia.org/wiki/Combined%20cycle%20power%20plant | Technology | Power generation | null |
Multiple-pressure reheat steam cycles are applied to combined-cycle systems with gas turbines with exhaust gas temperatures near 600 °C. Single- and multiple-pressure non-reheat steam cycles are applied to combined-cycle systems with gas turbines that have exhaust gas temperatures of 540 °C or less. Selection of the steam cycle for a specific application is determined by an economic evaluation that considers a plant's installed cost, fuel cost and quality, duty cycle, and the costs of interest, business risks, and operations and maintenance.
Efficiency
By combining both gas and steam cycles, high input temperatures and low output temperatures can be achieved.
The efficiency of the cycles add, because they are powered by the same fuel source.
So, a combined cycle plant has a thermodynamic cycle that operates between the gas-turbine's high firing temperature and the waste heat temperature from the condensers of the steam cycle.
This large range means that the Carnot efficiency of the cycle is high.
The actual efficiency, while lower than the Carnot efficiency, is still higher than that of either plant on its own.
The electric efficiency of a combined cycle power station, if calculated as electric energy produced as a percentage of the lower heating value of the fuel consumed, can be over 60% when operating new, i.e. unaged, and at continuous output which are ideal conditions.
As with single cycle thermal units, combined cycle units may also deliver low temperature heat energy for industrial processes, district heating and other uses. This is called cogeneration and such power plants are often referred to as a combined heat and power (CHP) plant.
In general, combined cycle efficiencies in service are over 50% on a lower heating value and Gross Output basis.
Most combined cycle units, especially the larger units, have peak, steady-state efficiencies on the LHV basis of 55 to 59%.
A limitation of combined cycles is that efficiency is reduced when not running at continuous output. During start up, the second cycle can take time to start up. Thus efficiency is initially much lower until the second cycle is running, which can take an hour or more.
Fuel heating value | Combined cycle power plant | Wikipedia | 442 | 583901 | https://en.wikipedia.org/wiki/Combined%20cycle%20power%20plant | Technology | Power generation | null |
Heat engine efficiency can be based on the fuel Higher Heating Value (HHV), including latent heat of vaporisation that would be recuperated in condensing boilers, or the Lower Heating Value (LHV), excluding it.
The HHV of methane is , compared to a LHV: a 11% increase.
Boosting efficiency
Efficiency of the turbine is increased when combustion can run hotter, so the working fluid expands more. Therefore, efficiency is limited by whether the first stage of turbine blades can survive higher temperatures. Cooling and materials research are continuing. A common technique, adopted from aircraft, is to pressurise hot-stage turbine blades with coolant. This is also bled-off in proprietary ways to improve the aerodynamic efficiencies of the turbine blades. Different vendors have experimented with different coolants. Air is common but steam is increasingly used. Some vendors might now utilize single-crystal turbine blades in the hot section, a technique already common in military aircraft engines.
The efficiency of CCGT and GT can also be boosted by pre-cooling combustion air. This increases its density, also increasing the expansion ratio of the turbine. This is practised in hot climates and also has the effect of increasing power output. This is achieved by evaporative cooling of water using a moist matrix placed in the turbine's inlet, or by using Ice storage air conditioning. The latter has the advantage of greater improvements due to the lower temperatures available. Furthermore, ice storage can be used as a means of load control or load shifting since ice can be made during periods of low power demand and, potentially in the future the anticipated high availability of other resources such as renewables during certain periods.
Combustion technology is a proprietary but very active area of research, because fuels, gasification and carburation all affect fuel efficiency. A typical focus is to combine aerodynamic and chemical computer simulations to find combustor designs that assure complete fuel burn up, yet minimize both pollution and dilution of the hot exhaust gases. Some combustors inject other materials, such air or steam, to reduce pollution by reducing the formation of nitrates and ozone. | Combined cycle power plant | Wikipedia | 435 | 583901 | https://en.wikipedia.org/wiki/Combined%20cycle%20power%20plant | Technology | Power generation | null |
Another active area of research is the steam generator for the Rankine cycle. Typical plants already use a two-stage steam turbine, reheating the steam between the two stages. When the heat-exchangers' thermal conductivity can be improved, efficiency improves. As in nuclear reactors, tubes might be made thinner (e.g. from stronger or more corrosion-resistant steel). Another approach might use silicon carbide sandwiches, which do not corrode.
There is also some development of modified Rankine cycles. Two promising areas are ammonia/water mixtures, and turbines that utilize supercritical carbon dioxide.
Modern CCGT plants also need software that is precisely tuned to every choice of fuel, equipment, temperature, humidity and pressure. When a plant is improved, the software becomes a moving target. CCGT software is also expensive to test, because actual time is limited on the multimillion-dollar prototypes of new CCGT plants. Testing usually simulates unusual fuels and conditions, but validates the simulations with selected data points measured on actual equipment.
Competition
There is active competition to reach higher efficiencies.
Research aimed at turbine inlet temperature has led to even more efficient combined cycles.
Nearly 60% LHV efficiency (54% HHV efficiency) was reached in the Baglan Bay power station, using a GE H-technology gas turbine with a NEM 3 pressure reheat boiler, using steam from the heat recovery steam generator (HRSG) to cool the turbine blades.
In May 2011 Siemens AG announced they had achieved a 60.75% efficiency with a 578 megawatt SGT5-8000H gas turbine at the Irsching Power Station.
The Chubu Electric’s Nishi-ku, Nagoya power plant 405 MW 7HA is expected to have 62% gross combined cycle efficiency.
On April 28, 2016, the plant run by Électricité de France in Bouchain was certified by Guinness World Records as the world's most efficient combined cycle power plant at 62.22%. It uses a General Electric 9HA, that claimed 41.5% simple cycle efficiency and 61.4% in combined cycle mode, with a gas turbine output of 397 MW to 470 MW and a combined output of 592 MW to 701 MW. Its firing temperature is between , its overall pressure ratio is 21.8 to 1.
In December 2016, Mitsubishi claimed a LHV efficiency of greater than 63% for some members of its J Series turbines. | Combined cycle power plant | Wikipedia | 506 | 583901 | https://en.wikipedia.org/wiki/Combined%20cycle%20power%20plant | Technology | Power generation | null |
In December 2017, GE claimed 64% in its latest 826 MW HA plant, up from 63.7%. They said this was due to advances in additive manufacturing and combustion. Their press release said that they planned to achieve 65% by the early 2020s.
Integrated gasification combined cycle (IGCC)
An integrated gasification combined cycle, or IGCC, is a power plant using synthesis gas (syngas). Syngas can be produced from a number of sources, including coal and biomass. The system uses gas and steam turbines, the steam turbine operating from the heat left over from the gas turbine. This process can raise electricity generation efficiency to around 50%.
Integrated solar combined cycle (ISCC)
An Integrated Solar Combined Cycle (ISCC) is a hybrid technology in which a solar thermal field is integrated within a combined cycle plant. In ISCC plants, solar energy is used as an auxiliary heat supply, supporting the steam cycle, which results in increased generation capacity or a reduction of fossil fuel use.
Thermodynamic benefits are that daily steam turbine startup losses are eliminated.
Major factors limiting the load output of a combined cycle power plant are the allowed pressure and temperature transients of the steam turbine and the heat recovery steam generator waiting times to establish required steam chemistry conditions and warm-up times for the balance of plant and the main piping system. Those limitations also influence the fast start-up capability of the gas turbine by requiring waiting times. And waiting gas turbines consume gas. The solar component, if the plant is started after sunshine, or before, if there is heat storage, allows the preheat of the steam to the required conditions. That is, the plant is started faster and with less consumption of gas before achieving operating conditions. Economic benefits are that the solar components costs are 25% to 75% those of a Solar Energy Generating Systems plant of the same collector surface.
The first such system to come online was the Archimede combined cycle power plant, Italy in 2010, followed by Martin Next Generation Solar Energy Center in Florida, and in 2011 by the Kuraymat ISCC Power Plant in Egypt, Yazd power plant in Iran, Hassi R'mel in Algeria, Ain Beni Mathar in Morocco. In Australia CS Energy's Kogan Creek and Macquarie Generation's Liddell Power Station started construction of a solar Fresnel boost section (44 MW and 9 MW), but the projects never became active. | Combined cycle power plant | Wikipedia | 498 | 583901 | https://en.wikipedia.org/wiki/Combined%20cycle%20power%20plant | Technology | Power generation | null |
Bottoming cycles
In most successful combined cycles, the bottoming cycle for power is a conventional steam Rankine cycle.
It is already common in cold climates (such as Finland) to drive community heating systems from a steam power plant's condenser heat. Such cogeneration systems can yield theoretical efficiencies above 95%.
Bottoming cycles producing electricity from the steam condenser's heat exhaust are theoretically possible, but conventional turbines are uneconomically large. The small temperature differences between condensing steam and outside air or water require very large movements of mass to drive the turbines.
Although not reduced to practice, a vortex of air can concentrate the mass flows for a bottoming cycle. Theoretical studies of the Vortex engine show that if built at scale it is an economical bottoming cycle for a large steam Rankine cycle power plant.
Combined cycle hydrogen power plant
A combined cycle hydrogen power plant is a power plant that uses hydrogen in a combined cycle power plant. A green hydrogen combined cycle power plant is only about 40% efficient, after electrolysis and reburning for electricity, and is a viable option for energy storage for longer term compared to battery storage. Natural gas power plants could be converted to hydrogen power plants with minimal renovation or do a combined mix of natural gas and hydrogen.
Retrofitting natural gas power plants
Natural gas power plants could be designed with a transition to hydrogen in mind by having wider inlet pipes to the burner to increase flow rates because hydrogen is less dense than natural gas, and have the right material because hydrogen can cause hydrogen embrittlement.
