text stringlengths 26 3.6k | page_title stringlengths 1 71 | source stringclasses 1
value | token_count int64 10 512 | id stringlengths 2 8 | url stringlengths 31 117 | topic stringclasses 4
values | section stringlengths 4 49 ⌀ | sublist stringclasses 9
values |
|---|---|---|---|---|---|---|---|---|
With overhead transmission lines, the propagation of lightning and switching surges can cause insulation failures into substation equipment. Line entrance surge arrestors are used to protect substation equipment accordingly. Insulation Coordination studies are carried out extensively to ensure equipment failure (and associated outages) is minimal.
Once past the switching components, the lines of a given voltage connect to one or more buses. These are sets of busbars, usually in multiples of three, since three-phase electrical power distribution is largely universal around the world.
The arrangement of switches, circuit breakers, and buses used affects the cost and reliability of the substation. For important substations a ring bus, double bus, or so-called "breaker and a half" setup can be used, so that the failure of any one circuit breaker does not interrupt power to other circuits, and so that parts of the substation may be de-energized for maintenance and repairs. Substations feeding only a single industrial load may have minimal switching provisions, especially for small installations.
Safety
Because of the risk of electrical shock, substations are inherently dangerous to electrical workers. To mitigate this hazard, substations are designed with various safety features. Live conductors and bare equipment are kept separate, either with protected equipment, or using screens or distance. Based on the jurisdiction or company, there are safety standards with minimum required clearance between different live equipment or conductors or between live metal and the ground, which often varies with higher clearance being required for higher voltages because of the greater ability to generate flashover. To this is added the necessary space for employees to work safely and vehicles to pass. Sometimes it is necessary to work on parts of the substation while energized, but employees must maintain a safe distance of at least . The aim to reduce substation footprints comes into conflict with ease of maintenance enhanced by including gaps where employees can safely work. | Substation | Wikipedia | 386 | 320217 | https://en.wikipedia.org/wiki/Substation | Technology | Electricity transmission and distribution | null |
Underneath a substation, a mat or grid of conductors laid around underground provides grounding. This grid, which is typically copper although it may be galvanized iron in some countries, is used to ground circuits that are being worked on to prevent accidental re-energization while workers are in contact with a de-energized circuit. Often, earth rods are driven deeper into the ground from the grounding grid for lower resistance grounding, and may be surrounded by bentonite or marconite to further reduce resistance and ensure effective grounding for the lifetime of the substation. Above ground, the grounding conductors may be steel, aluminum, or copper. They must be thick enough to carry the expected current of a fault for 1-3 seconds and remain undamaged. Substation fences, typically at least in height, both protect the public from electrical hazards and also protect the substation from vandalism. Internal fences can also be incorporated to protect employees from areas that are unsafe when energized.
Components
Substations generally have switching, protection and control equipment, and transformers. In a large substation, circuit breakers are used to interrupt any short circuits or overload currents that may occur on the network. Smaller distribution stations may use recloser circuit breakers or fuses for protection of distribution circuits. Substations themselves do not usually have generators, although a power plant may have a substation nearby. Other devices such as capacitors, voltage regulators, and reactors may also be located at a substation.
Substations may be on the surface in fenced enclosures, underground, or special-purpose buildings. High-rise buildings may have several indoor substations. Indoor substations are usually found in urban areas to reduce the noise from transformers, improve appearance, or protect switchgear from extreme climate or pollution.
Substations often use busbars as conductors between electrical equipment. Busbars may be aluminum tubing thick, or else wires (strain bus). | Substation | Wikipedia | 409 | 320217 | https://en.wikipedia.org/wiki/Substation | Technology | Electricity transmission and distribution | null |
Outdoor, above-ground substation structures include wood pole, lattice metal tower, and tubular metal structures, although other variants are available. Where space is plentiful and appearance of the station is not a factor, steel lattice towers provide low-cost supports for transmission lines and apparatus. Low-profile substations may be specified in suburban areas where appearance is more critical. Indoor substations may be gas insulated substations (GIS) (at high voltages, with gas insulated switchgear), or use metal-enclosed or metal-clad switchgear at lower voltages. Urban and suburban indoor substations may be finished on the outside so as to blend in with other buildings in the area.
A compact substation is generally an outdoor substation built in a metal enclosure, in which each item of the electrical equipment is located very near to each other to create a relatively smaller footprint size of the substation. | Substation | Wikipedia | 191 | 320217 | https://en.wikipedia.org/wiki/Substation | Technology | Electricity transmission and distribution | null |
Switchgear
High-voltage circuit breakers are commonly used to interrupt the flow of current in substation equipment. At the time of interruption, current could be normal, too high due to excessive load, unusual due to a fault, or tripped by protective relays prior to anticipated trouble. The most common technologies to extinguish the power arc from separating the conductors in the breaker include:
Air at atmospheric pressure (air-insulated switchgear (AIS)), which is the most common worldwide. Air is the cheapest insulator and is easy to modify, but AIS takes up more space, and leaves equipment exposed to the outside environment. One drawback of AIS is the visual impact of a larger substation with overhead power lines entering and exiting, which may be unacceptable in scenic or urban areas. AIS requires additional bracing in a seismically active area, and emits more electromagnetic fields and noise than alternative technologies.
Gas (gas circuit breaker (GCB) or gas-insulated switchgear (GIS)), most commonly sulfur hexafluoride (SF6) or a mixture of gases including SF6. Although it is the most expensive, these gases are a much more effective insulator than air. GIS require only 10 to 20 percent of the land area as AIS, which can save on land acquisition cost in urban areas, and allow the substation to be built at the exact location where its power is being used in an industrial or urban area—which can be a significant cost savings. On the generation side, GIS can be installed closer to the generator which allows cost savings in cabling, bus duct connections, and civil construction and can increase reliability. GIS can replace AIS if power requirements increase without requiring additional land area. Additionally, GIS is commonly installed in an enclosed building that keeps the equipment protected from pollution and salt. Unless the substation is often used for switching, maintenance cost can be very low or even zero for many years. Because SF6 turns to solid around , in some climates these circuit breakers require heaters to function in extremely cold weather. SF6 has been used in switchgear since the 1960s.
Mineral oil (called OCB for oil circuit breaker) provides a high resistance between the opened contacts, effectively stopping the flow of current. Although oil circuit breakers are suitable for a wide range of voltages, the oil becomes contaminated during the suppression of arcs and must be filtered or replaced periodically. | Substation | Wikipedia | 502 | 320217 | https://en.wikipedia.org/wiki/Substation | Technology | Electricity transmission and distribution | null |
Vacuum is a better insulator than air but less than gas or oil. Vacuum circuit breakers (VCB) are smaller than air circuit breakers and are commonly used in distribution and other switchgear under 35kv.
Mixed, including both gas and air insulation. Although it’s the least common option it can be useful when an air-insulated substation needs to be expanded but there is very limited location for additional construction. | Substation | Wikipedia | 87 | 320217 | https://en.wikipedia.org/wiki/Substation | Technology | Electricity transmission and distribution | null |
Reclosers are similar to breakers, and can be cheaper because they do not require separate protective relays. Often used in distribution, they often are programmed to trip when the amps exceed a certain amount over a period of time. Reclosers will attempt to re-energize the circuit after a delay. If unsuccessful for a few times, the recloser will have to be manually reset by an electrical worker.
Capacitors
Capacitor banks are used in substations to balance the lagging current draw from inductive loads (such as motors, transformers, and some industrial equipment) with their reactive load. Additional capacitor capacity may be needed if dispersed generation (such as small diesel generators, rooftop photovoltaic solar panels, or wind turbines) are added to the system. Capacitors can reduce the current in wires, helping stem system losses from voltage drop or enabling extra power to be sent through the conductors. Capacitors may be left on in response to constant inductive load or turned on when inductive load is increased, such as in the summer for air conditioners. The switching may be remote and can be done manually or automatically.
Control rooms
Larger substations have control rooms for the equipment used to monitor, control, and protect the rest of the substation equipment. It often contains protective relays, meters, breaker controls, communications, batteries, and recorders that save detailed data about substation operations, particularly when there is any unusual activity, to help reconstruct what happened after the fact. These control rooms typically are heated and air conditioned to ensure the reliable operation of this equipment. Additional equipment is necessary to handle power surges associated with intermittent renewable energy such as dispersed generation from wind or solar.
Transformers
Most transformers lose between 5 and 1.5 percent of their input as heat and noise. Iron losses are no-load and constant whenever the transformer is energized, while copper and auxiliary losses are proportionate to the square of the current. Auxiliary losses are due to running fans and pumps which is noisy when the transformer is operating at maximum capacity. To reduce noise, enclosures are often built around the transformer and can also be added after the substation is built.
Oil-based transformers are often built with bunded areas to prevent the escape of flaming or leaking oil. Fire separation areas or firewalls are built around the transformer to stop the spread of fire. Firefighting vehicles are allowed a path to access the area. | Substation | Wikipedia | 510 | 320217 | https://en.wikipedia.org/wiki/Substation | Technology | Electricity transmission and distribution | null |
Maintenance
Maintenance of substations involves inspections, data collection and analysis, and routine scheduled work. Using methods such as infrared scanning and dissolved gas analysis, it can be predicted when the substation will need maintenance and predict dangers before they materialize. Infrared technology finds hot spots in the substation where electrical energy is being converted to heat, which indicates a problem and can cause additional damage from the high heat. Dissolved gas analysis can tell when an oil-insulated transformer needs to have the oil filtered or replace, and also detect other issues.
Automation
Early electrical substations required manual switching or adjustment of equipment, and manual collection of data for load, energy consumption, and abnormal events. As the complexity of distribution networks grew, it became economically necessary to automate supervision and control of substations from a centrally attended point, to allow overall coordination in case of emergencies and to reduce operating costs. Early efforts to remote control substations used dedicated communication wires, often run alongside power circuits. Power-line carrier, microwave radio, fiber optic cables as well as dedicated wired remote control circuits have all been applied to Supervisory Control and Data Acquisition (SCADA) for substations. The development of the microprocessor made for an exponential increase in the number of points that could be economically controlled and monitored. Today, standardized communication protocols such as DNP3, IEC 61850 and Modbus, to list a few, are used to allow multiple intelligent electronic devices to communicate with each other and supervisory control centers. Distributed automatic control at substations is one element of the so-called smart grid. | Substation | Wikipedia | 323 | 320217 | https://en.wikipedia.org/wiki/Substation | Technology | Electricity transmission and distribution | null |
Crystal violet or gentian violet, also known as methyl violet 10B or hexamethyl pararosaniline chloride, is a triarylmethane dye used as a histological stain and in Gram's method of classifying bacteria. Crystal violet has antibacterial, antifungal, and anthelmintic (vermicide) properties and was formerly important as a topical antiseptic. The medical use of the dye has been largely superseded by more modern drugs, although it is still listed by the World Health Organization.
The name gentian violet was originally used for a mixture of methyl pararosaniline dyes (methyl violet), but is now often considered a synonym for crystal violet. The name refers to its colour, being like that of the petals of certain gentian flowers; it is not made from gentians or violets.
Production
A number of possible routes can be used to prepare crystal violet. The original procedure developed by the German chemists Kern and Caro involved the reaction of dimethylaniline with phosgene to give 4,4′-bis(dimethylamino)benzophenone (Michler's ketone) as an intermediate. This was then reacted with additional dimethylaniline in the presence of phosphorus oxychloride and hydrochloric acid.
The dye can also be prepared by the condensation of formaldehyde and dimethylaniline to give a leuco dye:
CH2O + 3 C6H5N(CH3)2 → CH(C6H4N(CH3)2)3 + H2O
Second, this colourless compound is oxidized to the coloured cationic form (hereafter with oxygen, but a typical oxidizing agent is manganese dioxide, MnO2):
CH(C6H4N(CH3)2)3 + HCl + O2 → [C(C6H4N(CH3)2)3]Cl + H2O
Dye colour | Crystal violet | Wikipedia | 421 | 1506024 | https://en.wikipedia.org/wiki/Crystal%20violet | Physical sciences | Organic salts | Chemistry |
When dissolved in water, the dye has a blue-violet colour with an absorbance maximum at 590 nm and an extinction coefficient of 87,000 M−1 cm−1. The colour of the dye depends on the acidity of the solution. At a pH of +1.0, the dye is green with absorption maxima at 420 nm and 620 nm, while in a strongly acidic solution (pH −1.0), the dye is yellow with an absorption maximum at 420 nm.
The different colours are a result of the different charged states of the dye molecule. In the yellow form, all three nitrogen atoms carry a positive charge, of which two are protonated, while the green colour corresponds to a form of the dye with two of the nitrogen atoms positively charged. At neutral pH, both extra protons are lost to the solution, leaving only one of the nitrogen atoms positive charged. The pKa for the loss of the two protons are approximately 1.15 and 1.8.
In alkaline solutions, nucleophilic hydroxyl ions attack the electrophilic central carbon to produce the colourless triphenylmethanol or carbinol form of the dye. Some triphenylmethanol is also formed under very acidic conditions when the positive charges on the nitrogen atoms lead to an enhancement of the electrophilic character of the central carbon, which allows the nucleophilic attack by water molecules. This effect produces a slight fading of the yellow colour.
Applications
Industry
Crystal violet is used as a textile and paper dye, and is a component of navy blue and black inks for printing, ball-point pens, and inkjet printers. Historically, it was the most common dye used in early duplication machines, such as the mimeograph and the ditto machine. It is sometimes used to colourize diverse products such as fertilizer, antifreeze, detergent, and leather. Marking blue, used to mark out pieces in metalworking, is composed of methylated spirits, shellac, and gentian violet. | Crystal violet | Wikipedia | 419 | 1506024 | https://en.wikipedia.org/wiki/Crystal%20violet | Physical sciences | Organic salts | Chemistry |
Science
When conducting DNA gel electrophoresis, crystal violet can be used as a nontoxic DNA stain as an alternative to fluorescent, intercalating dyes such as ethidium bromide. Used in this manner, it may be either incorporated into the agarose gel or applied after the electrophoresis process is finished. Used at a 10 ppm concentration and allowed to stain a gel after electrophoresis for 30 minutes, it can detect as little as 16 ng of DNA. Through use of a methyl orange counterstain and a more complex staining method, sensitivity can be improved further to 8 ng of DNA. When crystal violet is used as an alternative to fluorescent stains, it is not necessary to use ultraviolet illumination; this has made crystal violet popular as a means of avoiding UV-induced DNA destruction when performing DNA cloning in vitro.
In biomedical research, crystal violet can be used to stain the nuclei of adherent cells. In this application, crystal violet works as an intercalating dye and allows the quantification of DNA which is proportional to the number of cells.
The dye is used as a histological stain, particularly in Gram staining for classifying bacteria.