Limitations
Current electrolysis plants are not capable of providing the scale of hydrogen that is needed to provide for a large scale power plant. On site electrolysis may be needed, then storing large amounts of hydrogen could take up a lot of space if it is only compressed hydrogen and not Liquid hydrogen. Hydrogen embrittlement could happen in pipelines, but 316L stainless steel pipelines could handle compressed hydrogen above 50 Bar (unit), which is what compressed natural gas is piped at, or wider pipelines could be built for hydrogen. Polyethylene or fiber-reinforced polymer pipelines coule also be used. | Combined cycle power plant | Wikipedia | 445 | 583901 | https://en.wikipedia.org/wiki/Combined%20cycle%20power%20plant | Technology | Power generation | null |
Nitrous oxide
When hydrogen is burned as a fuel no carbon dioxide is produced, but more nitrous oxide is produced because of the higher flame temperature from hydrogen, a selective catalytic reduction process could be implemented to break NO₂ down into just nitrogen and water. The exhaust from a burning hydrogen reaction is water vapor and could be used as a diluent to lower the high burning temp that creates the nitrous oxide.
Corrosion
Corrosion of the turbine from the water vapor from the hydrogen flame could reduce plant life or parts may need to be replaced more often.
Fuel handling
Hydrogen is the smallest and lightest element and can leak more easily at connection points and joints. Hydrogen diffuses quickly mitigating explosions. A hydrogen flame is also not as visible as a standard flame.
Transition to a renewable power grid
Wind and solar power are variable renewable energy sources that aren't as consistent as base load energy. Hydrogen could help renewables by capturing excess energy, with electrolysis, when they produce too much, and fill the gaps with that energy when they aren't producing as much. | Combined cycle power plant | Wikipedia | 219 | 583901 | https://en.wikipedia.org/wiki/Combined%20cycle%20power%20plant | Technology | Power generation | null |
Myriapods () are the members of subphylum Myriapoda, containing arthropods such as millipedes and centipedes. The group contains about 13,000 species, all of them terrestrial.
Although molecular evidence and similar fossils suggests a diversification in the Cambrian Period, the oldest known fossil record of myriapods dates between the Late Silurian and Early Devonian, with Pneumodesmus preserving the earliest known evidence of air-breathing on land. Other early myriapod fossil species around the similar time period include Kampecaris obanensis and Archidesmus sp. The phylogenetic classification of myriapods is still debated.
The scientific study of myriapods is myriapodology, and those who study myriapods are myriapodologists.
Anatomy
Myriapods have a single pair of antennae and, in most cases, simple eyes. Exceptions are the two classes of symphylans and pauropods, the millipede order Polydesmida and the centipede order Geophilomorpha, which are all eyeless. The house centipedes (Scutigera) on the other hand, have large and well-developed compound eyes. The mouthparts lie on the underside of the head, with an "epistome" and labrum forming the upper lip, and a pair of maxillae forming the lower lip. A pair of mandibles lie inside the mouth. Myriapods breathe through spiracles that connect to a tracheal system similar to that of insects. There is a long tubular heart that extends through much of the body, but usually few, if any, blood vessels.
Malpighian tubules excrete nitrogenous waste into the digestive system, which typically consists of a simple tube. Although the ventral nerve cord has a ganglion in each segment, the brain is relatively poorly developed. | Myriapoda | Wikipedia | 390 | 584096 | https://en.wikipedia.org/wiki/Myriapoda | Biology and health sciences | Myriapoda | null |
During mating, male myriapods produce a packet of sperm, or spermatophore, which they must transfer to the female externally; this process is often complex and highly developed. The female lays eggs which hatch as much-shortened versions of the adults, with only a few segments and as few as three pairs of legs. With the exception of the two centipede orders Scolopendromorpha and Geophilomorpha, which have epimorphic development (all body segments are formed segments embryonically), the young add additional segments and limbs as they repeatedly moult to reach the adult form.
The process of adding new segments during postembryonic growth is known as anamorphosis, of which there are three types: euanamorphosis, emianamorphosis, and teloanamorphosis. In euanamorphosis, every moult is followed by addition of new segments, even after reaching sexual maturity; in emianamorphosis, new segments are added until a certain stage, and further moults happen without addition of segments; and in teloanamorphosis, where the addition of new segments stops after the adult form is reached, after no further moults occur.
Ecology
Myriapods are most abundant in moist forests, where they fulfill an important role in breaking down decaying plant material, although a few live in grasslands, semi-arid habitats or even deserts. A very small percentage of species are littoral (found along the sea shore). The majority are detritivorous, with the exception of centipedes, which are chiefly nocturnal predators.
A few species of centipedes and millipedes are able to produce light and are therefore bioluminescent. Pauropodans and symphylans are small, sometimes microscopic animals that resemble centipedes superficially and live in soils. Millipedes differ from the other groups in having their body segments fused into pairs, giving the appearance that each segment bears two pairs of legs, while the other three groups have a single pair of legs on each body segment.
Although not generally considered dangerous to humans, many millipedes produce noxious secretions (often containing benzoquinones) which in rare cases can cause temporary blistering and discolouration of the skin. Large centipedes, however, can bite humans, and although the bite may cause intense pain and discomfort, fatalities are extremely rare. | Myriapoda | Wikipedia | 502 | 584096 | https://en.wikipedia.org/wiki/Myriapoda | Biology and health sciences | Myriapoda | null |
Classification
There has been much debate as to which arthropod group is most closely related to the Myriapoda. Under the Mandibulata hypothesis, Myriapoda is the sister taxon to Pancrustacea, a group comprising the Crustacea and Hexapoda (insects and their close relatives). Under the Atelocerata hypothesis, Hexapoda is the closest, whereas under the Paradoxopoda hypothesis, Chelicerata is the closest. This last hypothesis, although supported by few, if any, morphological characters, is supported by a number of molecular studies.
A 2020 study found numerous characters of the eye and preoral region suggesting that the closest relatives to crown myriapods are the extinct Euthycarcinoids. There are four classes of extant myriapods, Chilopoda (centipedes), Diplopoda, Pauropoda and Symphyla, containing a total of around 12,000 species. While each of these groups of myriapods is believed to be monophyletic, relationships among them are less certain.
Centipedes
Centipedes make up the class Chilopoda. They are fast, predatory and venomous, hunting mostly at night. There are around 3,300 species, ranging from the diminutive Nannarrup hoffmani (less than 12 mm or in in length) to the giant Scolopendra gigantea, which may exceed .
Millipedes | Myriapoda | Wikipedia | 301 | 584096 | https://en.wikipedia.org/wiki/Myriapoda | Biology and health sciences | Myriapoda | null |
Millipedes form the class Diplopoda. Most millipedes are slower than centipedes, and feed on leaf litter and detritus. Except for the first segment called collum, which don't have any appendages, and the next three segments with a single pair of legs each, they are distinguished by the fusion of each pair of body segments into a single unit, giving the appearance of having two pairs of legs per segment. It is also common for the sternites, pleurites and tergites to fuse into rigid armour rings. The males produce aflagellate sperm cells, unlike the rest of the myriapods which produce flagellated sperm. Around 12,000 species have been described, which may represent less than a tenth of the true global millipede diversity. Although the name "millipede" is a compound word formed from the Latin roots millia ("thousand") and pes (gen. pedis) ("foot"), millipedes typically have between 36 and 400 legs. In 2021, however, was described Eumillipes persephone, the first species known to have 1,000 or more legs, possessing 1,306 of them. Pill millipedes are much shorter, and are capable of rolling up into a ball, like pillbugs.
Symphyla
Symphylans, or garden centipedes, are closely related to centipedes and millipedes. They are 3 to 6 cm long, and have 6 to 12 pairs of legs, depending on their life stage. Their eggs, which are white and spherical and covered with small hexagonal ridges, are laid in batches of 4 to 25 at a time, and usually take up to 40 days to hatch. There are about 200 species worldwide.
Pauropoda
Pauropoda is another small group of small myriapods. They are typically 0.5–2.0 mm long and live in the soil on all continents except Antarctica. Over 700 species have been described. They are believed to be the sister group to millipedes, and have the dorsal tergites fused across pairs of segments, similar to the more complete fusion of segments seen in millipedes.
Arthropleuridea | Myriapoda | Wikipedia | 462 | 584096 | https://en.wikipedia.org/wiki/Myriapoda | Biology and health sciences | Myriapoda | null |
Arthropleurideans were ancient myriapods that are now extinct, known from the late Silurian to the Permian. The most famous members are from the genus Arthropleura, which was a giant, probably herbivorous, animal that could be up to long, but the group also includes species less than . Arthropleuridea was historically considered a distinct class of myriapods, but since 2000 scientific consensus has viewed the group as a subset of millipedes, although the relationship of arthropleurideans to other millipedes and to each other is debated.
Myriapod relationships
A variety of groupings (clades) of the myriapod classes have been proposed, some of which are mutually exclusive, and all of which represent hypotheses of evolutionary relationships. Traditional relationships supported by morphological similarities (anatomical or developmental similarities) are challenged by newer relationships supported by molecular evidence (including DNA sequence and amino acid similarities).
Dignatha (also called Collifera) is a clade consisting of millipedes and pauropods, and is supported by morphological similarities including the presence of a gnathochilarium (a modified jaw and plate apparatus) and a collum, a legless segment behind the head.
Trignatha (also called Atelopoda) is a grouping of centipedes and symphylans, united by similarities of mouthparts.
Edafopoda is a grouping of symphylans and pauropodans that is supported by shared genetic sequences, yet conflicts with Dignatha and Trignatha.
Pectinopoda consist of millipedes and centipedes, a classification that also supports Edafopoda.
Progoneata is a group encompassing millipedes, pauropods and symphylans while excluding centipedes. Shared features include reproductive openings (gonopores) behind the second body segment, and sensory hairs (trichobothria) with a bulb-like swelling. It is compatible with either Dignatha or Edafopoda. | Myriapoda | Wikipedia | 424 | 584096 | https://en.wikipedia.org/wiki/Myriapoda | Biology and health sciences | Myriapoda | null |
Acidobacteriota is a phylum of Gram-negative bacteria. Its members are physiologically diverse and ubiquitous, especially in soils, but are under-represented in culture.
Description
Members of this phylum are physiologically diverse, and can be found in a variety of environments including soil, decomposing wood, hot springs, oceans, caves, and metal-contaminated soils. The members of this phylum are particularly abundant in soil habitats representing up to 52% of the total bacterial community. Environmental factors such as pH and nutrients have been seen to drive Acidobacteriota dynamics. Many Acidobacteriota are acidophilic, including the first described member of the phylum, Acidobacterium capsulatum.
There is much that is unknown about Acidobacteria both in their form and function. Thus, this is a growing field of microbiology. Some of this uncertainty can be attributed to the difficulty with which these bacteria are grown in the laboratory. There has been recent success in propagation by using low concentrations of nutrients in combination with high amounts of CO2, yet, progress is still quite slow. These new methods have only allowed approximately 30% of subdivisions to have species documented.
Additionally, many of the samples sequenced do not have taxonomic names as they have not yet been fully characterized. This area of study is a very current topic, and scientific understanding is expected to grow and change as new information comes to light.
Other notable species are Holophaga foetida, Geothrix fermentans, Acanthopleuribacter pedis and Bryobacter aggregatus.
Since they have only recently been discovered and the large majority have not been cultured, the ecology and metabolism of these bacteria is not well understood. However, these bacteria may be an important contributor to ecosystems, since they are particularly abundant within soils. Members of subdivisions 1, 4, and 6 are found to be particularly abundant in soils.
As well as their natural soil habitat, unclassified subdivision 2 Acidobacteriota have also been identified as a contaminant of DNA extraction kit reagents, which may lead to their erroneous appearance in microbiota or metagenomic datasets. | Acidobacteriota | Wikipedia | 460 | 584598 | https://en.wikipedia.org/wiki/Acidobacteriota | Biology and health sciences | Gram-negative bacteria | Plants |
Members of subdivision 1 have been found to dominate in low pH conditions. Additionally, Acidobacteriota from acid mine drainage have been found to be more adapted to acidic pH conditions (pH 2-3) compared to Acidobacteriota from soils, potentially due to cell specialization and enzyme stability.
The G+C content of Acidobacteria genomes are consistent within their subdivisions - above 60% for group V fragments and roughly 10% lower for group III fragments.
The majority of Acidobacteriota are considered aerobes. There are some Acidobacteriota that are considered anaerobes within subdivision 8 and subdivision 23. It has been found that some strains of Acidobacteriota originating from soils have the genomic potential to respire oxygen at atmospheric and sub-atmospheric concentrations.
Members of the Acidobacteriota phylum have been considered oligotrophic bacteria due to high abundances in low organic carbon environments. However, the variation in this phylum may indicate that they may not have the same ecological strategy.
History
The first species, Acidobacterium capsulatum, of this phylum was discovered in 1991. However, Acidobacteriota were not recognized as a distinct clade until 1997, and were not recognized as a phylum until 2012. First genome was sequenced in 2006.
Subdivisions
In an effort to further classify Acidobacteria, 16S rRNA gene regions were sequenced from many different strains. These sequences lead to the formation of subdivisions within the phyla. Today, there are 26 accepted subdivisions recognized in the Ribosomal Database Project.
Much of this variety comes from populations of acidobacteria found in soils contaminated with uranium. Therefore, most of the known species in this phyla are concentrated in a few of the subdivisions, the largest being #1. Most of these microbes are aerobes, and they are all heterotrophic. Subdivision 1 contains 11 of the known genera in addition to the majority of the species that have been able to be cultivated thus far.
Within the 22 known genera, there are 40 conclusive species. The genera are divided amongst subdivisions 3, 4, 8, 10, 23, and 1. As the Acidobateria are a developing area of microbiology, it is hypothesized that these numbers will change drastically with further study.
Metabolism | Acidobacteriota | Wikipedia | 482 | 584598 | https://en.wikipedia.org/wiki/Acidobacteriota | Biology and health sciences | Gram-negative bacteria | Plants |
Carbon
Some members of subdivision 1 are able to use D-glucose, D-xylose, and lactose as carbon sources, but are unable to use fucose or sorbose. Members of subdivision 1 also contain enzymes such as galactosidases used in the breakdown of sugars. Members of subdivision 4 have been found to use chitin as a carbon source.
Despite the presence of genetic information generally known to encode for carbohydrate processing machinery in various genera of Acidobacteria, several experimental studies have demonstrated the inability to break down various polysaccharides.
Cellulose is the main component of plant cell walls and a seemingly opportune resource for carbon. However, only a single species across all subdivisions has been shown to process it, Telmactobacter bradus from subvision 1. Scientists note that it is much too early in their understanding of the field to draw conclusions about carbon processing in Acidobacteria, but believe that xylan degradation (a polysaccharide primarily found in the secondary cell wall of plants) currently appears to be the most universal carbon breakdown ability.
Researchers believe that an additional factor in the lack of understanding of carbon degradation by acidobacteria may stem from the present limited ability to provide adequate cultivation conditions. To study the natural behavior of these bacteria, they must grow and live in a controlled, observable environment. If such a habitat cannot be provided, recorded data cannot reliably report on the activity of the microbes in question. Therefore, the inconsistencies between genome sequence based predictions and observed carbon processes may be explained by present study methods.
Nitrogen
There has been no clear evidence that Acidobacteriota are involved in nitrogen-cycle processes such as nitrification, denitrification, or nitrogen fixation. However, Geothrix fermantans was shown to be able to reduce nitrate and contained the norB gene. The NorB gene was also identified in Koribacter verstailis and Solibacter usitatus. In addition, the presence of the nirA gene has been observed in members of subdivision 1. Additionally, to date, all genomes have been described to directly uptake ammonium via ammonium channel transporter family genes. Acidobacteriota can use both inorganic and organic nitrogen as their nitrogen sources. | Acidobacteriota | Wikipedia | 483 | 584598 | https://en.wikipedia.org/wiki/Acidobacteriota | Biology and health sciences | Gram-negative bacteria | Plants |
Phylogeny
The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature and National Center for Biotechnology Information. | Acidobacteriota | Wikipedia | 30 | 584598 | https://en.wikipedia.org/wiki/Acidobacteriota | Biology and health sciences | Gram-negative bacteria | Plants |
The Chlamydiota (synonym Chlamydiae) are a bacterial phylum and class whose members are remarkably diverse, including pathogens of humans and animals, symbionts of ubiquitous protozoa, and marine sediment forms not yet well understood. All of the Chlamydiota that humans have known about for many decades are obligate intracellular bacteria; in 2020 many additional Chlamydiota were discovered in ocean-floor environments, and it is not yet known whether they all have hosts. Historically it was believed that all Chlamydiota had a peptidoglycan-free cell wall, but studies in the 2010s demonstrated a detectable presence of peptidoglycan, as well as other important proteins.
Among the Chlamydiota, all of the ones long known to science grow only by infecting eukaryotic host cells. They are as small as or smaller than many viruses. They are ovoid in shape and stain Gram-negative. They are dependent on replication inside the host cells; thus, some species are termed obligate intracellular pathogens and others are symbionts of ubiquitous protozoa. Most intracellular Chlamydiota are located in an inclusion body or vacuole. Outside cells, they survive only as an extracellular infectious form.
These Chlamydiota can grow only where their host cells grow, and develop according to a characteristic biphasic developmental cycle. Therefore, clinically relevant Chlamydiota cannot be propagated in bacterial culture media in the clinical laboratory. They are most successfully isolated while still inside their host cells.
Of various Chlamydiota that cause human disease, the two most important species are Chlamydia pneumoniae, which causes a type of pneumonia, and Chlamydia trachomatis, which causes chlamydia. Chlamydia is the most common bacterial sexually transmitted infection in the United States, and 2.86 million chlamydia infections are reported annually.
History
Chlamydia-like disease affecting the eyes of people was first described in ancient Chinese and Egyptian manuscripts. A modern description of chlamydia-like organisms was provided by Halberstaedrrter and von Prowazek in 1907. | Chlamydiota | Wikipedia | 469 | 584732 | https://en.wikipedia.org/wiki/Chlamydiota | Biology and health sciences | Gram-negative bacteria | Plants |
Chlamydial isolates cultured in the yolk sacs of embryonating eggs were obtained from a human pneumonitis outbreak in the late 1920s and early 1930s, and by the mid-20th century, isolates had been obtained from dozens of vertebrate species. The term chlamydia (a cloak) appeared in the literature in 1945, although other names continued to be used, including Bedsonia, Miyagawanella, ornithosis-, TRIC-, and PLT-agents. In 1956, Chlamydia trachomatis was first cultured by Tang Fei-fan, though they were not yet recognized as bacteria.
Nomenclature
In 1966, Chlamydiota were recognized as bacteria and the genus Chlamydia was validated. The order Chlamydiales was created by Storz and Page in 1971. The class Chlamydiia was recently validly published. Between 1989 and 1999, new families, genera, and species were recognized. The phylum Chlamydiae was established in Bergey's Manual of Systematic Bacteriology. By 2006, genetic data for over 350 chlamydial lineages had been reported. Discovery of ocean-floor forms reported in 2020 involves new clades. In 2022 the phylum was renamed Chlamydiota.
Taxonomy and molecular signatures
The Chlamydiota currently contain eight validly named genera, and 14 genera. The phylum presently consist of two orders (Chlamydiales, Parachlamydiales) and nine families within a single class (Chlamydiia). Only four of these families are validly named (Chlamydiaceae, Parachlamydiaceae, Simkaniaceae, Waddliaceae) while five are described as families (Clavichlamydiaceae, Criblamydiaceae, Parilichlamydiaceae, Piscichlamydiaceae, and Rhabdochlamydiaceae). | Chlamydiota | Wikipedia | 413 | 584732 | https://en.wikipedia.org/wiki/Chlamydiota | Biology and health sciences | Gram-negative bacteria | Plants |
The Chlamydiales order as recently described contains the families Chlamydiaceae, and the Clavichlamydiaceae, while the new Parachlamydiales order harbors the remaining seven families. This proposal is supported by the observation of two distinct phylogenetic clades that warrant taxonomic ranks above the family level. Molecular signatures in the form of conserved indels (CSIs) and proteins (CSPs) have been found to be uniquely shared by each separate order, providing a means of distinguishing each clade from the other and supporting the view of shared ancestry of the families within each order. The distinctness of the two orders is also supported by the fact that no CSIs were found among any other combination of families.
Molecular signatures have also been found that are exclusive for the family Chlamydiaceae. The Chlamydiaceae originally consisted of one genus, Chlamydia, but in 1999 was split into two genera, Chlamydophila and Chlamydia. The genera have since 2015 been reunited where species belonging to the genus Chlamydophila have been reclassified as Chlamydia species.