In forensics, crystal violet was used to develop fingerprints.
Crystal violet is also used as a tissue stain in the preparation of light microscopy sections. In laboratory, solutions containing crystal violet and formalin are often used to simultaneously fix and stain cells grown in tissue culture to preserve them and make them easily visible, since most cells are colourless. It is also sometimes used as a cheap way to put identification markings on laboratory mice; since many strains of lab mice are albino, the purple colour stays on their fur for several weeks.
Crystal violet can be used as an alternative to Coomassie brilliant blue (CBB) in staining of proteins separated by SDS-PAGE, reportedly showing a 5x improved sensitivity vs CBB. | Crystal violet | Wikipedia | 395 | 1506024 | https://en.wikipedia.org/wiki/Crystal%20violet | Physical sciences | Organic salts | Chemistry |
Medical
Gentian violet has antibacterial, antifungal, antihelminthic, antitrypanosomal, antiangiogenic, and antitumor properties. It is used medically for these properties, in particular for dentistry, and is also known as "pyoctanin" (or "pyoctanine"). It is commonly used for:
Marking the skin for surgery preparation and allergy testing;
Treating Candida albicans and related fungal infections, such as thrush, yeast infections, various types of tinea (ringworm, athlete's foot, jock itch);
Treating impetigo; it was used primarily before the advent of antibiotics, but still useful to persons who may be allergic to penicillin.
In resource-limited settings, gentian violet is used to manage burn wounds, inflammation of the umbilical cord stump (omphalitis) in the neonatal period, oral candidiasis in HIV-infected patients and mouth ulcers in children with measles.
In body piercing, gentian violet is commonly used to mark the location for placing piercings, including surface piercings.
Veterinary
Because of its antimicrobial activity, it is used to treat ich in fish. However, it usually is illegal to use in fish intended for human consumption.
History
Synthesis
Crystal violet is one of the components of methyl violet, a dye first synthesized by Charles Lauth in 1861. From 1866, methyl violet was manufactured by the Saint-Denis-based firm of Poirrier et Chappat and marketed under the name "Violet de Paris". It was a mixture of the tetra-, penta- and hexamethylated pararosanilines.
Crystal violet itself was first synthesized in 1883 by (1850–1893) working in Basel at the firm of Bindschedler & Busch. To optimize the difficult synthesis which used the highly toxic phosgene, Kern entered into a collaboration with the German chemist Heinrich Caro at BASF. Kern also found that by starting with diethylaniline rather than dimethylaniline, he could synthesize the closely related violet dye now known as C.I. 42600 or C.I. Basic violet 4. | Crystal violet | Wikipedia | 459 | 1506024 | https://en.wikipedia.org/wiki/Crystal%20violet | Physical sciences | Organic salts | Chemistry |
Gentian violet
The name "gentian violet" (or Gentianaviolett in German) is thought to have been introduced by the German pharmacist Georg Grübler, who in 1880 started a company in Leipzig that specialized in the sale of staining reagents for histology. The gentian violet stain marketed by Grübler probably contained a mixture of methylated pararosaniline dyes. The stain proved popular and in 1884 was used by Hans Christian Gram to stain bacteria. He credited Paul Ehrlich for the aniline-gentian violet mixture. Grübler's gentian violet was probably very similar, if not identical, to Lauth's methyl violet, which had been used as a stain by Victor André Cornil in 1875.
Although the name gentian violet continued to be used for the histological stain, the name was not used in the dye and textile industries. The composition of the stain was not defined and different suppliers used different mixtures. In 1922, the Biological Stain Commission appointed a committee chaired by Harold Conn to look into the suitability of the different commercial products. In his book Biological Stains, Conn describes gentian violet as a "poorly defined mixture of violet rosanilins".
The German ophthalmologist Jakob Stilling is credited with discovering the antiseptic properties of gentian violet. He published a monograph in 1890 on the bactericidal effects of a solution that he christened "pyoctanin", which was probably a mixture of aniline dyes similar to gentian violet. He set up a collaboration with E. Merck & Co. to market "Pyoktanin caeruleum" as an antiseptic.
In 1902, Drigalski and Conradi found that although crystal violet inhibited the growth of many bacteria, it has little effect on Bacillus coli (Escherichia coli) and Bacillus typhi (Salmonella typhi), which are both gram-negative bacteria. A much more detailed study of the effects of Grübler's gentian violet on different strains of bacteria was published by John Churchman in 1912. He found that most gram-positive bacteria (tainted) were sensitive to the dye, while most gram-negative bacteria (not tainted) were not, and observed that the dye tended to act as a bacteriostatic agent rather than a bactericide. | Crystal violet | Wikipedia | 499 | 1506024 | https://en.wikipedia.org/wiki/Crystal%20violet | Physical sciences | Organic salts | Chemistry |
Precautions
One study in mice demonstrated dose-related carcinogenic potential at several different organ sites. The Food and Drug Administration in the US (FDA) has determined that gentian violet has not been shown by adequate scientific data to be safe for use in animal feed. Use of gentian violet in animal feed causes the feed to be adulterated and is a violation of the Federal Food, Drug, and Cosmetic Act in the US. On June 28, 2007, the FDA issued an "import alert" on farm raised seafood from China because unapproved antimicrobials, including gentian violet, had been consistently found in the products. The FDA report states:
"Like MG (malachite green), CV (crystal violet) is readily absorbed into fish tissue from water exposure and is reduced metabolically by fish to the leuco moiety, leucocrystal violet (LCV). Several studies by the National Toxicology Program reported the carcinogenic and mutagenic effects of crystal violet in rodents. The leuco form induces renal, hepatic and lung tumor in mice."
In 2019, Health Canada found medical devices that use gentian violet to be safe for use but recommended to stop using all drug products that contain gentian violet, including on animals, causing Canadian engineering schools to revisit the usage of this dye during orientation. | Crystal violet | Wikipedia | 279 | 1506024 | https://en.wikipedia.org/wiki/Crystal%20violet | Physical sciences | Organic salts | Chemistry |
In biology, the epigenome of an organism is the collection of chemical changes to its DNA and histone proteins that affects when, where, and how the DNA is expressed; these changes can be passed down to an organism's offspring via transgenerational epigenetic inheritance. Changes to the epigenome can result in changes to the structure of chromatin and changes to the function of the genome. The human epigenome, including DNA methylation and histone modification, is maintained through cell division (both mitosis and meiosis). The epigenome is essential for normal development and cellular differentiation, enabling cells with the same genetic code to perform different functions. The human epigenome is dynamic and can be influenced by environmental factors such as diet, stress, and toxins.
The epigenome is involved in regulating gene expression, development, tissue differentiation, and suppression of transposable elements. Unlike the underlying genome, which remains largely static within an individual, the epigenome can be dynamically altered by environmental conditions.
Types
The main types of epigenetic changes include:
DNA methylation
Addition of a methyl group to the DNA molecule, typically at cytosine bases. This modification generally leads to gene silencing by preventing the binding of transcription factors and other proteins necessary for gene expression.
DNA functionally interacts with a variety of epigenetic marks, such as cytosine methylation, also known as 5-methylcytosine (5mC). This epigenetic mark is widely conserved and plays major roles in the regulation of gene expression, in the silencing of transposable elements and repeat sequences.
Individuals differ with their epigenetic profile, for example the variance in CpG methylation among individuals is about 42%. On the contrary, epigenetic profile (including methylation profile) of each individual is constant over the course of a year, reflecting the constancy of our phenotype and metabolic traits. Methylation profile, in particular, is quite stable in a 12-month period and appears to change more over decades. | Epigenome | Wikipedia | 425 | 1506087 | https://en.wikipedia.org/wiki/Epigenome | Biology and health sciences | Genetics | Biology |
Methylation sites
CoRSIVs are Correlated Regions of Systemic Interindividual Variation in DNA methylation. They span only 0.1% of the human genome, so they are very rare; they can be inter-correlated over long genomic distances (>50 kbp). CoRSIVs are also associated with genes involved in a lot of human disorders, including tumors, mental disorders and cardiovascular diseases. It has been observed that disease-associated CpG sites are 37% enriched in CoRSIVs compared to control regions and 53% enriched in CoRSIVs relative to tDMRs (tissue specific Differentially Methylated Regions).
Most of the CoRSIVs are only 200 – 300 bp long and include 5–10 CpG dinucleotides, the largest span several kb and involve hundreds of CpGs. These regions tend to occur in clusters and the two genomic areas of high CoRSIV density are observed at the major histocompatibility (MHC) locus on chromosome 6 and at the pericentromeric region on the long arm of chromosome 20.
CoRSIVs are enriched in intergenic and quiescent regions (e.g. subtelomeric regions) and contain many transposable elements, but few CpG islands (CGI) and transcription factor binding sites. CoRSIVs are under-represented in the proximity of genes, in heterochromatic regions, active promoters, and enhancers. They are also usually not present in highly conserved genomic regions.
CoRSIVs can have a useful application: measurements of CoRSIV methylation in one tissue can provide some information about epigenetic regulation in other tissues, indeed we can predict the expression of associated genes because systemic epigenetic variants are generally consistent in all tissues and cell types. | Epigenome | Wikipedia | 373 | 1506087 | https://en.wikipedia.org/wiki/Epigenome | Biology and health sciences | Genetics | Biology |
Factors affecting methylation pattern
Quantification of the heritable basis underlying population epigenomic variation is also important to delineate its cis- and trans-regulatory architecture. In particular, most studies state that inter-individual differences in DNA methylation are mainly determined by cis-regulatory sequence polymorphisms, probably involving mutations in TFBSs (Transcription Factor Binding Sites) with downstream consequences on local chromatin environment. The sparsity of trans-acting polymorphisms in humans suggests that such effects are highly deleterious. Indeed, trans-acting factors are expected to be caused by mutations in chromatin control genes or other highly pleiotropic regulators. If trans-acting variants do exist in human populations, they probably segregate as rare alleles or originate from somatic mutations and present with clinical phenotypes, as is the case in many cancers.
Correlation between methylation and gene expression
DNA methylation (in particular in CpG regions) is able to affect gene expression: hypermethylated regions tend to be differentially expressed. In fact, people with a similar methylation profile tend to also have the same transcriptome. Moreover, one key observation from human methylation is that most functionally relevant changes in CpG methylation occur in regulatory elements, such as enhancers.
Anyway, differential expression concerns only a slight number of methylated genes: only one fifth of genes with CpG methylation shows variable expression according to their methylation state. It is important to notice that methylation is not the only factor affecting gene regulation.
Methylation in embryos
It was revealed by immunostaining experiments that in human preimplantation embryos there is a global DNA demethylation process. After fertilisation, the DNA methylation level decreases sharply in the early pronuclei. This is a consequence of active DNA demethylation at this stage. But global demethylation is not an irreversible process, in fact de novo methylation occurring from the early to mid-pronuclear stage and from the 4-cell to the 8-cell stage. | Epigenome | Wikipedia | 436 | 1506087 | https://en.wikipedia.org/wiki/Epigenome | Biology and health sciences | Genetics | Biology |
The percentage of DNA methylation is different in oocytes and in sperm: the mature oocyte has an intermediate level of DNA methylation (72%), instead the sperm has high level of DNA methylation (86%). Demethylation in paternal genome occurs quickly after fertilisation, whereas the maternal genome is quite resistant at the demethylation process at this stage. Maternal different methylated regions (DMRs) are more resistant to the preimplantation demethylation wave.
CpG methylation is similar in germinal vesicle (GV) stage, intermediate metaphase I (MI) stage and mature metaphase II (MII) stage. Non-CpG methylation continues to accumulate in these stages.
Chromatin accessibility in germline was evaluated by different approaches, like scATAC-seq and sciATAC-seq, scCOOL-seq, scNOMe-seq and scDNase-seq. Stage-specific proximal and distal regions with accessible chromatin regions were identified. Global chromatin accessibility is found to gradually decrease from the zygote to the 8-cell stage and then increase. Parental allele-specific analysis shows that paternal genome becomes more open than the maternal genome from the late zygote stage to the 4-cell stage, which may reflect decondensation of the paternal genome with replacement of protamines by histones.
Sequence-Dependent Allele-Specific Methylation
DNA methylation imbalances between homologous chromosomes show sequence-dependent behavior. Difference in the methylation state of neighboring cytosines on the same chromosome occurs due to the difference in DNA sequence between the chromosomes. Whole-genome bisulfite sequencing (WGBS) is used to explore sequence-dependent allele-specific methylation (SD-ASM) at a single-chromosome resolution level and comprehensive whole-genome coverage. The results of WGBS tested on 49 methylomes revealed CpG methylation imbalances exceeding 30% differences in 5% of the loci.
On the sites of gene regulatory loci bound by transcription factors the random switching between methylated and unmethylated states of DNA was observed. This is also referred as stochastic switching and it is linked to selective buffering of gene regulatory circuit against mutations and genetic diseases. Only rare genetic variants show the stochastic type of gene regulation. | Epigenome | Wikipedia | 506 | 1506087 | https://en.wikipedia.org/wiki/Epigenome | Biology and health sciences | Genetics | Biology |
The study made by Onuchic et al. was aimed to construct the maps of allelic imbalances in DNA methylation, gene transcription, and also of histone modifications. 36 cell and tissue types from 13 participant donors were used to examine 71 epigenomes. The results of WGBS tested on 49 methylomes revealed CpG methylation imbalances exceeding 30% differences in 5% of the loci. The stochastic switching occurred at thousands of heterozygous regulatory loci that were bound to transcription factors. The intermediate methylation state is referred to the relative frequencies between methylated and unmethylated epialleles. The epiallele frequency variations are correlated with the allele affinity for transcription factors.
The analysis of the study suggests that human epigenome in average covers approximately 200 adverse SD-ASM variants. The sensitivity of the genes with tissue-specific expression patterns gives the opportunity for the evolutionary innovation in gene regulation.
Haplotype reconstruction strategy is used to trace chromatin chemical modifications (using ChIP-seq) in a variety of human tissues. Haplotype-resolved epigenomic maps can trace allelic biases in chromatin configuration. A substantial variation among different tissues and individuals is observed. This allows the deeper understanding of cis-regulatory relationships between genes and control sequences.
Histone modification
Post-translational modifications of histone proteins, which include methylation, acetylation, phosphorylation, ubiquitination, and sumoylation. These modifications can either activate or repress gene expression by altering chromatin structure and accessibility of the DNA to transcriptional machinery.
The epigenetic profiles of human tissues reveals the following distinct histone modifications in different functional areas:
Acetylation
Histone acetylation neutralizes the positive charge on histones. This weakens the electrostatic attraction to negatively charged DNA and causes unwinding of DNA from histones, making the DNA more accessible to the transcriptional machinery and hence resulting in transcriptional activation.