However, CSIs and CSPs have been found specifically for Chlamydophila species, supporting their distinctness from Chlamydia, perhaps warranting additional consideration of two separate groupings within the family. CSIs and CSPs have also been found that are exclusively shared by all Chlamydia that are further indicative of a lineage independent from Chlamydophila, supporting a means to distinguish Chlamydia species from neighbouring Chlamydophila members.
Phylogenetics
The Chlamydiota form a unique bacterial evolutionary group that separated from other bacteria about a billion years ago, and can be distinguished by the presence of several CSIs and CSPs. The species from this group can be distinguished from all other bacteria by the presence of conserved indels in a number of proteins and by large numbers of signature proteins that are uniquely present in different Chlamydiae species. | Chlamydiota | Wikipedia | 408 | 584732 | https://en.wikipedia.org/wiki/Chlamydiota | Biology and health sciences | Gram-negative bacteria | Plants |
Reports have varied as to whether the Chlamydiota are related to the Planctomycetota or Spirochaetota. Genome sequencing, however, indicates that 11% of the genes in Protochlamydia amoebophila UWE25 and 4% in the Chlamydiaceae are most similar to chloroplast, plant, and cyanobacterial genes. Cavalier-Smith has postulated that the Chlamydiota fall into the clade Planctobacteria in the larger clade Gracilicutes. However, phylogeny and shared presence of CSIs in proteins that are lineage-specific indicate that the Verrucomicrobiota are the closest free-living relatives of these parasitic organisms. Comparison of ribosomal RNA genes has provided a phylogeny of known strains within Chlamydiota.
Human pathogens and diagnostics
Three species of Chlamydiota that commonly infect humans are described:
Chlamydia trachomatis, which causes the eye-disease trachoma and the sexually transmitted infection chlamydia
Chlamydophila pneumoniae, which causes a form of pneumonia
Chlamydophila psittaci, which causes psittacosis
The unique physiological status of the Chlamydiota including their biphasic lifecycle and obligation to replicate within a eukaryotic host has enabled the use of DNA analysis for chlamydial diagnostics. Horizontal transfer of genes is evident and complicates this area of research. In one extreme example, two genes encoding histone-like H1 proteins of eukaryotic origin have been found in the prokaryotic genome of C. trachomatis, an obligate intracellular pathogen.
Phylogeny
Taxonomy
The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN) and National Center for Biotechnology Information (NCBI) | Chlamydiota | Wikipedia | 403 | 584732 | https://en.wikipedia.org/wiki/Chlamydiota | Biology and health sciences | Gram-negative bacteria | Plants |
"Similichlamydiales" Pallen, Rodriguez-R & Alikhan 2022 [Hat2]
Family "Piscichlamydiaceae" Horn 2010
Family "Parilichlamydiaceae" Stride et al. 2013 ["Similichlamydiaceae" Pallen, Rodriguez-R & Alikhan 2022]
Order Chlamydiales Storz & Page 1971
Family "Actinochlamydiaceae" Steigen et al. 2013
Family "Criblamydiaceae" Thomas, Casson & Greub 2006
Family Chlamydiaceae Rake 1957 ["Clavichlamydiaceae" Horn 2011]
Family Parachlamydiaceae Everett, Bush & Andersen 1999
Family Rhabdochlamydiaceae Corsaro et al. 2009
Family Simkaniaceae Everett, Bush & Andersen 1999
Family Waddliaceae Rurangirwa et al. 1999 | Chlamydiota | Wikipedia | 181 | 584732 | https://en.wikipedia.org/wiki/Chlamydiota | Biology and health sciences | Gram-negative bacteria | Plants |
An optical coating is one or more thin layers of material deposited on an optical component such as a lens, prism or mirror, which alters the way in which the optic reflects and transmits light. These coatings have become a key technology in the field of optics. One type of optical coating is an anti-reflective coating, which reduces unwanted reflections from surfaces, and is commonly used on spectacle and camera lenses. Another type is the high-reflector coating, which can be used to produce mirrors that reflect greater than 99.99% of the light that falls on them. More complex optical coatings exhibit high reflection over some range of wavelengths, and anti-reflection over another range, allowing the production of dichroic thin-film filters.
Types of coating
The simplest optical coatings are thin layers of metals, such as aluminium, which are deposited on glass substrates to make mirror surfaces, a process known as silvering. The metal used determines the reflection characteristics of the mirror; aluminium is the cheapest and most common coating, and yields a reflectivity of around 88%-92% over the visible spectrum. More expensive is silver, which has a reflectivity of 95%-99% even into the far infrared, but suffers from decreasing reflectivity (<90%) in the blue and ultraviolet spectral regions. Most expensive is gold, which gives excellent (98%-99%) reflectivity throughout the infrared, but limited reflectivity at wavelengths shorter than 550 nm, resulting in the typical gold colour.
By controlling the thickness and density of metal coatings, it is possible to decrease the reflectivity and increase the transmission of the surface, resulting in a half-silvered mirror. These are sometimes used as "one-way mirrors". | Optical coating | Wikipedia | 353 | 584887 | https://en.wikipedia.org/wiki/Optical%20coating | Technology | Optical components | null |
The other major type of optical coating is the dielectric coating (i.e. using materials with a different refractive index to the substrate). These are constructed from thin layers of materials such as magnesium fluoride, calcium fluoride, and various metal oxides, which are deposited onto the optical substrate. By careful choice of the exact composition, thickness, and number of these layers, it is possible to tailor the reflectivity and transmitivity of the coating to produce almost any desired characteristic. Reflection coefficients of surfaces can be reduced to less than 0.2%, producing an antireflection (AR) coating. Conversely, the reflectivity can be increased to greater than 99.99%, producing a high-reflector (HR) coating. The level of reflectivity can also be tuned to any particular value, for instance to produce a mirror that reflects 90% and transmits 10% of the light that falls on it, over some range of wavelengths. Such mirrors are often used as beamsplitters, and as output couplers in lasers. Alternatively, the coating can be designed such that the mirror reflects light only in a narrow band of wavelengths, producing an optical filter.
The versatility of dielectric coatings leads to their use in many scientific optical instruments (such as lasers, optical microscopes, refracting telescopes, and interferometers) as well as consumer devices such as binoculars, spectacles, and photographic lenses.
Dielectric layers are sometimes applied over top of metal films, either to provide a protective layer (as in silicon dioxide over aluminium), or to enhance the reflectivity of the metal film. Metal and dielectric combinations are also used to make advanced coatings that cannot be made any other way. One example is the so-called "perfect mirror", which exhibits high (but not perfect) reflection, with unusually low sensitivity to wavelength, angle, and polarization.
Antireflection coatings
Antireflection coatings are used to reduce reflection from surfaces. Whenever a ray of light moves from one medium to another (such as when light enters a sheet of glass after travelling through air), some portion of the light is reflected from the surface (known as the interface) between the two media. | Optical coating | Wikipedia | 461 | 584887 | https://en.wikipedia.org/wiki/Optical%20coating | Technology | Optical components | null |
A number of different effects are used to reduce reflection. The simplest is to use a thin layer of material at the interface, with an index of refraction between those of the two media. The reflection is minimized when
,
where is the index of the thin layer, and and are the indices of the two media. The optimum refractive indices for multiple coating layers at angles of incidence other than 0° is given by Moreno et al. (2005).
Such coatings can reduce the reflection for ordinary glass from about 4% per surface to around 2%. These were the first type of antireflection coating known, having been discovered by Lord Rayleigh in 1886. He found that old, slightly tarnished pieces of glass transmitted more light than new, clean pieces due to this effect.
Practical antireflection coatings rely on an intermediate layer not only for its direct reduction of reflection coefficient, but also use the interference effect of a thin layer. If the layer's thickness is controlled precisely such that it is exactly one-quarter of the wavelength of the light in the layer (a quarter-wave coating), the reflections from the front and back sides of the thin layer will destructively interfere and cancel each other.
In practice, the performance of a simple one-layer interference coating is limited by the fact that the reflections only exactly cancel for one wavelength of light at one angle, and by difficulties finding suitable materials. For ordinary glass (n≈1.5), the optimum coating index is n≈1.23. Few useful substances have the required refractive index. Magnesium fluoride (MgF2) is often used, since it is hard-wearing and can be easily applied to substrates using physical vapour deposition, even though its index is higher than desirable (n=1.38). With such coatings, reflection as low as 1% can be achieved on common glass, and better results can be obtained on higher index media. | Optical coating | Wikipedia | 399 | 584887 | https://en.wikipedia.org/wiki/Optical%20coating | Technology | Optical components | null |
Further reduction is possible by using multiple coating layers, designed such that reflections from the surfaces undergo maximum destructive interference. By using two or more layers, broadband antireflection coatings which cover the visible range (400-700 nm) with maximum reflectivities of less than 0.5% are commonly achievable. Reflection in narrower wavelength bands can be as low as 0.1%. Alternatively, a series of layers with small differences in refractive index can be used to create a broadband antireflective coating by means of a refractive index gradient.
High-reflection coatings
High-reflection (HR) coatings work the opposite way to antireflection coatings. The general idea is usually based on the periodic layer system composed from two materials, one with a high index, such as zinc sulfide (n=2.32) or titanium dioxide (n=2.4), and one with a low index, such as magnesium fluoride (n=1.38) or silicon dioxide (n=1.49). This periodic system significantly enhances the reflectivity of the surface in the certain wavelength range called band-stop, whose width is determined by the ratio of the two used indices only (for quarter-wave systems), while the maximum reflectivity increases up to almost 100% with a number of layers in the stack. The thicknesses of the layers are generally quarter-wave (then they yield to the broadest high reflection band in comparison to the non-quarter-wave systems composed from the same materials), this time designed such that reflected beams constructively interfere with one another to maximize reflection and minimize transmission. The best of these coatings built-up from deposited dielectric lossless materials on perfectly smooth surfaces can reach reflectivities greater than 99.999% (over a fairly narrow range of wavelengths). Common HR coatings can achieve 99.9% reflectivity over a broad wavelength range (tens of nanometers in the visible spectrum range).
As for AR coatings, HR coatings are affected by the incidence angle of the light. When used away from normal incidence, the reflective range shifts to shorter wavelengths, and becomes polarization dependent. This effect can be exploited to produce coatings that polarize a light beam. | Optical coating | Wikipedia | 466 | 584887 | https://en.wikipedia.org/wiki/Optical%20coating | Technology | Optical components | null |
By manipulating the exact thickness and composition of the layers in the reflective stack, the reflection characteristics can be tuned to a particular application, and may incorporate both high-reflective and anti-reflective wavelength regions. The coating can be designed as a long- or short-pass filter, a bandpass or notch filter, or a mirror with a specific reflectivity (useful in lasers). For example, the dichroic prism assembly used in some cameras requires two dielectric coatings, one long-wavelength pass filter reflecting light below 500 nm (to separate the blue component of the light), and one short-pass filter to reflect red light, above 600 nm wavelength. The remaining transmitted light is the green component.
Extreme ultraviolet coatings
In the EUV portion of the spectrum (wavelengths shorter than about 30 nm) nearly all materials absorb strongly, making it difficult to focus or otherwise manipulate light in this wavelength range. Telescopes such as TRACE or EIT that form images with EUV light use multilayer mirrors that are constructed of hundreds of alternating layers of a high-mass metal such as molybdenum or tungsten, and a low-mass spacer such as silicon, vacuum deposited onto a substrate such as glass. Each layer pair is designed to have a thickness equal to half the wavelength of light to be reflected. Constructive interference between scattered light from each layer causes the mirror to reflect EUV light of the desired wavelength as would a normal metal mirror in visible light. Using multilayer optics it is possible to reflect up to 70% of incident EUV light (at a particular wavelength chosen when the mirror is constructed). | Optical coating | Wikipedia | 329 | 584887 | https://en.wikipedia.org/wiki/Optical%20coating | Technology | Optical components | null |
Transparent conductive coatings
Transparent conductive coatings are used in applications where it is important that the coating conduct electricity or dissipate static charge. Conductive coatings are used to protect the aperture from electromagnetic interference, while dissipative coatings are used to prevent the build-up of static electricity. Transparent conductive coatings are also used extensively to provide electrodes in situations where light is required to pass, for example in flat panel display technologies and in many photoelectrochemical experiments. A common substance used in transparent conductive coatings is indium tin oxide (ITO). ITO is not very optically transparent, however. The layers must be thin to provide substantial transparency, particularly at the blue end of the spectrum. Using ITO, sheet resistances of 20 to 10,000 ohms per square can be achieved. An ITO coating may be combined with an antireflective coating to further improve transmittance. Other TCOs (Transparent Conductive Oxides) include AZO (Aluminium doped Zinc Oxide), which offers much better UV transmission than ITO.
A special class of transparent conductive coatings applies to infrared films for theater-air military optics where IR transparent windows need to have (Radar) stealth (Stealth technology) properties. These are known as RAITs (Radar Attenuating / Infrared Transmitting) and include materials such as boron doped DLC (Diamond-like carbon).
Phase correction coatings
The multiple internal reflections in roof prisms cause a polarization-dependent phase-lag of the transmitted light, in a manner similar to a Fresnel rhomb. This must be suppressed by multilayer phase-correction coatings applied to one of the roof surfaces to avoid unwanted interference effects and a loss of contrast in the image. Dielectric phase-correction prism coatings are applied in a vacuum chamber with maybe 30 different superimposed vapor coating layers deposits, making it a complex production process. | Optical coating | Wikipedia | 395 | 584887 | https://en.wikipedia.org/wiki/Optical%20coating | Technology | Optical components | null |
In a roof prism without a phase-correcting coating, s-polarized and p-polarized light each acquire a different geometric phase as they pass through the upper prism. When the two polarized components are recombined, interference between the s-polarized and p-polarized light results in a different intensity distribution perpendicular to the roof edge as compared to that along the roof edge. This effect reduces contrast and resolution in the image perpendicular to the roof edge, producing an inferior image compared to that from a porro prism erecting system. This roof edge diffraction effect may also be seen as a diffraction spike perpendicular to the roof edge generated by bright points in the image. In technical optics, such a phase is also known as the Pancharatnam phase, and in quantum physics an equivalent phenomenon is known as the Berry phase.
This effect can be seen in the elongation of the Airy disk in the direction perpendicular to the crest of the roof as this is a diffraction from the discontinuity at the roof crest.
The unwanted interference effects are suppressed by vapour-depositing a special dielectric coating known as a phase-compensating coating on the roof surfaces of the roof prism. These phase-correction coating or P-coating on the roof surfaces was developed in 1988 by Adolf Weyrauch at Carl Zeiss Other manufacturers followed soon, and since then phase-correction coatings are used across the board in medium and high-quality roof prism binoculars. This coating corrects for the difference in geometric phase between s- and p-polarized light so both have effectively the same phase shift, preventing image-degrading interference.
From a technical point of view, the phase-correction coating layer does not correct the actual phase shift, but rather the partial polarization of the light that results from total reflection. Such a correction can always only be made for a selected wavelength and for a specific angle of incidence; however, it is possible to approximately correct a roof prism for polychromatic light by superimposing several layers. In this way, since the 1990s, roof prism binoculars have also achieved resolution values that were previously only achievable with porro prisms. The presence of a phase-correction coating can be checked on unopened binoculars using two polarization filters.
Fano-resonant optical coatings | Optical coating | Wikipedia | 485 | 584887 | https://en.wikipedia.org/wiki/Optical%20coating | Technology | Optical components | null |
Fano-resonant optical coatings (FROCs) represent a new category of optical coatings. FROCs exhibit the photonic Fano resonance by coupling a broadband nanocavity, which serves as the continuum, with a narrowband Fabry–Perot nanocavity, representing the discrete state. The interference between these two resonances manifests as an asymmetric Fano-resonance line-shape. FROCs are considered a separate category of optical coatings because they enjoy optical properties that cannot be reproduced using other optical coatings. Mainly, semi-transparent FROCs act as a beam splitting filter that reflects and transmits the same color, a property that cannot be achieved with transmission filters, dielectric mirrors, or semi-transparent metals.
FROCs enjoy remarkable structural coloring properties, as they can produce colors across a wide color gamut with both high brightness and high purity. Moreover, the dependence of color on the angle of incident light can be controlled through the dielectric cavity material, making FROCs adaptable for applications requiring either angle-independent or angle-dependent coloring. This includes decorative purposes and anti-counterfeit measures.
FROCs were used as both monolithic spectrum splitters and selective solar absorbers, which makes them suitable for hybrid solar-thermal energy generation. They can be designed to reflect specific wavelength ranges, aligning with the energy band gap of photovoltaic cells, while absorbing the remaining solar spectrum. This enables higher photovoltaic efficiency at elevated optical concentrations by reducing the photovoltaic's cell temperature. The reduced temperature also increases the cell's lifetime. Additionally, their low infrared emissivity minimizes thermal losses, increasing the system's overall optothermal efficiency.
Sources
Hecht, Eugene. Chapter 9, Optics, 2nd ed. (1990), Addison Wesley. .
I. Moreno, et al., "Thin-film spatial filters", Optics Letters, 30, 914–916 (2005), .
C. Clark, et al., "Two-color Mach 3 IR coating for TAMD systems", Proc. SPIE, vol. 4375, p. 307–314 (2001), . | Optical coating | Wikipedia | 456 | 584887 | https://en.wikipedia.org/wiki/Optical%20coating | Technology | Optical components | null |
The Toronto subway is a rapid transit system serving Toronto and the neighbouring city of Vaughan in Ontario, Canada, operated by the Toronto Transit Commission (TTC). The subway system is a rail network consisting of three heavy-capacity rail lines operating predominantly underground. three new lines are under construction: two light rail lines (one running mostly underground, the other running mostly at-grade) and one heavy rail line (running both underground and on elevated guideways).
In 1954, the TTC opened Canada's first underground rail line, then known as the "Yonge subway", under Yonge Street between Union Station and Eglinton Avenue with 12 stations. As of 2024, the network encompasses 70 stations and of route. In , the system had a ridership of , or about per weekday as of , making it the second-busiest rapid transit system in Canada in terms of daily ridership, behind the Montreal Metro. There are 60 stations under construction as part of three new lines, two light rail lines and one subway line, and two extensions to existing lines.
Overview
There are three operating rapid transit lines in Toronto:
Line 1 Yonge–University is the longest and busiest rapid transit line in the system. It opened as the Yonge subway in 1954 with a length of , and since then has grown to a length of . The modern line is U-shaped, having two northern terminalsat Vaughan Metropolitan Centre and Finchand its southern end at Union station in downtown Toronto.
Line 2 Bloor–Danforth, opened in 1966, runs parallel to Bloor Street and Danforth Avenue between Kipling station in Etobicoke and Kennedy station in Scarborough. Construction has started on a three-stop extension of Line 2 northeastward from Kennedy station to Sheppard Avenue and McCowan via Scarborough City Centre.
Line 4 Sheppard opened in 2002 running under Sheppard Avenue East eastwards from Sheppard–Yonge station on Line 1 to Don Mills station; it is the shortest rapid transit line in Toronto at a length of and the only one without any open sections. | Toronto subway | Wikipedia | 415 | 584946 | https://en.wikipedia.org/wiki/Toronto%20subway | Technology | Canada | null |
three new lines are under construction, two light rail lines and one subway line.
Line 5 Eglinton (also known as the Eglinton Crosstown LRT) is an under-construction light rail line along Eglinton Avenue, planned to run from Kennedy station in the east to Mount Dennis station in the west. The line will have 25 stations, 15 of which will be underground, while the remaining ten will be at-grade stops located in at the road's median. Construction began in 2011. The line was expected to be completed in 2024 at a cost of approximately $12billion, though it has since been delayed.
An extension of Line 5 westwards for to Renforth station is also under construction. The extension will have seven stations, four of which will be underground and two of which will be elevated. Construction began in 2022, and is scheduled for completion in the 2030s.
Line 6 Finch West (also known as the Finch West LRT) is an under-construction , 18-stop light rail line travelling from Finch West station on Line 1 Yonge–University to the North Campus of Humber College, located mainly in the median of Finch Avenue. Construction on Line 6 began in 2019. It was scheduled for completion within the first half of 2024, with an estimated cost of $1.2billion, though it has since been delayed.