Methylation
Can lead to activation or repression of gene expression depending on the specific amino acids that are methylated. | Epigenome | Wikipedia | 441 | 1506087 | https://en.wikipedia.org/wiki/Epigenome | Biology and health sciences | Genetics | Biology |
Non-coding RNA gene silencing
Non-coding RNA (ncRNA) gene silencing involves various types of non-coding RNAs, such as microRNAs (miRNAs), long non-coding RNAs (lncRNAs), and small interfering RNAs (siRNAs). These RNA molecules can modulate gene expression by various mechanisms, including mRNA degradation, inhibition of translation, and chromatin remodeling.
Structural modifications
During the last few years, several methods have been developed to study the structural and consequently the functional modifications of chromatin. The first project that used epigenomic profiling to identify regulatory elements in the human genome was ENCODE (Encyclopedia of DNA Elements) that focused on profiling histone modifications on cell lines. A few years later ENCODE was included in the International Human Epigenome Consortium (IHEC), which aims to coordinate international epigenome studies.
The structural modifications that these projects aim to study can be divided into five main groups:
Nucleosome occupancy to detect regions with regulatory genes;
Chromatin interactions and domains;
Topological associated domains (TADs)
Topological associated domains are a degree of structural organization of the genome of the cell. They are formed by regions of chromatin, sized from 100 kilobases up to megabases, which highly self-interact. The domains are linked by other genomic regions, which, based on their size, are either called “topological boundary regions” or “unorganized chromatin”. These boundary regions separate the topological domains from heterochromatin, and prevent the amplification of the latter. Topological domains are diffused in mammalian, although similar genome partitions were identified also in Drosophila.
Topological domains in humans, like in other mammalians, have many functions regarding gene expression and transcriptional control process. Inside these domains, the chromatin shows to be well tangled, while in the boundary regions chromatin interactions are far less present. These boundary areas in particular show some peculiarity that determine the functions of all the topological domains.
Firstly, they contain insulator regions and barrier elements, both of which function as inhibitors of further transcription from the RNA polymerase enzyme. Such elements are characterized by the massive presence of insulator binding proteins CTCF. | Epigenome | Wikipedia | 475 | 1506087 | https://en.wikipedia.org/wiki/Epigenome | Biology and health sciences | Genetics | Biology |
Secondly, boundary regions block heterochromatin spreading, thus preventing the loss of useful genetic informations. This information derives from the observation that the heterochromatin mark H3K9me3 sequences clearly interrupts near boundary sequences.
Thirdly, transcription start sites (TSS), housekeeping genes and tRNA genes are particularly abundant in boundary regions, denoting that those areas have a prolific transcriptional activity, thanks to their structural characteristics, different from other topological regions.
Finally, in the border areas of the topological domains and their surroundings there is an enrichment of Alu/B1 and B2 SINE retrotransposons. In the recent years, those sequences were referred to alter binding site of CTCF, thus interfering with expression of some genomic areas.
Further proofs towards a role in genetic modulation and transcription regulation refers to the great conservation of the boundary pattern across mammalian evolution, with a dynamic range of small diversities inside different cell types, suggesting that these topological domains take part in cell-type specific regulatory events.
Correlation between methylation and 3D structure
The 4D Nucleome project aims to realize a 3D maps of mammalian genomes in order to develop predictive models to correlate epigenomic modifications with genetic variation. In particular the goal is to link genetic and epigenomic modifications with the enhancers and promoters which they interact with in three-dimensional space, thus discovering gene-set interactomes and pathways as new candidates for functional analysis and therapeutic targeting.
Hi-C is an experimental method used to map the connections between DNA fragments in three-dimensional space on a genome-wide scale. This technique combines chemical crosslinking of chromatin with restriction enzyme digestion and next-generation DNA sequencing.
This kind of studies are currently limited by the lack or unavailability of raw data.
Clinical significance
Cancer
Epigenetics is a currently active topic in cancer research. Human tumors undergo a major disruption of DNA methylation and histone modification patterns. The aberrant epigenetic landscape of the cancer cell is characterized by a global genomic hypomethylation, CpG island promoter hypermethylation of tumor suppressor genes, an altered histone code for critical genes and a global loss of monoacetylated and trimethylated histone H4. | Epigenome | Wikipedia | 472 | 1506087 | https://en.wikipedia.org/wiki/Epigenome | Biology and health sciences | Genetics | Biology |
Aging
The idea that DNA damage drives aging by compromising transcription and DNA replication has been widely supported since it was initially developed the 1980s. In recent decades, evidence has accumulated supporting the additional idea that DNA damage and repair elicit widespread epigenome alterations that also contribute to aging (e.g.). Such epigenome changes include age-related changes in the patterns of DNA methylation and histone modification.
Research
As a prelude to a potential Human Epigenome Project, the Human Epigenome Pilot Project aims to identify and catalogue Methylation Variable Positions (MVPs) in the human genome. Advances in sequencing technology now allow for assaying genome-wide epigenomic states by multiple molecular methodologies. Micro- and nanoscale devices have been constructed or proposed to investigate the epigenome.
An international effort to assay reference epigenomes commenced in 2010 in the form of the International Human Epigenome Consortium (IHEC). IHEC members aim to generate at least 1,000 reference (baseline) human epigenomes from different types of normal and disease-related human cell types.
Roadmap epigenomics project
One goal of the NIH Roadmap Epigenomics Project is to generate human reference epigenomes from normal, healthy individuals across a large variety of cell lines, primary cells, and primary tissues. Data produced by the project, which can be browsed and downloaded from the Human Epigenome Atlas, fall into five types that assay different aspects of the epigenome and outcomes of epigenomic states (such as gene expression): | Epigenome | Wikipedia | 327 | 1506087 | https://en.wikipedia.org/wiki/Epigenome | Biology and health sciences | Genetics | Biology |
Histone Modifications – Chromatin Immunoprecipitation Sequencing (ChIP-Seq) identifies genome wide patterns of histone modifications using antibodies against the modifications.
DNA Methylation – Whole Genome Bisulfite-Seq, Reduced Representation Bisulfite-Seq (RRBS), Methylated DNA Immunoprecipitation Sequencing (MeDIP-Seq), and Methylation-sensitive Restriction Enzyme Sequencing (MRE-Seq) identify DNA methylation across portions of the genome at varying levels of resolution down to basepair level.
Chromatin Accessibility – DNase I hypersensitive sites Sequencing (DNase-Seq) uses the DNase I enzyme to find open or accessible regions in the genome.
Gene Expression – RNA-Seq and expression arrays identify expression levels or protein coding genes.
Small RNA Expression – smRNA-Seq identifies expression of small noncoding RNA, primarily miRNAs.
Reference epigenomes for healthy individuals will enable the second goal of the Roadmap Epigenomics Project, which is to examine epigenomic differences that occur in disease states such as Alzheimer's disease. | Epigenome | Wikipedia | 236 | 1506087 | https://en.wikipedia.org/wiki/Epigenome | Biology and health sciences | Genetics | Biology |
In geometry, a set of points in space are coplanar if there exists a geometric plane that contains them all. For example, three points are always coplanar, and if the points are distinct and non-collinear, the plane they determine is unique. However, a set of four or more distinct points will, in general, not lie in a single plane.
Two lines in three-dimensional space are coplanar if there is a plane that includes them both. This occurs if the lines are parallel, or if they intersect each other. Two lines that are not coplanar are called skew lines.
Distance geometry provides a solution technique for the problem of determining whether a set of points is coplanar, knowing only the distances between them.
Properties in three dimensions
In three-dimensional space, two linearly independent vectors with the same initial point determine a plane through that point. Their cross product is a normal vector to that plane, and any vector orthogonal to this cross product through the initial point will lie in the plane. This leads to the following coplanarity test using a scalar triple product:
Four distinct points, , are coplanar if and only if,
which is also equivalent to
If three vectors are coplanar, then if (i.e., and are orthogonal) then
where denotes the unit vector in the direction of . That is, the vector projections of on and on add to give the original .
Coplanarity of points in n dimensions whose coordinates are given
Since three or fewer points are always coplanar, the problem of determining when a set of points are coplanar is generally of interest only when there are at least four points involved. In the case that there are exactly four points, several ad hoc methods can be employed, but a general method that works for any number of points uses vector methods and the property that a plane is determined by two linearly independent vectors.
In an -dimensional space where , a set of points are coplanar if and only if the matrix of their relative differences, that is, the matrix whose columns (or rows) are the vectors is of rank 2 or less.
For example, given four points
if the matrix
is of rank 2 or less, the four points are coplanar.
In the special case of a plane that contains the origin, the property can be simplified in the following way:
A set of points and the origin are coplanar if and only if the matrix of the coordinates of the points is of rank 2 or less. | Coplanarity | Wikipedia | 512 | 1508434 | https://en.wikipedia.org/wiki/Coplanarity | Mathematics | Two-dimensional space | null |
Geometric shapes
A skew polygon is a polygon whose vertices are not coplanar. Such a polygon must have at least four vertices; there are no skew triangles.
A polyhedron that has positive volume has vertices that are not all coplanar. | Coplanarity | Wikipedia | 54 | 1508434 | https://en.wikipedia.org/wiki/Coplanarity | Mathematics | Two-dimensional space | null |
Magnetostatics is the study of magnetic fields in systems where the currents are steady (not changing with time). It is the magnetic analogue of electrostatics, where the charges are stationary. The magnetization need not be static; the equations of magnetostatics can be used to predict fast magnetic switching events that occur on time scales of nanoseconds or less. Magnetostatics is even a good approximation when the currents are not static – as long as the currents do not alternate rapidly. Magnetostatics is widely used in applications of micromagnetics such as models of magnetic storage devices as in computer memory.
Applications
Magnetostatics as a special case of Maxwell's equations
Starting from Maxwell's equations and assuming that charges are either fixed or move as a steady current , the equations separate into two equations for the electric field (see electrostatics) and two for the magnetic field. The fields are independent of time and each other. The magnetostatic equations, in both differential and integral forms, are shown in the table below.
Where ∇ with the dot denotes divergence, and B is the magnetic flux density, the first integral is over a surface with oriented surface element . Where ∇ with the cross denotes curl, J is the current density and is the magnetic field intensity, the second integral is a line integral around a closed loop with line element . The current going through the loop is .
The quality of this approximation may be guessed by comparing the above equations with the full version of Maxwell's equations and considering the importance of the terms that have been removed. Of particular significance is the comparison of the term against the term. If the term is substantially larger, then the smaller term may be ignored without significant loss of accuracy.
Re-introducing Faraday's law
A common technique is to solve a series of magnetostatic problems at incremental time steps and then use these solutions to approximate the term . Plugging this result into Faraday's Law finds a value for (which had previously been ignored). This method is not a true solution of Maxwell's equations but can provide a good approximation for slowly changing fields.
Solving for the magnetic field
Current sources
If all currents in a system are known (i.e., if a complete description of the current density is available) then the magnetic field can be determined, at a position r, from the currents by the Biot–Savart equation: | Magnetostatics | Wikipedia | 489 | 1509289 | https://en.wikipedia.org/wiki/Magnetostatics | Physical sciences | Magnetism | null |
This technique works well for problems where the medium is a vacuum or air or some similar material with a relative permeability of 1. This includes air-core inductors and air-core transformers. One advantage of this technique is that, if a coil has a complex geometry, it can be divided into sections and the integral evaluated for each section. Since this equation is primarily used to solve linear problems, the contributions can be added. For a very difficult geometry, numerical integration may be used.
For problems where the dominant magnetic material is a highly permeable magnetic core with relatively small air gaps, a magnetic circuit approach is useful. When the air gaps are large in comparison to the magnetic circuit length, fringing becomes significant and usually requires a finite element calculation. The finite element calculation uses a modified form of the magnetostatic equations above in order to calculate magnetic potential. The value of can be found from the magnetic potential.
The magnetic field can be derived from the vector potential. Since the divergence of the magnetic flux density is always zero,
and the relation of the vector potential to current is:
Magnetization
Strongly magnetic materials (i.e., ferromagnetic, ferrimagnetic or paramagnetic) have a magnetization that is primarily due to electron spin. In such materials the magnetization must be explicitly included using the relation
Except in the case of conductors, electric currents can be ignored. Then Ampère's law is simply
This has the general solution
where is a scalar potential. Substituting this in Gauss's law gives
Thus, the divergence of the magnetization, has a role analogous to the electric charge in electrostatics and is often referred to as an effective charge density .
The vector potential method can also be employed with an effective current density | Magnetostatics | Wikipedia | 364 | 1509289 | https://en.wikipedia.org/wiki/Magnetostatics | Physical sciences | Magnetism | null |
The black turtle bean is a small, shiny variety of the common bean (Phaseolus vulgaris) especially popular in Latin American cuisine, though it can also be found in the Cajun and Creole cuisines of south Louisiana. Like all varieties of the common bean, it is native to the Americas, but has been introduced around the world. It is also used in Indian cuisine, Tamil cuisine, where it is known as karuppu kaaramani and in Maharashtrian cuisine, where it is known as kala ghevada. It is widely used in Uttrakhand, where it is also known as "bhatt". It is a rich source of iron and protein. The black turtle bean is often simply called the black bean (, , , , , or in Spanish; and in Portuguese), although this terminology can cause confusion with at least three other types of black beans.
The black turtle bean is the only type of turtle bean. It is called turtle because of its hard outer "shell".
It is not to be confused with douchi, the Chinese dish made with black hulled soybeans.
Background
The black bean has a dense, meaty texture, which makes it popular in vegetarian dishes, such as frijoles negros and the Mexican-American black bean burrito. It is a very popular bean in various regions of Brazil, and is used in the national dish, feijoada. It is also a main ingredient of Moros y Cristianos in Cuba, is a required ingredient in the typical gallo pinto of Costa Rica and Nicaragua, is a fundamental part of Pabellón criollo in Venezuela, and is served in almost all of Latin America, as well as many Hispanic enclaves in the United States. In the Dominican Republic cuisine, it is also used for a variation of the Moros y Cristianos simply called Moro de habichuelas negras. The black turtle bean is also popular as a soup ingredient. In Cuba, black bean soup is a traditional dish, usually served with white rice. Black beans sticky rice is a Thai dessert.
The bean was first widely grown in the present-day United States after the Mexican–American War (1846–1848). However, initially the variety was primarily grown as a snap pea (for the edible seed pod). | Black turtle bean | Wikipedia | 477 | 1509614 | https://en.wikipedia.org/wiki/Black%20turtle%20bean | Biology and health sciences | Pulses | Plants |
It is also common to keep the boiled water of these beans (which acquires a black coloring) and consume it as a soup with other ingredients for seasoning (known as sopa negra, black soup, or as sopa de frijoles, bean soup), as a broth (caldo de frijol, bean broth) or to season or color other dishes (aforementioned gallo pinto, for example).