Ontario Line is an under-construction subway line from Exhibition station to Science Centre station, providing a second rapid transit line through the Financial District and downtown core. The project evolved from the long-planned Downtown Relief Line, first proposed in the mid-1980s. The line is scheduled for completion in 2031 at a cost of $17 to $19 billion. Upon opening, the plan is to reassign the "Line 3" moniker formerly used by Line 3 Scarborough to the Ontario Line. | Toronto subway | Wikipedia | 378 | 584946 | https://en.wikipedia.org/wiki/Toronto%20subway | Technology | Canada | null |
Until July 2023, the TTC operated an elevated light metro service:
Line 3 Scarborough, originally known as the Scarborough RT, was an elevated medium-capacity (light metro) rail line serving the city's eponymous suburban district. It opened in 1985, running from Kennedy station to McCowan station via . It was the only rapid transit line in Toronto to use Intermediate Capacity Transit System (ICTS) technology. Because of maintenance difficulties (along with the Line 2 subway extension into Scarborough), Line 3 was to be decommissioned on November 19, 2023. However, it was decommissioned approximately four months early due to a derailment on July 24, 2023. Bus service replaced Line 3 and is scheduled to continue until the extension of Line 2 to Scarborough City Centre opens in 2030.
History
Timeline of openings and closings
Line 1 Yonge–University
Canada's first subway, the Yonge subway, opened in 1954 with a length of . The line ran under or parallel to Yonge Street between Eglinton Avenue and Union station. It replaced the Yonge streetcar line, Canada's first streetcar line. In 1963, the line was extended northwards from Union station under University Avenue to Bloor Street, where it would later connect with the Bloor–Danforth subway (opened in 1966) at the double-deck St. George station. In 1974, the Yonge Street portion of the line was extended from Eglinton station north to Finch station. The Spadina segment of the line was constructed north from St. George station initially to Wilson station in 1978, and in 1996 to Downsview station, renamed Sheppard West in 2017. Part of the Spadina segment runs in the median of Allen Road – an expressway formerly known as the Spadina Expressway – and crosses over Highway 401 on overpasses. Six decades of extensions gave the line a U-shaped route running from its two northern terminals (Finch and Vaughan Metropolitan Centre stations) and looping on its southern end at Union station. The latest extension from Sheppard West to opened on December 17, 2017, making the line long, over five times its original length.
Line 2 Bloor–Danforth | Toronto subway | Wikipedia | 439 | 584946 | https://en.wikipedia.org/wiki/Toronto%20subway | Technology | Canada | null |
Opened in 1966, the Bloor–Danforth subway runs east–west under or near Bloor Street and Danforth Avenue. It replaced the Bloor streetcar line (which also served Danforth Avenue). Initially, the subway line ran between Keele station and Woodbine station. In 1968, the line was extended west to Islington station and east to Warden station, and in 1980, it was further extended west to Kipling station and east to Kennedy station.
Line 3 Scarborough
Opened in 1985, Line 3 (originally the Scarborough RT) was a light metro line running from Kennedy station to McCowan station. The TTC started to construct the line to use Canadian Light Rail Vehicles. However, the TTC was forced to convert to the Intermediate Capacity Transit System technology because the provincial government threatened to cut funding to the TTC if it did not. This line was never extended, and in July 2023, the line was shut down pending its dismantling due to a derailment that resulted in injuries. It is set to be replaced with an extension of Line 2 to Sheppard Avenue and McCowan Road via Scarborough Town Centre.
Line 4 Sheppard
Opened in 2002, the Sheppard subway runs under Sheppard Avenue from Sheppard–Yonge station to Don Mills station. The line was under construction when a change in provincial government threatened to terminate the project, but Mel Lastman, the last mayor of the former City of North York (today part of Toronto), used his influence to save the project. Despite the construction of many high-rise residential buildings along the line since its opening, ridership remains low resulting in a subsidy of $10 per ride. The line was intended to be extended to Scarborough Centre station, but because of the low ridership and the cost of tunnelling, there was a plan to extend rapid transit eastwards from Don Mills station via a surface light rail line, the Sheppard East LRT. However, in April 2019, Premier Doug Ford announced that the provincial government would extend Line 4 Sheppard to McCowan Road at some unspecified time in the future, thus replacing the proposed Sheppard East LRT. Line 4 Sheppard is also the only subway line in Toronto not to have any open sections.
Line 5 Eglinton | Toronto subway | Wikipedia | 453 | 584946 | https://en.wikipedia.org/wiki/Toronto%20subway | Technology | Canada | null |
Metrolinx is funding the Line 5 Eglinton, a light rail line along Eglinton Avenue. From Mount Dennis in the west to Brentcliffe Road (east of Laird Drive), the line will run almost entirely underground where Eglinton Avenue is generally four to five lanes wide. From east of Brentcliffe Road to Kennedy station, the line will operate on the surface in a reserved median in the middle of Eglinton Avenue, where the street is at least six lanes wide. Building on the surface instead of tunnelling reduces the cost of construction on the eastern end of the line. The average speed of the line is expected to be ; as a comparison, the average speed of the heavy-rail Line 2 Bloor–Danforth is . The Eglinton line originated from Transit City, a plan sponsored by then–Toronto mayor David Miller, to expedite transit improvement by building several light rail lines through the lower density parts of the city. Of the light rail lines proposed, only the Eglinton and Finch West lines are under construction . Line 5 was expected to be completed in 2024, though it has since been delayed.
Line 6 Finch West
Line 6 Finch West, also known as the "Finch West LRT", is an under-construction line being built by Mosaic Transit Group along Finch Avenue. It is to be operated by the Toronto Transit Commission and was also part of the Transit City proposal announced on March 16, 2007. The , 18-stop line is to extend from Finch West station on Line 1 Yonge–University to the north campus of Humber Polytechnic (formerly Humber College). The line is forecast to carry about 14.6million rides a year or 40,000 a day by 2031. Construction on this line began in 2019. It was scheduled for completion in the first half of 2024, with an estimated cost of $1.2billion, though it has since been delayed.
Ontario Line | Toronto subway | Wikipedia | 397 | 584946 | https://en.wikipedia.org/wiki/Toronto%20subway | Technology | Canada | null |
Ontario Line is an under-construction subway line from Exhibition station to Science Centre station, providing a second rapid transit line through the Financial District and downtown core. Although a subway line along Queen Street was first proposed in the early 1900s, the Downtown Relief Line was first proposed in the mid-1980s. The Ontario Line project extends further west and north than previous proposals to serve more of the city. The line is scheduled for completion in 2031 at a cost of $17 to $19 billion. Upon opening, the plan is for the line is take the "Line 3" moniker formerly used by Line 3 Scarborough.
Major incidents
On March 27, 1963, there was an electrical short in a subway car's motor. The driver decided to continue operating the train, despite visible smoke in the affected car, until the train reached Union station. This decision resulted in the destruction of six subway cars and extensive damage to the tunnel and signal lines west of Union station. Following this incident, safety procedures involving electrical malfunctions and/or fire in subway trains, were revised to improve safety and reduce the likelihood of a similar incident occurring.
On October 14, 1976, arson caused the destruction of four subway cars and damage to Christie station, resulting in the closure of part of the Bloor–Danforth line for three days, and the bypassing of Christie station for some time afterwards for repairs.
On August 11, 1995, the TTC suffered the deadliest subway accident in Canadian history, known as the Russell Hill accident, on the Yonge–University line south of St. Clair West station. Halfway between St. Clair West and Dupont stations, a southbound Line 1 subway train hit the rear of a stationary train ahead of it. Three people died and 100 other people were injured, some of them seriously. This led to a major reorganization at the TTC, with more focus on maintaining a "state of good repair" (i.e., an increased emphasis on safety and maintenance of existing TTC capital/services) and less on expansion.
On July 24, 2023, the last car of a train on Line 3 Scarborough derailed south of Ellesmere station. There were 45 people on board, with five injuries reported. The TTC closed the line while the cause of the accident, which was not immediately apparent, was investigated. Though the TTC planned to close Line 3 in November 2023, it announced on August 24 that the line would not reopen.
Operations and procedures
Terminal station reversals and short turns | Toronto subway | Wikipedia | 508 | 584946 | https://en.wikipedia.org/wiki/Toronto%20subway | Technology | Canada | null |
The heavy-rail subway lines were built in multiple segments with multiple crossovers. These are typically used for reversals at terminal stations, and allow arriving and departing trains to cross to and from the station's farside platform. They are also used for short turning trains at some through stations in order to accommodate emergency and planned service suspensions. Planned service suspensions generally occur on weekends for planned maintenance activities that are impractical to perform overnight. There is only one regular short turn service that occurs during the morning rush hour on Line 1 Yonge–University when some northbound trains short turn at Glencairn station.
On Line 3 Scarborough, light metro trains were not able to switch direction except at the ends of the line as there were no intermediate crossovers between the two termini. Thus, no short turns on Line 3 were possible.
Door operation
The heavy-rail subway lines use either a one- or two-person crew. With two-person train operation, an on-board train guard at the rear of the train is responsible for opening and closing the subway car doors and making sure no one is trapped in a door as the train leaves a station. From the subway's inception in 1954 to 1991, the train guard notified patrons that the subway car doors were closing with two short blasts from a whistle. With one-person train operation (OPTO), one person operates the train as well as the doors. The TTC notes that modern technology now allows one person to safely operate the train and close the doors, and that OPTO is in use in many major cities with large subway systems such as the London Underground, the Paris Metro, the Chicago "L" and the Montreal Metro.
Initially, all the heavy-rail subway lines (1, 2 and 4) used two-person train operation. On October 9, 2016, Line 4 Sheppard was converted to OPTO. On August 1, 2021, the TTC tested OPTO on a portion of Line 1 on Sundays only. Effective November 21, 2021, the TTC introduced OPTO seven days per week on Line 1 between Vaughan Metropolitan Centre and St. George stations. Between St. George and Finch stations, the TTC continued using two-person train operation until the full conversion of the line to OPTO on November 20, 2022. From its opening in 1985 to its close in 2023, trains on Line 3 Scarborough were operated by one person. | Toronto subway | Wikipedia | 491 | 584946 | https://en.wikipedia.org/wiki/Toronto%20subway | Technology | Canada | null |
According to a 2020 survey conducted by the Amalgamated Transit Union Local 113, two-thirds of Torontonians surveyed opposed the TTC's plan to eliminate the train guard on Line 1, and three-quarters of Torontonians disapproved of the fact that the public was not consulted when train guards were removed from Line 4's daily operations in 2016, citing safety concerns, among other issues, as key reasons motivating their response.