Samples of black turtle beans were reported in 2006 to contain total anthocyanins in their dried seed coats of 0−2.78 mg/g.
Gallery | Black turtle bean | Wikipedia | 121 | 1509614 | https://en.wikipedia.org/wiki/Black%20turtle%20bean | Biology and health sciences | Pulses | Plants |
A Bering Strait crossing is a hypothetical bridge or tunnel that would span the relatively narrow and shallow Bering Strait between the Chukotka Peninsula in Russia and the Seward Peninsula in the U.S. state of Alaska. The crossing would provide a connection linking the Americas and Afro-Eurasia.
With the two Diomede Islands between the peninsulas, the Bering Strait could be spanned by a bridge or tunnel.
There have been several proposals for a Bering Strait crossing made by various individuals and media outlets. The names used for them include "The Intercontinental Peace Bridge" and "EurasiaAmerica Transport Link". Tunnel names have included "TKMWorld Link", "AmerAsian Peace Tunnel" and InterBering. In April 2007, Russian government officials told the press that the Russian government would back a US$65 billion plan by a consortium of companies to build a Bering Strait tunnel.
History
19th century
The concept of an overland connection crossing the Bering Strait goes back before the 20th century. William Gilpin, first governor of the Colorado Territory, envisaged a vast "Cosmopolitan Railway" in 1890 linking the entire world through a series of railways.
Two years later, Joseph Strauss, who went on to design over 400 bridges, and then serve as the project engineer for the Golden Gate Bridge, put forward the first proposal for a Bering Strait rail bridge in his senior thesis. The project was presented to the government of the Russian Empire, but it was rejected.
20th century
In 1904, a syndicate of American railroad magnates proposed (through a French spokesman) a SiberianAlaskan railroad from Cape Prince of Wales in Alaska through a tunnel under the Bering Strait and across northeastern Siberia to Irkutsk via Cape Dezhnev, Verkhnekolymsk, and Yakutsk (around of railroad to build, plus over in North America). The proposal was for a 90-year lease, and exclusive mineral rights for each side of the right-of-way. It was debated by officials and finally turned down on March 20, 1907.
Czar Nicholas II approved the American proposal in 1905 (only as a permission, not much financing from the Czar). Its cost was estimated at $65 million and $300 million, including all the railroads. These hopes were dashed with the outbreak of the 1905 Russian Revolution followed by World War I. | Bering Strait crossing | Wikipedia | 482 | 1510249 | https://en.wikipedia.org/wiki/Bering%20Strait%20crossing | Technology | Multi-modal crossings | null |
A Nazi plan to create a wide-gauge railroad called the Breitspurbahn was mooted to connect the cities of Europe, India, China and ultimately North America via the Bering Strait. The railroad was never built.
Interest was renewed during World War II with the completion in 19421943 of the Alaska Highway, linking the remote territory of Alaska with Canada and the continental United States. In 1942, the Foreign Policy Association envisioned the highway continuing to link with Nome near the Bering Strait, linked by highway to the railhead at Yakutsk, using an alternative sea-and-air ferry service across the Bering Strait. At the same time the road on the Russian side was extended by building the Kolyma Highway.
In 1958, engineer Tung-Yen Lin suggested the construction of a bridge across the Bering Strait "to foster commerce and understanding between the people of the United States and the Soviet Union". Ten years later he organized the Inter-Continental Peace Bridge, Inc., a non-profit institution organized to further this proposal. At that time he made a feasibility study of a Bering Strait bridge and estimated the cost to be $1 billion for the span. In 1994 he updated the cost to more than $4 billion. Like Gilpin, Lin envisioned the project as a symbol of international cooperation and unity, and dubbed the project the Intercontinental Peace Bridge.
21st century
According to a report in the Beijing Times in May 2014, Chinese transport experts had proposed building a roughly high-speed rail line from northeast China to the United States. The project would include a tunnel under the Bering Strait and connect to the contiguous United States via Wales, Alaska, along the river to Fairbanks, Alaska, and along the Alaska Highway to Edmonton, Alberta, Canada. | Bering Strait crossing | Wikipedia | 357 | 1510249 | https://en.wikipedia.org/wiki/Bering%20Strait%20crossing | Technology | Multi-modal crossings | null |
Several American entrepreneurs have also advanced private-sector proposals, such as an Alaska-based limited-liability company InterBering founded in 2010 to lobby for a cross-straits connection, and a 2018 cryptocurrency offering to fund the construction of a tunnel. In 2005, investor Neil Bush, younger brother of U.S. President George W. Bush and son of President George H. W. Bush, traveled abroad with Sun Myung Moon of the Unification Church as he promoted a proposal to dig a transportation corridor beneath the Bering Strait. When questioned by Mother Jones during the Republican primary campaign of his brother Jeb Bush a decade later in 2015, he denied having supported the tunnel project and said that he had traveled with Moon because he supported "efforts by faith leaders to call their flock into service to others."
Strategic military concerns
Proposals to build a crossing predate the Russian invasion of Ukraine and the Russian-Ukrainian War, which started in February 2022. It is not known how those events have affected strategic concerns relating to the proposed crossing, which would facilitate access by Russia to North America. Even before the invasion, commentators on the proposed link have flagged strategic military concerns as a factor in any decision to build the crossing.
Technical concerns
Distance
The straight distance between Russia and Alaska is . If building bridges and using the Diomede Islands, the straight distance over water for the three parts would be , and , in total .
Depth of water
The depth of the water is a minor problem, as the strait is no deeper than , comparable to the English Channel. The tides and currents in the area are not severe.
Weather-related challenges
Restrictions on construction work
The route is just south of the Arctic Circle, and the location has long, dark winters and extreme weather, including average winter lows of and temperatures approaching in cold snaps. This would mean that construction work would likely be restricted to five months of the year, around May to September, and centered during summer.
Exposed steel
The weather also poses challenges to exposed steel. In Lin's design, concrete covers all structures, to simplify maintenance and to offer additional stiffening.
Ice floes
Although there are no icebergs in the Bering Strait, ice floes up to thick are in constant motion during certain seasons, which could produce forces on the order of on a pier.
Tundra in surrounding regions
Roads on either side of the strait would likely have to cross tundra, requiring either an unpaved road or some way to avoid the effects of permafrost. | Bering Strait crossing | Wikipedia | 511 | 1510249 | https://en.wikipedia.org/wiki/Bering%20Strait%20crossing | Technology | Multi-modal crossings | null |
Likely route and expenses
Bridge option
If the crossing is chosen as a bridge, it would probably connect Wales, Alaska, to a location south of Uelen. The bridge would also likely be divided by the Diomede Islands, which are at the middle of the Bering Strait.
In 1994, Lin estimated the cost of a bridge to be "a few billion" dollars. The roads and railways on each side were estimated to cost $50 billion. Lin contrasted this cost to petroleum resources "worth trillions". Discovery Channel's Extreme Engineering estimates the cost of a highway, electrified double-track high-speed rail, and pipelines at $105 billion (in 2007 US dollars), five times the original cost of the 1994 Channel Tunnel.
Connections to the rest of the world
This excludes the cost of new roads and railways to reach the bridge. Aside from the technical challenges of building two bridges or a more than tunnel across the strait, another major challenge is that, , there is nothing on either side of the Bering Strait to connect the bridge to.
Russian side
The Russian side of the strait, in particular, is severely lacking in infrastructure. No railways exist for over in any direction from the strait.
The nearest major connecting highway is the M56 Kolyma Highway, which is currently unpaved and around from the strait. However, by 2042, the Anadyr Highway is expected to be completed connecting Ola and Anadyr, which is only about from the strait.
U.S. side
On the U.S. side, an estimated of highways or railroads would have to be built around Norton Sound, through a pass along the Unalakleet River, and along the Yukon River to connect to Manley Hot Springs Road – in other words, a route similar to that of the Iditarod Trail Race. A project to connect Nome, from the strait, to the rest of Alaska by a paved highway (part of Alaska Route 2) has been proposed by the Alaskan state government, although the very high cost ($2.3 to $2.7 billion, about $3 million per kilometer, or $5 million per mile) has so far prevented construction.
In 2016, the Alaskan road network was extended westwards by to Tanana, from the strait, by building a fairly simple road. The Alaska Department of Transportation & Public Facilities project was supported by local indigenous groups such as the Tanana Tribal Council.
Track gauge | Bering Strait crossing | Wikipedia | 500 | 1510249 | https://en.wikipedia.org/wiki/Bering%20Strait%20crossing | Technology | Multi-modal crossings | null |
Another complicating factor is the different track gauges in use. Mainline rail in the US, Canada, China, and the Koreas uses standard gauge of 1435 millimeters. Russia uses the slightly broader Russian gauge of 1520 mm. Solutions to this break of gauge include:
To have all cargo in containers, which are fairly easily reloaded from one train to another. This is used on the increasingly popular China–Europe rail freight route, which has two breaks of gauge. It is possible to transfer a 60-container train in one hour.
Another solution is variable gauge axles for locomotives and rolling stock, such as those made by Talgo. A gauge changer modifies the gauge of the wheels while the train traverses the GC equipment at a speed of , which is about 4 seconds per railcar. This is faster than is possible with the transfer of ISO containers.
The TKMWorld Link
The TKMWorld Link (Russian: ТрансКонтинентальная магистраль, English: Transcontinental Railway), also called ICL-World Link (Intercontinental link), was a planned link between Siberia and Alaska to deliver oil, natural gas, electricity, and rail passengers to the United States from Russia. Proposed in 2007, the plan included provisions to build a tunnel under the Bering Strait, which, if built, would have been the longest tunnel in the world, surpassing the Line 3 (Guangzhou Metro) tunnel. The tunnel was intended to be part of a railway joining Yakutsk, the capital of the Russian republic of Yakutia, and Komsomolsk-on-Amur, in the Russian Far East, with the western coast of Alaska. The Bering Strait tunnel was estimated to cost between $10 billion and $12 billion, while the entire project was estimated to cost $65 billion.
In 2008, Russian Prime Minister Vladimir Putin approved the plan to build a railway to the Bering Strait area, as a part of the development plan to run until 2030. The more than tunnel would have run under the Bering Strait between Chukotka, in the Russian far east, and Alaska. The cost was estimated as $66 billion. | Bering Strait crossing | Wikipedia | 464 | 1510249 | https://en.wikipedia.org/wiki/Bering%20Strait%20crossing | Technology | Multi-modal crossings | null |
In late August 2011, at a conference in Yakutsk in eastern Russia, the plan was backed by some of President Dmitry Medvedev's top officials, including Aleksandr Levinthal, the deputy federal representative for the Russian Far East. Supporters of the idea believed that it would be a faster, safer, and cheaper way to move freight around the world than container ships. They estimated it could carry about 3% of global freight and make about $7 billion a year. Shortly after, the Russian government approved the construction of the $65 billion Siberia-Alaska rail and tunnel across the Bering Strait.
Observers doubted that the rail link would be cheaper than ship, bearing in mind that the cost for rail transport from China to Europe is higher than by ship (except for expensive cargo where lead time is important).
In 2013, the Amur Yakutsk Mainline connecting the Yakutsk railway ( from the strait) with the Trans-Siberian Railway was completed. However, this railway is meant for freight and is too tightly curved for high-speed passenger trains. Future projects include the and Kolyma–Anadyr highway. The Kolyma–Anadyr highway has started construction, but will be a narrow gravel road.
USCanadaRussiaChina railway
In 2014, China was considering construction of a US-Canada-Russia-China bullet train that would include a undersea tunnel crossing the Bering Strait and would allow passengers to travel between the United States and China in about two days.
Although the press was skeptical of the project, China's state-run China Daily claimed that China possessed the necessary technology. It was unknown who was expected to pay for the construction, although China had in other projects offered to build and finance them, and expected the money back in the end through fees or rents.
Trans-Eurasian Belt Development
In 2015, another possible collaboration between China and Russia was reported, part of the Trans-Eurasian Belt Development, a transportation corridor across Siberia that would also include a road bridge with gas and oil pipelines between the easternmost point of Siberia and the westernmost point of Alaska. It would link London and New York by rail and superhighway via Russia if it were to go ahead.
China's Belt and Road Initiative has similar plans, so the project would work in parallel for both countries. | Bering Strait crossing | Wikipedia | 471 | 1510249 | https://en.wikipedia.org/wiki/Bering%20Strait%20crossing | Technology | Multi-modal crossings | null |
Picea glauca (Moench) Voss., the white spruce, is a species of spruce native to the northern temperate and boreal forests in Canada and United States, North America.
Picea glauca is native from central Alaska all through the east, across western and southern/central Canada to the Avalon Peninsula in Newfoundland, Quebec, Ontario and south to Montana, North Dakota, Minnesota, Wisconsin, Michigan, Upstate New York and Vermont, along with the mountainous and immediate coastal portions of New Hampshire and Maine, where temperatures are just barely cool and moist enough to support it. There is also an isolated population in the Black Hills of South Dakota and Wyoming. It is also known as Canadian spruce, skunk spruce, cat spruce, Black Hills spruce, western white spruce, Alberta white spruce, and Porsild spruce.
Description
The white spruce is a large evergreen conifer which normally grows to tall, but can grow up to tall with a trunk diameter of up to . The bark is thin and scaly, flaking off in small circular plates across. The crown is narrowconical in young trees, becoming cylindrical in older trees. The shoots are pale buff-brown, glabrous in the east of the range, but often pubescent in the west, and with prominent pulvini. The leaves are needle-like, long, rhombic in cross-section, glaucous blue-green above (hence glauca) with several thin lines of stomata, and blue-white below with two broad bands of stomata.
The cones are pendulous, slender, cylindrical, long and 1.5 cm wide when closed, opening to 2.5 cm broad. They have thin, flexible scales 15 mm long with a smoothly rounded margin. They are green or reddish, maturing to pale brown 4 to 8 months after pollination. The seeds are black, 2 to 3 mm long, with a slender, tan wing 5 to 8 mm long.
Seeds
Seeds are small, 2.5 to 5 mm long, oblong, and acute at the base. Determinations of the average number of sound seeds per white spruce cone have ranged from 32 to 130.
Common causes of empty seed are lack of pollination, abortion of the ovule, and insect damage.
The average weight per individual seed varies from 1.1 mg to 3.2 mg. | Picea glauca | Wikipedia | 486 | 1511050 | https://en.wikipedia.org/wiki/Picea%20glauca | Biology and health sciences | Pinaceae | Plants |
Each seed is clasped by a thin wing 2 to 4 times as long as the seed. Seed and wing are appressed to the cone scale. Embryo and megagametophyte are soft and translucent at first; later the endosperm becomes firm and milky white, while the embryo becomes cream-coloured or light yellow. At maturity, the testa darkens rapidly from light brown to dark brown or black. Mature seeds "snaps in two" when cut by a sharp knife on a firm surface.
White spruce cones reach their maximum size after 800 GDD. Cone moisture content decreases gradually after about 1000 GDD.
Cone colour also can be used to help determine the degree of maturation, but cones may be red, pink or green. Collection and storage dates and conditions influence germination requirements and early seedling growth.
A bushel (35 L) of cones, which may contain 6,500 to 8,000 cones, yields of clean seed.
Seed dispersal begins after cone scales reflex with cone maturation in the late summer or early fall of the year of formation. Cones open at moisture contents of 45% to 70% and specific gravities of 0.6 to 0.8. Weather affects both the initiation and pattern of seed dispersal, but cone opening and the pattern of seed dispersal can vary among trees in the same stand. Even after dispersal has begun, cold, damp weather will cause cone scales to close; they will reopen during dry weather. Most seed falls early rather than late, but dispersal may continue through fall and winter and even into the next growing season. Seed dispersal occurs mainly in late summer or early fall.
White spruce seed is initially dispersed through the air by wind. Both the initiation and pattern of seed dispersal depend on the weather, but these can vary among trees in the same stand. Small amounts of white spruce seed are normally dispersed beyond 100 m from the seed source, but exceptionally seeds have been found more than 300–400 m from the nearest seed source.
Root system | Picea glauca | Wikipedia | 405 | 1511050 | https://en.wikipedia.org/wiki/Picea%20glauca | Biology and health sciences | Pinaceae | Plants |
The root system of white spruce is highly variable and adaptable, responding to a variety of edaphic factors, especially soil moisture, soil fertility, and mechanical impedance. On soils that limit rooting depth, the root system is plate-like, but it is a common misconception to assume that white spruce is genetically constrained to develop plate-like root systems irrespective of soil conditions. In the nursery, or naturally in the forest, white spruce usually develops several long 'running' roots just below the ground surface.
The structure of the tracheids in the long lateral roots of white spruce varies with soil nitrogen availability.
Stem
White spruce can live for several hundred years, with an estimated average lifespan of 250 to 300 years.
Slow-growing trees in rigorous climates are also capable of great longevity. White spruce high on the shore of Urquhart Lake, Northwest Territories, were found to be more than 300 years old.
Bark
The bark of mature white spruce is scaly or flaky, grey-brown or ash-brown, but silvery when freshly exposed. Resin blisters are normally lacking, but the Porsild spruce Picea glauca var. porsildii Raup has been credited with having smooth resin-blistered bark.
White spruce bark is mostly less than 8 mm and not more than 9.5 mm thick.
Chemistry
Isorhapontin can be found in spruce species such as the white spruce.
P. glauca has three different genomes; a nuclear genome, a mitochondrial genome, and a plastid (i.e. chloroplast) genome. The large (20 Gbp) nuclear genome of P. glauca (genotype WS77111) was published in 2015, and the organellar (plastid and mitochondrial) genomes (genotype PG29) were published in SD Jackman et al. 2015. The plastid genome of P. glauca (genotype WS77111) has also been published.
Varieties | Picea glauca | Wikipedia | 420 | 1511050 | https://en.wikipedia.org/wiki/Picea%20glauca | Biology and health sciences | Pinaceae | Plants |
Several geographical varieties have been described, but are not accepted as distinct by all authors. These comprise, from east to west:
Picea glauca var. glauca (typical or eastern white spruce): from Newfoundland west to eastern Alberta, on lowland plains.
Picea glauca var. densata (Black Hills white spruce): The Black Hills in South Dakota.
Picea glauca var. albertiana (Alberta white spruce): The Rocky Mountains in Alberta, British Columbia and northwest Montana.
Picea glauca var. porsildii (Alaska white spruce): Alaska and Yukon.
The two western varieties are distinguished by pubescent shoots, and may be related to extensive hybridisation and intergradation with the closely related Engelmann spruce found further south in the Rocky Mountains. White spruce also hybridises readily with the closely related Sitka spruce where they meet in southern Alaska and northwestern British Columbia; this hybrid is known as Picea × lutzii.
Distribution and habitat | Picea glauca | Wikipedia | 205 | 1511050 | https://en.wikipedia.org/wiki/Picea%20glauca | Biology and health sciences | Pinaceae | Plants |
White spruce has a transcontinental range in North America. In Canada, its contiguous distribution encompasses virtually the whole of the Boreal, Subalpine, Montane, Columbia, Great Lakes–St. Lawrence, and Acadian Forest Regions, extending into every province and territory. On the west coast of Hudson Bay, it extends to Seal River, about 59°N, "from which the northward limit runs apparently almost directly north-west to near the mouth of the Mackenzie River, or about latitude 68°". Collins and Sumner reported finding white spruce within 13 km of the Arctic coast in the Firth Valley, Yukon, at about 69°30′ N, 139°30′ W. It reaches within 100 km of the Pacific Ocean in the Skeena Valley, overlapping with the range of Sitka spruce (Picea sitchensis), and almost reaching the Arctic Ocean at latitude 69° N in the District of Mackenzie, with white spruce up to 15 m high occurring on some of the islands in the Delta near Inuvik. The wide variety of ecological conditions in which 4 Quebec conifers, including white spruce, are able to establish themselves, was noted by Lafond, but white spruce was more exacting than black spruce. In the United States, the range of white spruce extends into Maine, Vermont, New Hampshire, New York, Michigan, Wisconsin, Minnesota, and Alaska, where it reaches the Bering Strait in 66°44′ N" at Norton Bay and the Gulf of Alaska at Cook Inlet.
Southern outliers have been reported in southern Saskatchewan and the Cypress Hills of southwestern Saskatchewan and southeastern Alberta, northwestern Montana, south-central Montana, in the Black Hills on the Wyoming–South Dakota boundary, on the Manitoba–North Dakota boundary, and at Shushan, New York.
White spruce is the northernmost tree species in North America, reaching just north of 69°N latitude in the Mackenzie River delta. It grows between sea level and an elevation of . Its northern distribution roughly correlates to the location of the tree line, which includes an isothermic value of for mean temperature in July, as well as the position of the Arctic front; cumulative summer degree days, mean net radiation, and the amount of light intensities also figure. White spruce is generally found in regions where the growing season exceeds 60 days annually. | Picea glauca | Wikipedia | 477 | 1511050 | https://en.wikipedia.org/wiki/Picea%20glauca | Biology and health sciences | Pinaceae | Plants |
The southern edge of the zone in which white spruce forms 60% or more of the total stand corresponds more or less to the July isotherm of around the Great Lakes; in the Prairie Provinces its limit is north of this isotherm. During the summer solstice, day length values range from 17 hours at its southern limits to 24 hours above the Arctic Circle.
One of the hardiest conifers, white spruce in parts of its range withstands mean daily January temperature of and extreme minimum temperatures as low as ; minimum temperatures of are general throughout much of the range except the southernmost and southeasternmost parts. By itself, or with black spruce and tamarack (Larix laricina), white spruce forms the northern boundary of tree-form growth. White spruce up to 15 m in height occur at 69°N on islands in the Mackenzie Delta near Inuvik in the Northwest Territories. Hustich (1966) depicted Picea spp. as forming the northernmost limit of tree growth in North America.
The arctic or northern timberline in North America forms a broad transition zone from Labrador to northern Alaska. In Labrador, white spruce is not abundant and constitutes less than 5% of the forest, with a range that coincides very closely with that of black spruce but extending slightly further north. | Picea glauca | Wikipedia | 262 | 1511050 | https://en.wikipedia.org/wiki/Picea%20glauca | Biology and health sciences | Pinaceae | Plants |
The range of white spruce extends westwards from Newfoundland and Labrador, and along the northern limit of trees to Hudson Bay, Northwest Territories, Yukon, and into northwestern Alaska. Across western Canada and Alaska, white spruce occurs further north than black spruce, and, while poplar (Populus), willow, and birch may occur along streams well into the tundra beyond the limits of spruce, the hardwoods are usually no more than scrub. Spruce characteristically occurs in fingers of tree-form forest, extending far down the northern rivers and as scattered clumps of dwarfed "bush" spruce on intervening lands. In Manitoba, Scoggan noted that the northernmost collection of white spruce was at latitude 59°48’N, but Bryson et al. found white spruce in the northern edge of continuous forest in central Canada at Ennadai Lake, about 60°45′ N, 101°’W, just north of the northwest corner of Manitoba. Bryson et al. noted that the forest retained "the same general characteristics as when it was first described [by Tyrrell] in 1896". Collins and Sumner reported finding white spruce within 13 km of the Arctic coast in the Firth valley, Yukon, at about 69°30′ N, 139°30′ W, and Sargent noted that white spruce in Alaska "reached Behring Strait in 66°44′ N".
Climate, especially temperature, is obviously a factor in determining distributions of northern flora. Halliday and Brown suggested that white spruce's northern limit corresponds "very closely" with the July mean monthly isotherm of 10 °C in Ungava, but that the northern limit west of Hudson Bay was south of that isotherm. Other climatic factors that have been suggested as affecting the northern limit of white spruce include: cumulative summer degree days, position of the Arctic front in July, mean net radiation especially during the growing season, and low light intensities. Topography, soil conditions, and glaciation may also be important in controlling northern limits of spruce. | Picea glauca | Wikipedia | 410 | 1511050 | https://en.wikipedia.org/wiki/Picea%20glauca | Biology and health sciences | Pinaceae | Plants |
The southern limit of distribution of white spruce is more complex. From east of the main range of coastal mountains in British Columbia, the southern continuous limit of white spruce is the forest/prairie interface through Alberta, Saskatchewan, Manitoba, the northern parts of Minnesota and Wisconsin, central Michigan, northeastern New York, and Maine. Sargent and Harlow and Harrar also included Vermont and New Hampshire; and, while Dame and Brooks excluded New York and states further west, they included Massachusetts as far south as Amherst and Northampton, "probably the southern limit of the species" in that area. Nisbet gave the range of white spruce as extending to "Carolina", but he did not recognize red spruce as a species and presumably included it with white spruce.
Towards the southern parts of its range, white spruce encounters increasingly effective ecological competition from hardwoods, some of which may reinforce their growth-rate or sprouting competitiveness with allelopathic depredation of coniferous regeneration. Further southward extension of the distribution is inhibited by white spruce's cold requirement.
As an exotic species
As an exotic, white spruce is widespread but uncommon. It was introduced into England and parts of continental Europe in or soon after the year 1700, into Denmark about 1790, and into Tasmania and Ceylon shortly before 1932.
Nisbet noted that firmly-rooted white spruce served very well to stabilize windswept edges of woods in Germany. In a narrow belt of mixed Norway and white spruces over an extremely exposed hilltop crest at high elevation in northern England, the Norway spruce were "completely dwarfed" whereas the white spruce had reached heights of between 3 and 4.3 m. The age of the belt was not recorded, but adjoining 66-year-old stands may have been of the same vintage.
White spruce has also been used as a minor plantation species in England and Scotland. In Scotland, at Corrour, Inverness-shire, Sir John Stirling Maxwell in 1907 began using white spruce in his pioneering plantations at high elevations on deep peat. However, plantations in Britain have generally been unsatisfactory, mainly because of damage by spring frosts after mild weather had induced flushing earlier in the season. However, the species is held in high regard in the Belgian peat region, where it grows better than other spruces.
Ecology | Picea glauca | Wikipedia | 463 | 1511050 | https://en.wikipedia.org/wiki/Picea%20glauca | Biology and health sciences | Pinaceae | Plants |
White spruce is a climax canopy tree in the boreal forests of Canada and Alaska. It generally occurs on well-drained soils in alluvial and riparian zones, although it also occurs in soils of glacial and lacustrine origin. The understory is dominated by feather mosses (Hylocomium splendens, Pleurozium schreberi, Ptilium crista-castrensis) and fork mosses, and occasionally peat moss. In the far north, the total depth of the moss and underlying humus is normally between , although it tends to be shallower when hardwoods are present in the stand.
White spruce grows in soils with pH values of 4.7–7.0, although they have been found in soils as acidic as 4.0 in subalpine fir forests in the Northwest Territories. A presence of calcium in the soil is common to white spruce found in northern New York. White spruce most commonly grows in the soil orders of Alfisols and Inceptisols. Soil properties such as fertility, temperature, and structural stability are partial determinants of the ability of white spruce to grow in the extreme northern latitudes. In the northern limits of its range, white spruce is the climax species along with black spruce; birch and aspen are the early succession species.
Wildfires typically occur every 60 to 200 years, although they have been known to occur as infrequently as every 300 years.
White spruce will grow in USDA Growing Zones 3–7, but is not adapted to heat and humidity and will perform poorly in a hot climate. The tree attains its greatest longevity and growth potential in Zones 3–4.
Wildlife such as deer, rabbits, and grouse browse the foliage during the winter. The seeds are eaten by small mammals like the red squirrel and birds such as chickadee, nuthatch, and pine siskin.
Soils | Picea glauca | Wikipedia | 390 | 1511050 | https://en.wikipedia.org/wiki/Picea%20glauca | Biology and health sciences | Pinaceae | Plants |
White spruce occurs on a wide variety of soils, including soils of glacial, lacustrine, marine, and alluvial origins; overlying basic dolomites, limestones and acidic Precambrian and Devonian granites and gneisses; and Silurian sedimentary schists, shales, slates, and conglomerates. The wide range of textures accommodated includes clays, even those that are massive when wet and columnar when dry, sand flats, and coarse soils. Its occurrence on some organic soils is not characteristic, except perhaps on shallow mesic organic soils in Saskatchewan and in association with black spruce on organic soils in central Yukon.
Podzolized, brunisolic, luvisolic, gleysolic, and regosolic (immature) soils are typical of those supporting white spruce throughout the range of the species. Soils supporting white spruce are most commonly Alfisols or Inceptisols. In the podzol region of Wisconsin, white spruce occurs on loam podzols, podzolized gley loams, strongly podzolized clays, gley-podzol clays, stream-bottom soils, and wood peat. Moist sandy loams also support good growth. On sandy podzols, it is usually a minor species. Good development occurs on moist alluvium on the banks of streams and borders of swamps. White spruce makes good growth on well-drained lacustrine soils in Alberta Mixedwoods, on moderately-well-drained clay loams in Saskatchewan,, and on melanized loams and clays (with sparse litter and a dark-coloured organically-enriched mineral horizon) in the Algoma district of Ontario.