In 1991, as a result of lawsuits, electronic chimes, in the form of a descending arpeggiated major triad and a flashing pair of orange lights above the doorway, added for the hearing impaired, were tested and gradually introduced system-wide during the 1990s. The Toronto Rocket trains use the same door chimes and flashing orange lights as the older trains do, and also plays the additional voice announcement, "Please stand clear of the doors". Those chimes have become synonymous with the TTC and Toronto in general to the point that the CBC Radio One local afternoon show, Here and Now, includes them in its theme music.
Entering a station
There are several basic procedures that need to be completed once a train has entered a station. On TTC's Line 2, several symbols of different colours are installed on the station wall for the crew to use as a reference in positioning the train in the platform. A red circle, located at the train exit end of the platform, should be directly in front of the train operator's cab window when the train is aligned properly. A green triangle, located at the opposite end of the platform, is provided as a reference to the train guard that shows that the train is correctly aligned. Before opening the train doors, the guard lowers the cab window and points their finger out the window toward the green triangle when the cab is lined up with the triangle. If the train is not lined up properly, the guard is not permitted to open the doors.
To operate the doors, the guard is first required to insert and turn a key. This action provides system control to the door control panel. The doors are then opened by pushing buttons. After the doors are opened, the guard is required to stick their head out the cab window to observe passengers boarding and exiting. The train doors remain open for at least 15 seconds. | Toronto subway | Wikipedia | 465 | 584946 | https://en.wikipedia.org/wiki/Toronto%20subway | Technology | Canada | null |
When the guard determines that boarding is complete, the doors are closed. Electronic chimes and flashing lights are turned on, then the automated announcement "please stand clear of the doors" is played over the train's public address system, and finally the doors are closed. The chimes provide a clear notification and warning to passengers that the doors are closing and are played before the automated announcement is played, because such announcements may not be heard when the station is crowded.
After the doors are closed, the guard provides a signal to the train operator that the train can proceed. The signal is in the form of a green light that turns on inside the operating cab. When the doors are closed, a light turns on in the operating cab. The guard is instructed to visually observe the platform while the train departs the station. The distance for this visual inspection is typically three car lengths. An orange triangle installed on the station wall indicates the location where the guard may stop observing the platform and pull their head back into the cab. This is done to ensure that no passengers are being dragged along by the train.
Platform markers
All staffed subway operations must verify that the train is properly berthed before the doors are opened. At each subway platform, a set of three platform markers are affixed onto the platform wall. The train operator and guard use them to position the train. | Toronto subway | Wikipedia | 272 | 584946 | https://en.wikipedia.org/wiki/Toronto%20subway | Technology | Canada | null |
The current platform markers used for Lines 1, 2, and 4 are as follows:
Circular red disk (Lines 1, 2, and 4)—This marker is typically mounted on the station platform wall to assist the train operator in positioning the train in the station. When the operator's window is aligned with the red disk, the train is properly berthed in the station.
Green triangle (Lines 1 and 2)—This marker is typically mounted on the station platform wall to indicate to the guard, who is positioned in the trailing car, that it is safe to open the doors. When the guard's window is aligned with this marker, the guard must confirm the stop position by physically pointing to the green triangle. If the guard cannot see the green triangle, they are not permitted to open the train doors.
Orange triangle (Lines 1 and 2)—This marker is typically mounted on the station platform wall to assist the guard, who is positioned in the trailing car, to observe the platform for the required distance as the train is moving to exit the station. When the guard sees this triangle, they can cease observations. The distance between the green and orange triangles is typically the length of three rail cars.
Prior to 2017, when subway guards operated the doors from the fifth car instead of the trailing car in the T1 trains on Line 2, different platform markers were used. The following markers have now fallen into disuse as a result of a March 2017 policy change that required all guards to work from the trailing car on Line 2:
Circular green disk (Line 2)—This marker was mounted on the station platform wall in front of the guard's window in the fifth car from the lead unit. It indicated to the guard that the train was properly berthed. The guard was required to point to the circle before opening the doors to confirm the stop position.
Circular orange disk (Line 2)—This marker was mounted on the station platform wall to indicate to the guard when they could cease train departure platform observations. At this point, the guard closed the cab window.
Service frequency
During rush hour, up to 65 trains are on Line 1 simultaneously, 45 trains on Line 2, and 4 trains on Line 4. During non-rush hour periods, there are 30–46 trains on Line 1 at any one time.
On weekdays and Saturdays, subway service runs from approximately 6:00am to 1:30am; Sunday service begins at 8:00am. Start times on holidays may vary.
Station announcements | Toronto subway | Wikipedia | 506 | 584946 | https://en.wikipedia.org/wiki/Toronto%20subway | Technology | Canada | null |
On January 8, 1995, train operators began to announce each stop over the train's speaker system as a result of pressure from advocacy groups for the visually impaired, but announcements were sporadic until the TTC began to enforce the policy circa 2005. Later, automated announcements were implemented under further pressure from the advocacy groups. All Toronto subway trains use an automated system to announce each station, which is played twice over the speaker system: when the train departs a station (e.g. "The next station is: Dufferin, Dufferin station") and when it arrives at the following station (e.g. "Arriving at: Dufferin, Dufferin station"). In addition, the TTC's Toronto Rocket subway trains provide visible and audible automatic stop announcements. Unlike the other trains, the Toronto Rocket trains also announce connections to other TTC subway lines, such as "Change for Line 2", and terminus stations, "This is a terminal station" where applicable. , they also announce, except at terminus stations, which side the train doors will open on at each stop based on the direction of train travel.
Winter operations
Switches and power rails are vulnerable to malfunction under extreme winter conditions such as heavy snow or freezing rain. During such events, the TTC runs "storm trains" overnight along subway lines to keep power rails clear of ice. The TTC also has trains to apply an anti-freeze to the power rail once freezing rain starts.
These precautions were also used on Line 3 Scarborough, which used two power rails. After reviewing operations during the winter of 2018–2019, the TTC decided to change its procedures for Line 3. Thus, about two hours before an expected storm, the TTC would decide whether to shut down Line 3 and replace it with bus service. Just before the storm of February 2, 2022, the TTC replaced all Line 3 trains with 25 buses.
To keep switches in the yards from freezing, crews use switch heaters and manually monitor them to ensure they stay in working order during winter storms. Workcars are run as storm trains within the yards to prevent ice from building up on the power rails. The TTC stores subway trains in tunnels along main lines rather than in exterior yards.
Stations | Toronto subway | Wikipedia | 455 | 584946 | https://en.wikipedia.org/wiki/Toronto%20subway | Technology | Canada | null |
The Toronto subway has 70 stations across three lines. Most stations are named for the nearest major arterial road crossed by the line in question. A few are named for major landmarks, such as shopping centres or transportation hubs, served by the station. The stations along the University Avenue section of Line 1 Yonge–University, in particular, are named entirely for landmarks and public institutions (, , and ) and major churches ( and ). All trains, except for short turns, stop at every station along their route and run the entire length of their line from terminus to terminus. Nearly all stations outside the central business district have terminals for local TTC bus routes and streetcar routes situated within their fare-paid areas. All regular TTC bus and streetcar routes permit free transfers both to and from connecting subway lines.
By December 23, 2016, Presto card readers had been installed in at least one priority subway station entrance across the TTC network. Throughout 2017 and into mid-2018, the remaining subway station entrances that still use legacy turnstiles (which were retrofitted with Presto readers between 2010 and 2015) and the "floor-to-ceiling" revolving turnstiles (found in automatic/secondary entrances, which do not have Presto readers on them) were replaced by the new Presto-equipped "glass-paddle" fare gates.
Accessibility
Most of the Toronto subway system was built before wheelchair access was a requirement under the Ontarians with Disabilities Act (ODA). However, all subway stations built since 1996 are equipped with elevators, and seventy percent (56 of 75) of Toronto's subway stations are now accessible following upgrade works to add elevators, wide fare gates, and access doors to the station. The figures include the stations on the closed Line 3 Scarborough.
In 2021, the TTC planned to make all of its stations accessible by 2025. By comparison, the Montreal Metro plans for all stations to be accessible by 2038, the Chicago "L" plans for all stations to be accessible in the 2030s, and the New York City Subway plans for 95 percent of stations to be accessible by 2055.
All TTC trains offer level boarding for customers with wheelchairs and other accessibility needs, with priority seating and dedicated wheelchair areas onboard each train. | Toronto subway | Wikipedia | 458 | 584946 | https://en.wikipedia.org/wiki/Toronto%20subway | Technology | Canada | null |
Cleanliness
The May 2010 TTC cleanliness audit of subway stations found that none of them meets the transit agency's highest standard for cleanliness and general state of repair. Only 21 stations scored in the 70- to 80-percent range in the TTC's cleanliness scale, a range described as "Ordinary Tidiness", while 45 fell in the 60- to 70-percent range achieving what the commission describes as "Casual Inattentiveness". The May audit was the third in a series of comprehensive assessments that began in 2009. The commission announced a "Cleaning Blitz" that would add 30 new temporary cleaners for the latter part of 2010 to address major issues and has other action plans that include more full-time cleaners, and new and more effective ways at addressing station cleanliness.
The TTC implemented stricter cleanliness protocols during the COVID-19 pandemic.
Design and public art
According to a 1991 CBC report, "aesthetics weren't really a priority" on Toronto's subway system, describing stations as "a series of bathrooms without plumbing". Since that time, Toronto's subway system has had over 40 pieces installed in various subway stations. More art appeared as new stations were built and older ones were renovated.
In 2004, USA Today said of the Sheppard subway line: "Despite the remarkable engineering feats of this metro, known as Sheppard Subway, [it is] the art covering walls, ceilings, and platforms of all five stations that stands out. Each station is 'a total art experience where artists have created imaginative environments, uniquely expressing themes of community, location, and heritage' through panoramic landscapes and ceramic wall murals."