White spruce becomes less accommodating of soil with increasing severity of climate. The distribution of white spruce in Labrador seems to depend almost entirely on the character of the soil, and between the southwestern shores of Hudson Bay and the northeastern regions of Saskatchewan, white spruce is confined to very local physiographic features, characterized by well-drained or fertile soils. | Picea glauca | Wikipedia | 422 | 1511050 | https://en.wikipedia.org/wiki/Picea%20glauca | Biology and health sciences | Pinaceae | Plants |
On dry, deep, outwash deposits in northern Ontario, both white spruce and aspen grow slowly. But, broadly, white spruce is able to tolerate considerable droughtiness of sites that are fertile, and no fertile site is too moist unless soil moisture is stagnant. Soil fertility holds the key not just to white spruce growth but to the distribution of the species. At least moderate fertility is needed for good growth, but white spruce occurs on many sites where nutrient deficiencies depress its growth more than that of black spruce, red spruce, Norway spruce, and the pines generally. Minimum soil-fertility standards recommended for white spruce sufficient to produce 126 to 157 m3/ha of wood at 40 years are much higher than for pine species commonly planted in the Lake States (Wilde 1966): 3.5% organic matter, 12.0 meq/100 g exchange capacity, 0.12% total N, 44.8 kg/ha available P, 145.7 kg/ha available K, 3.00 meq/100 g exchangeable Ca, and 0.70 meq/100 g exchangeable Mg.
Forest floors under stands dominated by white spruce respond in ways that vary with site conditions, including the disturbance history of the site. Composition, biomass, and mineral soil physical and chemical properties are affected. In Alaska, the accumulation of organic layers (to greater thicknesses in mature stands of spruce than those in hardwood stands on similar sites) leads to decreased soil temperatures, in some cases leading to the development of permafrost. Acidity of the mineral soil sampled at an average depth of 17 cm in 13 white spruce stands on abandoned farmland in Ontario increased by 1.2 pH units over a period of 46 years. | Picea glauca | Wikipedia | 348 | 1511050 | https://en.wikipedia.org/wiki/Picea%20glauca | Biology and health sciences | Pinaceae | Plants |
A considerable range of soil pH is tolerated by white spruce. Thrifty stands of white spruce in Manitoba have developed on soils of pH 7.6 at only 10 cm below the surface, and pH 8.4 at 43 cm below the surface; rooting depth in those soils was at least 81 cm. An abundant calcium supply is common to most white spruce locations in New York state. Chlorosis was observed in young white spruce in heavily limed nursery soils at about pH 8.3. Wilde gave 4.7 to 6.5 as the approximate optimum range of pH for white spruce in Wisconsin, but optimum growth seems possible at pH levels up to 7.0 and perhaps higher. Alluvium on the floodplains of northern rivers shows pH levels from 5.0 to 8.2. High-lime ecotypes may exist, and in Canada Forest Section B8 the presence of balsam poplar and white spruce on some of the moulded moraines and clays seems to be correlated with the considerable lime content of these materials, while calcareous soils are favourable sites for northern outliers of white spruce.
Mature stands of white spruce in boreal regions often have well-developed moss layers dominated by feather mosses, e.g., Hylocomium splendens, Pleurozium schreberi, Ptlium crista-castrensis, and Dicranum, rather than Sphagnum. The thickness of the moss–organic layer commonly exceeds 25 cm in the far north and may approach twice that figure. The mosses compete for nutrients and have a major influence on soil temperatures in the rooting zone. Permafrost development in parts of Alaska, Yukon, and the Northwest Territories is facilitated by the insulative organic layer (Viereck 1970a, b, Gill 1975, Van Cleve and Yarie 1986).
Cold hardiness
White spruce is extremely hardy to low temperatures, provided the plant is in a state of winter dormancy. Throughout the greater part of its range, white spruce routinely survives and is undamaged by winter temperatures of , and even lower temperatures occur in parts of the range. Boreal Picea are among the few extremely hardy conifers in which the bud primordia are able to survive temperatures down to . | Picea glauca | Wikipedia | 474 | 1511050 | https://en.wikipedia.org/wiki/Picea%20glauca | Biology and health sciences | Pinaceae | Plants |
Especially important in determining the response of white spruce to low temperatures is the physiological state of the various tissues, notably the degree of "hardening" or dormancy. A natural progression of hardening and dehardening occurs in concert with the seasons. While different tissues vary in ability to tolerate exposure to stressful temperatures, white spruce, as with woody plants in general, has necessarily developed sufficient winter hardiness in its various tissues to enable them to survive the minimum temperatures experienced in the distribution range.
White spruce is subject to severe damage from spring frosts. Newly flushed shoots of white spruce are very sensitive to spring frost. This sensitivity is a major constraint affecting young trees planted without overstorey nurses in boreal climates.
Forest succession
Forest succession in its traditional sense implies two important features that resist direct examination. First, classical definitions generally connote directional changes in species composition and community structure through time, yet the time frame needed for documentation of change far exceeds an average human lifespan. The second feature that defies quantitative description is the end point or climax.
Floodplain deposits in the Northwest Territory, Canada, are important in relation to the development of productive forest types with a component of white spruce. The most recently exposed surfaces are occupied by sandbar vegetation or riparian shrub willows and Alnus incana. With increasing elevation, the shrubs give way successively to balsam poplar and white spruce forest. In contrast, older floodplains, with predominantly brown wooded soils, typically carry white spruce–trembling aspen mixedwood forest.
Interrelationships among nutrient cycling, regeneration, and subsequent forest development on floodplains in interior Alaska were addressed by Van Cleve et al., who pointed out that the various stages in primary succession reflect physical, chemical, and biological controls of ecosystem structure and function. Thus, each successional stage has a species combination in harmony with site quality. Short-circuiting succession by planting a late successional species such as white spruce on an early successional surface may result in markedly reduced growth rates because of nitrogen insufficiency. Without application of substantial amounts of fertilizer, use would have to be made of early successional alder and its site-ameliorating additions of nitrogen. | Picea glauca | Wikipedia | 448 | 1511050 | https://en.wikipedia.org/wiki/Picea%20glauca | Biology and health sciences | Pinaceae | Plants |
Neiland and Viereck noted that “the slow establishment and growth of spruce under birch stands [in Alaska] may be partially due to effects of shading and general competition for water and nutrients, but may also be more directly related to the birch itself. Heikinheimo found that birch ash inhibited white spruce seedlings, and Gregory found that birch litter has a smothering effect on spruce seedlings.".
On dry upland sites, especially south-facing slopes, the mature vegetation is white spruce, white birch, trembling aspen, or a combination of these species. Succession follows in one of two general patterns. In most cases, aspen and birch develop as a successional stage after fire before reaching the spruce stage. But, occasionally, with optimal site conditions and a source of seed, white spruce will invade with the hardwoods or within a few years thereafter, thereby producing even-aged white spruce stands without an intervening hardwood stage.
Associated forest cover | Picea glauca | Wikipedia | 194 | 1511050 | https://en.wikipedia.org/wiki/Picea%20glauca | Biology and health sciences | Pinaceae | Plants |
The White Spruce Cover Type may include other species in small numbers. In Alaska, associates include paper birch, trembling aspen, balsam poplar, and black spruce; in western Canada, additional associates are subalpine fir, balsam fir, Douglas-fir, jack pine, and lodgepole pine. Seral species giving way to white spruce include paper birch, aspen, balsam poplar, jack pine, and lodgepole pine. On certain river bottom sites, however, black spruce may replace white spruce. Earlier successional stages leading to the white spruce climax are the white spruce–paper birch, white spruce–aspen, balsam poplar, jack pine, and lodgepole pine types. The type shows little variation. The forest is generally closed and the trees well formed, other than those close to the timberline. Lesser vegetation in mature stands is dominated by mosses. Vascular plants are typically few, but shrubs and herbs that occur “with a degree of regularity” include: alder, willows, mountain cranberry, red-fruit bearberry, black crowberry, prickly rose, currant, buffaloberry, blueberry species, bunchberry, twinflower, tall lungwort, northern comandra, horsetail, bluejoint grass, sedge species, as well as ground-dwelling mosses and lichens. Several white spruce communities have been identified in interior Alaska: white spruce/feathermoss; white spruce/dwarf birch/feathermoss; white spruce/dwarf birch/sphagnum; white spruce/avens/moss; and white spruce/alder/bluejoint.
Of the Eastern Forest Cover Types recognized by the Society of American Foresters, only one, White Spruce, names that species in its title. The eastern White Spruce Cover Type, as defined, encompasses white spruce both in pure stands, and in mixed stands "in which white spruce is the major [undefined] component."
In most of its range, white spruce occurs more typically in association with trees of other species than in pure stands. | Picea glauca | Wikipedia | 420 | 1511050 | https://en.wikipedia.org/wiki/Picea%20glauca | Biology and health sciences | Pinaceae | Plants |
White spruce is an associated species in the following Eastern Forest cover types, by the Society of American Foresters; in the Boreal Forest Region: (1) jack pine, (5) balsam fir, (12) black spruce, (16) aspen, (18) paper birch, and (38) tamarack; in the Northern Forest Region: (15) red pine, (21) eastern white pine, (24) hemlock-yellow birch, (25) sugar maple-beech-yellow birch, (27) sugar maple, (30) red spruce-yellow birch, (32) red spruce, (33) red spruce-balsam fir, (37) northern white-cedar, and (39) black ash-American elm-red maple.
Predators
Outbreaks of spruce beetles have destroyed over of forests in Alaska.
Although sometimes described as relatively resistant to attack by insects and disease, white spruce is far from immune to depredation. Important insect pests of white spruce include the spruce budworm (Choristoneura fumiferana), the yellow-headed spruce sawfly (Pikonema alaskensis), the European spruce sawfly (Gilpinia hercyniae), the spruce bud moth (Zeiraphera canadensis), and spruce beetle (Dendroctonus rufipennis). As well, other budworms, sawflies, and bark beetles, gall formers, bud midges, leaf miners, aphids, leaf eaters, leaf rollers, loopers, mites, scales, weevils, borers, pitch moths, and spittlebugs cause varying degrees of damage to white spruce.
A number of sawflies feed on spruce trees. Among them European spruce sawfly, yellow-headed spruce sawfly, green-headed spruce sawfly and the spruce webspinning sawfly.
More than a dozen kinds of looper feed on the spruces, fir, and hemlock in eastern Canada. The full-grown larvae of the larvae vary in length from 15 mm to 35 mm. Some feed briefly in the fall and complete their feeding in the spring; others feed mainly in the summer; still others feed mainly in the late summer and fall. | Picea glauca | Wikipedia | 460 | 1511050 | https://en.wikipedia.org/wiki/Picea%20glauca | Biology and health sciences | Pinaceae | Plants |
The fall and spring feeding group includes the dash-lined looper (Protoboarmia porcelaria indicataria), the diamond-backed looper (Hypagyrtis piniata), the fringed looper (Campaea perlata), and the false loopers (Syngrapha species). The summer feeding group includes the false hemlock looper (Nepytia canosaria Walker), occasionally occurring in large numbers and usually in conjunction with the hemlock looper (Lambdina fiscellaria), the Eupithecia species, the yellowlined conifer looper (Cladara limitaria), and the saddleback looper (Ectropis crepuscularia).
The late summer and fall group includes the common spruce-fir looper (Semiothisa signaria dispuncta) and the similar hemlock angle (moth) Macaria fissinotata on hemlock, the small spruce loopers Eupithecia species, the gray spruce looper Caripeta divisata, occasionally abundant, the black-dashed hydriomena moth (Hydriomena divisaria), and the whitelined looper (Eufidonia notataria).
Cultivars
Numerous cultivars of various sizes, colours and shapes have been selected for use in parks and gardens. The following have gained the Royal Horticultural Society's Award of Garden Merit.
Picea glauca 'Echiniformis'
Picea glauca var. albertiana 'Alberta Globe'
Picea glauca var. albertiana 'Conica'
'Conica' is a dwarf conifer with very slender leaves, like those normally found only on one-year-old seedlings, and very slow growth, typically only per year. Older specimens commonly 'revert', developing normal adult foliage and starting to grow much faster; this 'reverted' growth must be pruned if the plant is to be kept dwarf.
Uses
The wood of white spruce is of a lower quality than that of Engelmann spruce, but is stronger. It was used to make shelters and as firewood by Native Americans and European settlers in Alaska, where lodgepole pine does not grow. The wood is of major economic importance in Canada, being harvested for paper and construction. It is also used as a Christmas tree. | Picea glauca | Wikipedia | 487 | 1511050 | https://en.wikipedia.org/wiki/Picea%20glauca | Biology and health sciences | Pinaceae | Plants |
The wood is also exported to Japan where, known as "shin-kaya", it is used to make go boards as a substitute for the rare kaya wood. Additionally, Picea glauca var. densata is used for bonsai.
White spruce is the provincial tree of Manitoba and the state tree of South Dakota.
The new growth or tips of white spruce is used in beer making, gin production, flavouring soda, candy making or in pickles and preserves. | Picea glauca | Wikipedia | 99 | 1511050 | https://en.wikipedia.org/wiki/Picea%20glauca | Biology and health sciences | Pinaceae | Plants |
Picea engelmannii, with the common names Engelmann spruce, white spruce, mountain spruce, and silver spruce, is a species of spruce native to western North America. Highly prized for producing distinctive tone wood for acoustic guitars and other instruments, it is mostly a high-elevation mountain tree but also appears in watered canyons.
Description
Picea engelmannii is a medium-sized to large evergreen tree growing to tall, exceptionally to tall, and with a trunk diameter of up to . The reddish bark is thin and scaly, flaking off in small circular plates across. The crown is narrow conic in young trees, becoming cylindric in older trees. The shoots are buff-brown to orange-brown, usually densely pubescent, and with prominent pulvini. The leaves are needle-like, long, flexible, rhombic in cross-section, glaucous blue-green above with several thin lines of stomata, and blue-white below with two broad bands of stomata. The needles have a pungent odour when crushed.
Purple cones of about appear in spring, releasing yellow pollen when windy. The cones are pendulous, slender cylindrical, long and broad when closed, opening to broad. They have thin, flexible scales long, with a wavy margin. They are reddish to dark purple, maturing to light brown 4–7 months after pollination. The seeds are black, long, with a slender, long light brown wing.
The tree grows in a krummholz form along the fringe of alpine tundras.
Distribution
Engelmann spruce is mostly a higher-elevation mountain tree, in many areas reaching the tree line, but at lower elevations occupies cool watered canyons. It grows from above sea level, rarely lower towards the northwest.
Englemann spruce is native to western North America, common in the Rocky Mountains and east slopes of the Cascade Range from central British Columbia to Southern Oregon in the Cascades and Montana, Idaho, and Colorado, and more sparsely towards Arizona and New Mexico in the Sky islands; there are also two isolated populations in Northern Mexico. | Picea engelmannii | Wikipedia | 435 | 1511315 | https://en.wikipedia.org/wiki/Picea%20engelmannii | Biology and health sciences | Pinaceae | Plants |
It appears in the canyons of the Idaho Panhandle and more limitedly in the northeastern Olympic Mountains, which features some exceptionally large specimens, including one in diameter and tall. It can be found in the Cascade Range, mostly on the eastern slopes, from elevations of and liberally in the Rocky Mountains. It can also be found in the Monashee and Selkirk Mountains, as well as the highlands surrounding the Interior Plateau.
Ecology
Because transpiration is greatly reduced in small saplings while engulfed in snowpack, increased rates of transpiration in response to loss of snowpack, coupled with low sapwood water reserves and an extended period of soil frost in windswept areas, may prevent Engelmann spruce from regenerating in open areas both above and below the tree line. Both water uptake and water stored in roots appear to be critical for the survival of subalpine Engelmann spruce saplings that are exposed above the snowpack in later winter to early spring.
For exposed trees, the availability of soil water may be critical in late winter, when transpirational demands increase. Cuticular damage by windblown ice is probably more important at the tree line, but damage caused by desiccation is likely to be more important at lower elevations.
Despite wind damage, the species tends to grow taller than others at the tree line. It is shade tolerant, but not so much as subalpine fir, rendering it somewhat dependent on fires to outgrow competitors, although its thin bark and shallow roots make it vulnerable to fire. Spruce bark beetles attack the tree, being particularly deadly to groups which have stood for centuries. It is also susceptible to avalanches.
Although older spruce forests are not very useful to animals for forage, they can become so after fires, as they often burn completely, allowing many other plants, especially deciduous, to rise. Engelmann spruce-shaded streams are exploited by trout, and aphids produce galls which hang from the tree and look similar to cones when they dry out.
Subspecies and hybrids | Picea engelmannii | Wikipedia | 413 | 1511315 | https://en.wikipedia.org/wiki/Picea%20engelmannii | Biology and health sciences | Pinaceae | Plants |
Two geographical subspecies (treated as varieties by some authors, and as distinct species by others) occur:
Picea engelmannii subsp. engelmannii (Engelmann spruce). All of the range except as below.
Picea engelmannii subsp. mexicana (Mexican spruce). Two isolated populations on high mountains in northern Mexico, on the Sierra del Carmen in Coahuila (Sierra Madre Oriental) and on Cerro Mohinora in Chihuahua (Sierra Madre Occidental). Engelmann spruces of the Madrean sky islands mountains in the extreme southeast of Arizona and southwest of New Mexico also probably belong to this subspecies, though this is disputed.
The Engelmann spruce hybridises and intergrades extensively with the closely related white spruce (Picea glauca), found further north and east in the Rockies, and to a lesser extent with the closely related Sitka spruce where they meet on the western fringes of the Cascades.
Uses
Native Americans made various medicines from the resin and foliage.
Engelmann spruce is of economic importance for its wood, being light and fairly strong. It is harvested for paper-making and general construction. Wood from slow-grown trees at high elevation is especially prized for making soundboards for musical instruments such as acoustic guitars, harps, violins, and pianos.
Because it is odourless and has little resin, it has been used for food containers such as barrels. It is also used to a small extent as a Christmas tree.
Gallery | Picea engelmannii | Wikipedia | 311 | 1511315 | https://en.wikipedia.org/wiki/Picea%20engelmannii | Biology and health sciences | Pinaceae | Plants |
Astrapotheria is an extinct order of South American and Antarctic hoofed mammals that existed from the late Paleocene to the Middle Miocene, . Astrapotheres were large, rhinoceros-like animals and have been called one of the most bizarre orders of mammals with an enigmatic evolutionary history.
The taxonomy of this order is not clear, but it may belong to Meridiungulata (along with Notoungulata, Litopterna, Pyrotheria and Xenungulata). In turn, Meridungulata is believed to belong to the extant superorder Laurasiatheria. Some scientists have regarded the astrapotheres (and sometimes the Meridiungulata as a whole) as members of the clade Atlantogenata. However, collagen and mitochondrial DNA sequence data analysed in 2015 places at least the notoungulates and litopterns firmly within Laurasiatheria, as a sister group to the perissodactyls.
Description
Their lophodont molars and tusk-like canines became extremely large and ever-growing in later astrapotheres. The upper molars lack an ectocingulum and are dominated by well-developed ectoloph and protoloph. Additional lophs formed in some derived taxa. They had lower molars with two cross-lophs, including a high protocristid, and eventually became almost selenodont. As a result, their dentition is similar to notoungulates, but it seems to have evolved independently. The cheek teeth are similar to rhinocerotoids, including similar microstructure, which indicate they had the same function.
Postcranially, astrapotheres are relatively robust and more or less graviportal but have slender long bones, most notably in the hindlegs, suggesting they were amphibious. In order to support their proboscises and large heads they had relatively long and massive necks in relation to the rest of the vertebral column. Their feet are pentadactyl with short and stout podial and metapodial bones. Most characteristic for the order are the flat astragalus, equipped with a short neck and a flat head, articulating with both the navicular and cuboid bones; and their calcaneus with its enlarged peroneal tubercle. | Astrapotheria | Wikipedia | 494 | 14411152 | https://en.wikipedia.org/wiki/Astrapotheria | Biology and health sciences | Mammals: General | Animals |
Three families are recognized: Eoastrapostylopidae from the late Paleocene, Trigonostylopidae from the Paleocene-Eocene, and Astrapotheriidae from the Eocene-Miocene. The Brazilian, Itaboraian Tetragonostylops and the Argentinian, Riochican Eoastrapostylops are the oldest astrapotheres. The latter, with its low-crowned and lophoselenodont cheek teeth, is considered the most primitive astrapothere. Trigonostylopids are distinct from other astrapotheres in their ear anatomy but are included in the order because of otherwise similar characters. Antarctodon is one of few eutherian mammals, as well as one of the last known terrestrial vertebrates, found in Antarctica.
The most famous member of the order is undoubtedly Astrapotherium, a long elephant-like animal that had lost its upper incisors and developed ever-growing canine tusks. They had lost their anterior premolars, resulting in a gap between their tusks and the hypsodont cheek teeth. The short and retracted nasal bones indicate a moderately developed tapir-like proboscis. The small Eocene Trigonostylops lacked such retracted nasals and probably also a proboscis. Other astrapotheriids, such as the Casamayoran Scaglia and Albertogaudrya, were between a sheep and a tapir in size and already the largest South American mammals.
Classification
There is no scientific consensus regarding the classification within Astrapotheria. For example, originally described Tetragonostylops as a trigonostylopid but Soria 1982 and 1984 transferred the genus to Astrapotheriidae and concluded that the remaining two genera in that family, Trigonostylops and Shecenia, form a basal collateral branch within Astrapotheriidae. According to , Trigonostylopidae (including Eoastrapostylopidae) is the stem group of Astrapotheriidae. | Astrapotheria | Wikipedia | 432 | 14411152 | https://en.wikipedia.org/wiki/Astrapotheria | Biology and health sciences | Mammals: General | Animals |
Astrapotheriidae
Albertogaudrya
Antarctodon
Astraponotus
Astrapothericulus
Astrapotherium
Comahuetherium
Granastrapotherium
Hilarcotherium
Liarthrus
Maddenia
Parastrapotherium
Scaglia
Uruguaytherium
Xenastrapotherium
Eoastrapostylopidae
Eoastrapostylops
Trigonostylopidae
Shecenia
Tetragonostylops
Trigonostylops | Astrapotheria | Wikipedia | 99 | 14411152 | https://en.wikipedia.org/wiki/Astrapotheria | Biology and health sciences | Mammals: General | Animals |
Eczema herpeticum is a rare but severe and contagious disseminated infection that generally occurs at sites of skin damage produced by, for example, atopic dermatitis, burns, long-term usage of topical steroids or eczema. It is also known as Kaposi varicelliform eruption, Pustulosis varioliformis acute and Kaposi–Juliusberg dermatitis.
Some sources reserve the term "eczema herpeticum" when the cause is due to human herpes simplex virus, and the term "Kaposi varicelliform eruption" to describe the general presentation without specifying the virus.
This condition is most commonly caused by herpes simplex virus type 1 or 2, but may also be caused by coxsackievirus A16, or vaccinia virus. It appears as numerous umbilicated vesicles superimposed on healing atopic dermatitis. it is often accompanied by fever and lymphadenopathy. Eczema herpeticum can be life-threatening in babies.
Presentation
In addition to the skin, this infection affects multiple organs, including the eyes, brain, lung, and liver, and can be fatal.
Treatment
It can be treated with systemic antiviral drugs, such as aciclovir or valganciclovir. Foscarnet may also be used for immunocompromised host with Herpes simplex and acyclovir-resistant Herpes simplex.
Epidemiology
Even though the disease may develop at any age it is mostly present in childhood. Those who are affected typically have pre-existing cutaneous condition like atopic dermatitis.
History
Eczema herpeticum was first described by Hungarian dermatologist Moriz Kaposi in 1887. Fritz Juliusberg coined the term Pustulosis varioliformis acute in 1898. Eczema herpeticum is caused by Herpes simplex virus HSV1, the virus that causes cold sores; it can also be caused by other related viruses. | Eczema herpeticum | Wikipedia | 427 | 4086303 | https://en.wikipedia.org/wiki/Eczema%20herpeticum | Biology and health sciences | Viral diseases | Health |
Strix is a genus of owls in the typical owl family (Strigidae), one of the two generally accepted living families of owls, with the other being Tytonidae. Common names are earless owls or wood owls, though they are not the only owls without ear tufts, and "wood owl" is also used as a more generic name for forest-dwelling owls.
These are medium-sized to large, robustly built, powerful owls. They do not have ear tufts and most are highly nocturnal woodland birds. Most prey on small mammals, birds, and reptiles.
Most owls in the genus Strix can be distinguished from other genera of owls through their hooting vocalization and lack of visible ears.
The Latin genus name Strix referred to a mythical vampiric owl-monster believed to suck the blood of infants. Although the genus Strix was established for the earless owls by Linnaeus in 1758, many applied the term to other owls (namely the Tyto) until the late 19th century. This genus is closely related to the extinct Ornimegalonyx.
Taxonomy
The genus Strix was introduced by the Swedish naturalist Carl Linnaeus in 1758 in the tenth edition of his Systema Naturae. The type species is the tawny owl. The genus name is a Latin word meaning "owl".
Some Neotropical species were formerly classified in a separate genus, Ciccaba, which was eventually merged based on the placement of its type species, Strix huhula. | Strix (bird) | Wikipedia | 302 | 4093158 | https://en.wikipedia.org/wiki/Strix%20%28bird%29 | Biology and health sciences | Strigiformes | Animals |
Species
The genus contains 22 species:
Spotted wood owl, S. seloputo
Mottled wood owl, S. ocellata
Brown wood owl, S. leptogrammica
Tawny owl, S. aluco
Maghreb owl, S. mauritanica
Himalayan owl, S. nivicolum
Desert owl, S. hadorami
Omani owl, S. butleri
Spotted owl, S. occidentalis
Barred owl, S. varia
Cinereous owl, S. sartorii
Fulvous owl, S. fulvescens
Rusty-barred owl, S. hylophila
Chaco owl, S. chacoensis
Rufous-legged owl, S. rufipes
Ural owl, S. uralensis
Great grey owl, S. nebulosa
African wood owl, S. woodfordii
Mottled owl, S. virgata
Black-and-white owl, S. nigrolineata
Black-banded owl, S. huhula
Rufous-banded owl, S. albitarsis
Fossil species
The genus Strix is well represented in the fossil record. Being a fairly generic type of strigid owl, they were probably the first truly modern Strigidae to evolve. However, whether several of the species usually placed in this genus indeed belong here is uncertain.
Generally accepted in Strix are:
S. dakota (Early Miocene of South Dakota, USA) – tentatively placed here
Strix sp. (Late Miocene of Nebraska, USA)
Strix sp. (Late Pliocene of Rębielice Królewski, Poland) apparently similar to the great grey owl
Strix intermedia (Early - Middle Pleistocene of EC Europe) – may be paleosubspecies of S. aluco
Strix brea (Late Pleistocene of SW North America) Now placed in its own genus. (See below)
Strix sp. (Late Pleistocene of Ladds, USA)
"Strix" wintershofensis (Early/Middle Miocene of Wintershof West, Germany) and "Strix" edwardsi (Middle Miocene of Grive-Saint-Alban, France), while being strigid owls, have not at present been reliably identified to genus; they might also belong into the European Ninox-like group. | Strix (bird) | Wikipedia | 487 | 4093158 | https://en.wikipedia.org/wiki/Strix%20%28bird%29 | Biology and health sciences | Strigiformes | Animals |
"Strix" ignota (Middle Miocene of Sansan, France) is sometimes erroneously considered a nomen nudum, but this assumption is based on what appears to be a lapsus or misprint in a 1912 source. It may well belong into the present genus, but this requires confirmation.
"Strix" perpasta (Late Miocene – Early Pliocene of Gargano Peninsula, Italy) does not appear to belong into this genus either. It is sometimes considered a junior synonym of a brown fish-owl paleosubspecies.
UMMP V31030, a coracoid from Late Pliocene Rexroad Formation deposits of Kansas (USA), cannot be conclusively assigned to either the present genus or Bubo.
Extinct forms formerly in Strix:
"Strix" antiqua – now in Prosybris
"Strix" brea - now Oraristrix brea
"Strix" brevis – now in Intutula
"Strix" collongensis – now in Alasio
"Strix" melitensis and "Strix" sanctialbani – now in Tyto
"Strix" murivora – male of the Rodrigues scops owl
"Strix" newtoni and "Strix" sauzieri – male and female of the Mauritius scops owl | Strix (bird) | Wikipedia | 277 | 4093158 | https://en.wikipedia.org/wiki/Strix%20%28bird%29 | Biology and health sciences | Strigiformes | Animals |
An oil tanker, also known as a petroleum tanker, is a ship designed for the bulk transport of oil or its products. There are two basic types of oil tankers: crude tankers and product tankers. Crude tankers move large quantities of unrefined crude oil from its point of extraction to refineries. Product tankers, generally much smaller, are designed to move refined products from refineries to points near consuming markets.
Oil tankers are often classified by their size as well as their occupation. The size classes range from inland or coastal tankers of a few thousand metric tons of deadweight (DWT) to ultra-large crude carriers (ULCCs) of . Tankers move approximately of oil every year. Second only to pipelines in terms of efficiency, the average cost of transport of crude oil by tanker amounts to only US.
Some specialized types of oil tankers have evolved. One of these is the naval replenishment oiler, a tanker which can fuel a moving vessel. Combination ore-bulk-oil carriers and permanently moored floating storage units are two other variations on the standard oil tanker design. Oil tankers have been involved in a number of damaging and high-profile oil spills.