Internet and mobile phone access
Wireless service implementation
In 2012, the TTC awarded a contract to BAI Communications Canada to design, build and maintain a celular and Wi-Fi system along Toronto subway lines. BAI agreed to pay $25million to the TTC over a 20-year period for the exclusive rights to provide the service. BAI in turn would sell access to the cellular system to other carriers. | Toronto subway | Wikipedia | 424 | 584946 | https://en.wikipedia.org/wiki/Toronto%20subway | Technology | Canada | null |
On December 13, 2013, Wi-Fi Internet access was launched at and St. George stations. The ad-supported service (branded as "TConnect") was provided by BAI Canada. The TTC and BAI Canada planned to offer TConnect at all underground stations. Commuters had to view a video advertisement to gain access to the Internet. It was expected that all of the 70 subway stations would have service by 2017, as well as the six stations along the Line 1 extension to Vaughan. From early December 2015 to late January 2016, users of TConnect were required to authenticate using a Twitter account, with Twitter's Canadian operations sponsoring the TConnect Wi-Fi network. Users of the network could sign in to enable an automatic Wi-Fi connection for 30 days. This arrangement was resumed on an optional basis from July 2016 to early December 2016. By August 2017, Wi-Fi was available at all existing stations and would be available in all future stations.
On June 17, 2015, the TTC announced that Wind Mobile (later rebranded Freedom Mobile) customers would be able to access cellular connectivity at some TTC subway stations. Service was initially between Bloor–Yonge and St. George stations on Line 1, and between Bloor–Yonge and Spadina stations on Line 2. Other carriers declined to use the BAI cellular system because of the price BAI was asking for access.
In April 2023, Rogers Communications took over BAI Communications and honoured existing access to Freedom Mobile customers. In August 2023, Rogers implemented 5G wireless service at all the TTC's downtown stations and within the tunnels between them. In September 2023, the federal government imposed new licence conditions requiring that cellphone and data services be available on the entire subway network by the end of 2026 and that all carriers, including Telus and Bell, were to have access to it. On October 2, 2023, Bell and Telus offered its cellular customers access to the subway's 5G system.
By November 2023, wireless service had been expanded to all TTC stations and to the tunnels between Sheppard West and Vaughan Metropolitan Centre stations, but only for Rogers and Freedom customers. Bell and Telus customers continued to have wireless service at a limited number of stations. In December 2023, Telus and Bell reached a deal with Rogers to provide their customers the same subway wireless services as Rogers and Freedom customers. | Toronto subway | Wikipedia | 491 | 584946 | https://en.wikipedia.org/wiki/Toronto%20subway | Technology | Canada | null |
Rogers and the TTC decided to end TConnect, the free public Wi-Fi service, on December 27, 2024, due to low usage and the cost of upgrading it.
Current wireless services
, Rogers 5G wireless service is available in all subway stations for customers of Rogers, Freedom Mobile, Telus and Bell, but service access between stations is limited. 5G wireless service is available in open sections, as well as between Bloor–Yonge and Dupont stations on Line 1, and between and Keele stations on Line 2. 5G service is also available in the tunnels between Sheppard West and Vaughan Metropolitan Centre stations. Wireless service is available to customers of Rogers, Freedom Mobile, Bell and Telus (including flanker brands of these companies such as Koodo and Virgin Plus). This wireless service is not free, and users require a subscription from one of the four aforementioned carriers, given the lack of subsidized wireless plans in Ontario.
Naming
The TTC considers multiple different factors when they name stations and stops for subway and LRT stations. They consider local landmarks, the cross streets of the station, distinct communities of the past and present in the vicinity of the station, names of other stations in the system, and the grade of the station.
Metrolinx uses five criteria for naming stations and stops. These are:
Simplicity
Names must be logical and relevant to the area the station is built in
Names should be relevant for the life of the station
Names should help passengers locate themselves within the region
Uniqueness
Metrolinx will use the word "stop" in place of "station" at 10 of the 25 stations along the first phase of Line 5, particularly those that are not grade-separated.
Rolling stock
The following table shows the vehicle type by line:
Heavy rail stock
Line 1 Yonge–University and Line 4 Sheppard operate using the newest version of Toronto's subway cars, the Toronto Rocket, while Line 2 Bloor–Danforth uses the older T1 subway trains. | Toronto subway | Wikipedia | 406 | 584946 | https://en.wikipedia.org/wiki/Toronto%20subway | Technology | Canada | null |
The TTC's original G-series cars were manufactured by the Gloucester Railway Carriage and Wagon Company. All subsequent heavy-rail subway cars were manufactured by Bombardier Transportation or one of its predecessors (Montreal Locomotive Works, Hawker Siddeley, and UTDC). All cars starting with the Hawker Siddeley H series in 1965 have been built in Bombardier's Thunder Bay, Ontario, plant. The final H4 subway cars were retired on January 27, 2012. This was followed by the retirement of the H5 subway cars, which had their final in-service trip on June 14, 2013, and the H6 retirement, which followed one year later with a final run on June 20, 2014.
Following the introduction of the Toronto Rocket trains on Lines 1 and 4, all the T1 trains were moved to Line 2. The T1s were expected to last until 2026. By the end of 2019, the TTC had proposed an overhaul to extend the T1 fleet's life by 10 years at an estimated cost of $100 million. By mid-2020, the TTC had started the design phase for a new generation of subway trains to replace the T1 fleet on Line 2 Bloor–Danforth. In late 2021, the TTC expected that the new trains would be introduced between 2026 and 2030, at an estimated cost of $1.6 billion. On October 13, 2022, the TTC issued a request for proposals to construct 480 new subway cars (80 six-car train sets) of a design different from the T1 and Toronto Rocket fleet for delivery between 2027 and 2033. , the TTC plans to overhaul the T1 fleet if newer trains cannot be delivered in time.
The Ontario Line will use smaller train sets and a smaller gauge than those used on the Toronto subway system. By using driverless trains with automatic train control (ATC), Metrolinx expects the line to be as frequent as the existing subway lines despite using smaller, lighter trains. In conjunction with ATC, stations will have platform-edge doors for safety, also allowing riders to exit and enter trains more quickly. The trains will be manufactured by Hitachi Rail, similar to trains in Copenhagen or Rome.
Light metro stock | Toronto subway | Wikipedia | 457 | 584946 | https://en.wikipedia.org/wiki/Toronto%20subway | Technology | Canada | null |
Line 3 Scarborough used 28 S-series trains built by the Urban Transportation Development Corporation (UTDC) in Millhaven, Ontario. These Intermediate Capacity Transit System (ICTS) trains were Mark I models, similar in design to the original trains found on the Vancouver SkyTrain and the Detroit People Mover. These were the original vehicles on the line and were in service from the line's opening in 1985 to its closure in 2023. Because of the trains' age, they were refurbished for operation and initially intended to last until the extension of Line 2 Bloor–Danforth was built. In February 2021, the TTC announced plans to accelerate the retirement of Line 3, intending to close it in 2023. This was due to delays in planning and construction of the Line 2 extension (which was then projected to open in 2030 at the earliest) along with the increasing difficulty of performing critical maintenance work on the trains. Following an initial temporary closure owing to a derailment in July 2023, the TTC decided in August 2023 not to reopen the line. The TTC proposed selling some of these trains to the Detroit People Mover, which uses a similar technology.
Light rail stock
Metrolinx plans to use 76 Bombardier Flexity Freedom low-floor, light-rail vehicles for Line 5 Eglinton; however, 44 Alstom Citadis Spirit vehicles may be used if Bombardier is unable to deliver the Flexity Freedom on time. Such a substitution would require modifications to Line 5, especially the maintenance facility, as the Citadis Spirit is longer than the Flexity Freedom. Metrolinx intends to use 17 Citadis Spirit vehicles on Line 6 Finch West instead of the Flexity Freedom.
Technology
The heavy rail and light metro lines have some characteristics in common: Such lines are fully isolated from road traffic and pedestrians; the station platforms are covered, and the trains are boarded through many doors from high platforms within a fare-paid zone separated by faregates.
In contrast, the surface portions of the light rail lines (Lines 5 and 6) will fit into the street environment. Light-rail tracks will be laid on the surface within reserved lanes in the middle of the street, and cross street intersections at grade. Surface stations will have simple, low-level platforms. However, like heavy rail and light metro, passengers will be able to board and alight the light rail trains by multiple doors. | Toronto subway | Wikipedia | 490 | 584946 | https://en.wikipedia.org/wiki/Toronto%20subway | Technology | Canada | null |
Line 3 Scarborough, a light metro, used a more complex technology than heavy rail, which a TTC document describes as follows:
Track is the 5 rail system on direct fixation and car is powered by an induction or "reaction rail" situated between the running rails at the same top of rail elevation. There are two side contacting power rails +300V and −300V respectively situated a distance of about 14 in. from the closest gauge line of one running rail.
Signals
Heavy rail
Fixed-block signalling was originally used on the Toronto subway since the opening of Toronto's first subway in 1954 and was the first signalling system used on Lines 2 and 4. As of 2022, Lines 2 and 4 use fixed-block signalling but Line 1 no longer does. Fixed-block signalling uses automatic signalling to prevent rear-end train collisions, while interlocking signals are used to prevent collisions from conflicting movements on track crossovers.
, automatic train control (ATC) has been implemented along the entire length of Line 1. In 2009, the TTC awarded a contract to Alstom to upgrade the signalling system of the existing section of Line 1, as well as equip its extension into Vaughan, with moving block–based communications-based train control (CBTC) by 2012. The estimated cost to implement ATC on Line 1 was $562million, $424million of which was funded by Metrolinx. The first section of the "Urbalis 400" ATC system on Line 1 entered revenue service on December 17, 2017, between Sheppard West and Vaughan stations, in conjunction with the opening of the Toronto–York Spadina subway extension (TYSSE) project.
The benefits of ATC on Line 1 are:
a reduced headway between trains from 2.5 minutes to 2 minutes during rush hours, allowing a 25 percent increase in the number of trains that can operate
fewer signal-related delays relative to the old fixed-block system
more efficient use of electricity, thus reducing operational costs
allowing single-track, bidirectional operation for trains in passenger service, albeit with reduced frequency, to allow for off-hour maintenance of the opposite track
The TTC has plans to convert Line 2 to ATC by 2030, subject to the availability of funding. | Toronto subway | Wikipedia | 463 | 584946 | https://en.wikipedia.org/wiki/Toronto%20subway | Technology | Canada | null |
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