History
The technology of oil transportation has evolved alongside the oil industry. Although human use of oil reaches to prehistory, the first modern commercial exploitation dates back to James Young's manufacture of paraffin in 1850. In the early 1850s, oil began to be exported from Upper Burma, then a British colony. The oil was moved in earthenware vessels to the river bank where it was then poured into boat holds for transportation to Britain.
In the 1860s, Pennsylvania oil fields became a major supplier of oil, and a center of innovation after Edwin Drake had struck oil near Titusville, Pennsylvania. Break-bulk boats and barges were originally used to transport Pennsylvania oil in wooden barrels. But transport by barrel had several problems. The first problem was weight: they weighed , representing 20% of the total weight of a full barrel. Other problems with barrels were their expense, their tendency to leak, and the fact that they were generally used only once. The expense was significant: for example, in the early years of the Russian oil industry, barrels accounted for half the cost of petroleum production. | Oil tanker | Wikipedia | 467 | 15923603 | https://en.wikipedia.org/wiki/Oil%20tanker | Technology | Naval transport | null |
Early designs
In 1863, two sail-driven tankers were built on England's River Tyne. These were followed in 1873 by the first oil-tank steamer, Vaderland (Fatherland), which was built by Palmers Shipbuilding and Iron Company for Belgian owners. The vessel's use was curtailed by US and Belgian authorities citing safety concerns. By 1871, the Pennsylvania oil fields were making limited use of oil tank barges and cylindrical railroad tank-cars similar to those in use today.
Modern oil tankers
The modern oil tanker was developed in the period from 1877 to 1885. In 1876, Ludvig and Robert Nobel, brothers of Alfred Nobel, founded Branobel (short for Brothers Nobel) in Baku, Azerbaijan. It was, during the late 19th century, one of the largest oil companies in the world.
Ludvig was a pioneer in the development of early oil tankers. He first experimented with carrying oil in bulk on single-hulled barges. Turning his attention to self-propelled tankships, he faced a number of challenges. A primary concern was to keep the cargo and fumes well away from the engine room to avoid fires. Other challenges included allowing for the cargo to expand and contract due to temperature changes, and providing a method to ventilate the tanks.
The first successful oil tanker was Zoroaster, built by Sven Alexander Almqvist in Motala Verkstad, which carried its of kerosene cargo in two iron tanks joined by pipes. One tank was forward of the midships engine room and the other was aft. The ship also featured a set of 21 vertical watertight compartments for extra buoyancy. The ship had a length overall of , a beam of , and a draft of . Unlike later Nobel tankers, the Zoroaster design was built small enough to sail from Sweden to the Caspian by way of the Baltic Sea, Lake Ladoga, Lake Onega, the Rybinsk and Mariinsk Canals and the Volga River. The aft and the stern was put together and then dismantled to make room for the mid-section as the Caspian Sea was reached. | Oil tanker | Wikipedia | 434 | 15923603 | https://en.wikipedia.org/wiki/Oil%20tanker | Technology | Naval transport | null |
In 1883, oil tanker design took a large step forward. Working for the Nobel company, British engineer Colonel Henry F. Swan designed a set of three Nobel tankers. Instead of one or two large holds, Swan's design used several holds which spanned the width, or beam, of the ship. These holds were further subdivided into port and starboard sections by a longitudinal bulkhead. Earlier designs suffered from stability problems caused by the free surface effect, where oil sloshing from side to side could cause a ship to capsize. But this approach of dividing the ship's storage space into smaller tanks virtually eliminated free-surface problems. This approach, almost universal today, was first used by Swan in the Nobel tankers Blesk, Lumen, and Lux.
Others point to , another design of Colonel Swan, as being the first modern oil tanker. It adopted the best practices from previous oil tanker designs to create the prototype for all subsequent vessels of the type. It was the first dedicated steam-driven ocean-going tanker in the world and was the first ship in which oil could be pumped directly into the vessel hull instead of being loaded in barrels or drums. It was also the first tanker with a horizontal bulkhead; its features included cargo valves operable from the deck, cargo main piping, a vapor line, cofferdams for added safety, and the ability to fill a ballast tank with seawater when empty of cargo. The ship was built in Britain, and was purchased by Wilhelm Anton Riedemann, an agent for the Standard Oil Company along with several of her sister ships. After Glückauf was lost in 1893 after being grounded in fog, Standard Oil purchased the sister ships.
Asian trade
The 1880s also saw the beginnings of the Asian oil trade. The idea that led to moving Russian oil to the Far East via the Suez Canal was the brainchild of two men: importer Marcus Samuel and shipowner/broker Fred Lane. Prior bids to move oil through the canal had been rejected by the Suez Canal Company as being too risky. Samuel approached the problem a different way: asking the company for the specifications of a tanker it would allow through the canal.
Armed with the canal company's specifications, Samuel ordered three tankers from William Gray & Company in northern England. Named , Conch and Clam, each had a capacity of 5,010 long tons of deadweight. These three ships were the first tankers of the Tank Syndicate, forerunner of today's Royal Dutch Shell company. | Oil tanker | Wikipedia | 511 | 15923603 | https://en.wikipedia.org/wiki/Oil%20tanker | Technology | Naval transport | null |
With facilities prepared in Jakarta, Singapore, Bangkok, Saigon, Hong Kong, Shanghai, and Kobe, the fledgling Shell company was ready to become Standard Oil's first challenger in the Asian market. On August 24, 1892, Murex became the first tanker to pass through the Suez Canal. By the time Shell merged with Royal Dutch Petroleum in 1907, the company had 34 steam-driven oil tankers, compared to Standard Oil's four case-oil steamers and 16 sailing tankers.
The supertanker era
Until 1956, tankers were designed to be able to navigate the Suez Canal. This size restriction became much less of a priority after the closing of the canal during the Suez Crisis of 1956. Forced to move oil around the Cape of Good Hope, shipowners realized that bigger tankers were the key to more efficient transport. While a typical T2 tanker of the World War II era was long and had a capacity of , the ultra-large crude carriers (ULCC) built in the 1970s were over long and had a capacity of . Several factors encouraged this growth. Hostilities in the Middle East which interrupted traffic through the Suez Canal contributed, as did nationalization of Middle East oil refineries. Fierce competition among shipowners also played a part. But apart from these considerations is a simple economic advantage: the larger an oil tanker is, the more cheaply it can move crude oil, and the better it can help meet growing demands for oil.
In 1955 the world's largest supertanker was and : SS Spyros Niarchos launched that year by Vickers Armstrongs Shipbuilders Ltd in England for Greek shipping magnate Stavros Niarchos.
In 1958 United States shipping magnate Daniel K. Ludwig broke the record of 100,000 long tons of heavy displacement. His Universe Apollo displaced 104,500 long tons, a 23% increase from the previous record-holder, Universe Leader which also belonged to Ludwig. The first tanker over 100,000 dwt built in Europe was the British Admiral. The ship was launched at Barrow-in-Furness in 1965 by Elizabeth II.
The world's largest supertanker was built in 1979 at the Oppama shipyard by Sumitomo Heavy Industries, Ltd., named Seawise Giant. This ship was built with a capacity of , a length overall of and a draft of . She had 46 tanks, of deck, and at her full load draft, could not navigate the English Channel. | Oil tanker | Wikipedia | 501 | 15923603 | https://en.wikipedia.org/wiki/Oil%20tanker | Technology | Naval transport | null |
Seawise Giant was renamed Happy Giant in 1989, Jahre Viking in 1991, and Knock Nevis in 2004 (when she was converted into a permanently moored storage tanker). In 2009 she was sold for the last time, renamed Mont, and scrapped.
As of 2011, the world's two largest working supertankers are the s TI Europe and TI Oceania. These ships were built in 2002 and 2003 as Hellespont Alhambra and Hellespont Tara for the Greek Hellespont Steamship Corporation. Hellespont sold these ships to Overseas Shipholding Group and Euronav in 2004. Each of the sister ships has a capacity of over , a length overall of and a cargo capacity of . They were the first ULCCs to be double-hulled. To differentiate them from smaller ULCCs, these ships are sometimes given the V-Plus size designation.
With the exception of the pipeline, the tanker is the most cost-effective way to move oil today. Worldwide, tankers carry some annually, and the cost of transportation by tanker amounts to only US$0.02 per gallon at the pump.
Size categories
In 1954, Shell Oil developed the "average freight rate assessment" (AFRA) system which classifies tankers of different sizes. To make it an independent instrument, Shell consulted the London Tanker Brokers' Panel (LTBP). At first, they divided the groups as General Purpose for tankers under ; Medium Range for ships between 25,000 and 45,000 DWT and Long Range for the then-enormous ships that were larger than 45,000 DWT. The ships became larger during the 1970s, which prompted rescaling.
The system was developed for tax reasons as the tax authorities wanted evidence that the internal billing records were correct. Before the New York Mercantile Exchange started trading crude oil futures in 1983, it was difficult to determine the exact price of oil, which could change with every contract. Shell and BP, the first companies to use the system, abandoned the AFRA system in 1983, later followed by the US oil companies. However, the system is still used today. Besides that, there is the flexible market scale, which takes typical routes and lots of .
Merchant oil tankers carry a wide range of hydrocarbon liquids ranging from crude oil to refined petroleum products. Crude carriers are among the largest, ranging from 55,000 DWT Panamax-sized vessels to ultra-large crude carriers (ULCCs) of over 440,000 DWT. | Oil tanker | Wikipedia | 512 | 15923603 | https://en.wikipedia.org/wiki/Oil%20tanker | Technology | Naval transport | null |
Smaller tankers, ranging from well under 10,000 DWT to 80,000 DWT Panamax vessels, generally carry refined petroleum products, and are known as product tankers. The smallest tankers, with capacities under 10,000 DWT generally work near-coastal and inland waterways. Although they were in the past, ships of the smaller Aframax and Suezmax classes are no longer regarded as supertankers.
VLCC and ULCC
"Supertankers" are the largest oil tankers, and the largest mobile man-made structures. They include very large and ultra-large crude carriers (VLCCs and ULCCs – see above) with capacities over 250,000 DWT. These ships can transport of oil/318,000 metric tons. By way of comparison, the United Kingdom consumed about of oil per day in 2009. ULCCs commissioned in the 1970s were the largest vessels ever built, but have all now been scrapped. A few newer ULCCs remain in service, none of which are more than 400 meters long.
Because of their size, supertankers often cannot enter port fully loaded. These ships can take on their cargo at offshore platforms and single-point moorings. On the other end of the journey, they often pump their cargo off to smaller tankers at designated lightering points off-coast. Supertanker routes are typically long, requiring them to stay at sea for extended periods, often around seventy days at a time.
Chartering
The act of hiring a ship to carry cargo is called chartering. (The contract itself is known as a charter party.) Tankers are hired by four types of charter agreements: the voyage charter, the time charter, the bareboat charter, and contract of affreightment. In a voyage charter the charterer rents the vessel from the loading port to the discharge port. In a time charter the vessel is hired for a set period of time, to perform voyages as the charterer directs. In a bareboat charter the charterer acts as the ship's operator and manager, taking on responsibilities such as providing the crew and maintaining the vessel. Finally, in a contract of affreightment or COA, the charterer specifies a total volume of cargo to be carried in a specific time period and in specific sizes, for example a COA could be specified as of JP-5 in a year's time in shipments. | Oil tanker | Wikipedia | 492 | 15923603 | https://en.wikipedia.org/wiki/Oil%20tanker | Technology | Naval transport | null |
One of the key aspects of any charter party is the freight rate, or the price specified for carriage of cargo. The freight rate of a tanker charter party is specified in one of four ways: by a lump sum rate, by rate per ton, by a time charter equivalent rate, or by Worldscale rate. In a lump sum rate arrangement, a fixed price is negotiated for the delivery of a specified cargo, and the ship's owner/operator is responsible to pay for all port costs and other voyage expenses. Rate per ton arrangements are used mostly in chemical tanker chartering, and differ from lump sum rates in that port costs and voyage expenses are generally paid by the charterer. Time charter arrangements specify a daily rate, and port costs and voyage expenses are also generally paid by the charterer.
The Worldwide Tanker Normal Freight Scale, often referred to as Worldscale, is established and governed jointly by the Worldscale Associations of London and New York. Worldscale establishes a baseline price for carrying a metric ton of product between any two ports in the world. In Worldscale negotiations, operators and charterers will determine a price based on a percentage of the Worldscale rate. The baseline rate is expressed as WS 100. If a given charter party settled on 85% of the Worldscale rate, it would be expressed as WS 85. Similarly, a charter party set at 125% of the Worldscale rate would be expressed as WS 125.
Recent markets
The market is affected by a wide variety of variables such as the supply and demand of oil as well as the supply and demand of oil tankers. Some particular variables include winter temperatures, excess tanker tonnage, supply fluctuations in the Persian Gulf, and interruptions in refinery services.
In 2006, time-charters tended towards long term. Of the time charters executed in that year, 58% were for a period of 24 or more months, 14% were for periods of 12 to 24 months, 4% were from 6 to 12 months, and 24% were for periods of less than 6 months. | Oil tanker | Wikipedia | 421 | 15923603 | https://en.wikipedia.org/wiki/Oil%20tanker | Technology | Naval transport | null |
From 2003, the demand for new ships started to grow, resulting in 2007 in a record breaking order backlog for shipyards, exceeding their capacity with rising newbuilding prices as a result. This resulted in a glut of ships when demand dropped due to a weakened global economy and dramatically reduced demand in the United States. The charter rate for very large crude carriers, which carry two million barrels of oil, had peaked at $309,601 per day in 2007 but had dropped to $7,085 per day by 2012, far below the operating costs of these ships. As a result, several tanker operators laid up their ships. Prices rose significantly in 2015 and early 2016, but delivery of new tankers was projected to keep prices in check.
Owners of large oil tanker fleets include Teekay Corporation, A P Moller Maersk, DS Torm, Frontline, MOL Tankship Management, Overseas Shipholding Group, and Euronav.
Fleet characteristics
In 2005, oil tankers made up 36.9% of the world's fleet in terms of deadweight tonnage. The world's total oil tankers deadweight tonnage has increased from in 1970 to in 2005. The combined deadweight tonnage of oil tankers and bulk carriers, represents 72.9% of the world's fleet.
Cargo movement
In 2005, 2.42 billion metric tons of oil were shipped by tanker. 76.7% of this was crude oil, and the rest consisted of refined petroleum products. This amounted to 34.1% of all seaborne trade for the year. Combining the amount carried with the distance it was carried, oil tankers moved 11,705 billion metric-ton-miles of oil in 2005.
By comparison, in 1970 1.44 billion metric tons of oil were shipped by tanker. This amounted to 34.1% of all seaborne trade for that year. In terms of amount carried and distance carried, oil tankers moved 6,487 billion metric-ton-miles of oil in 1970.
The United Nations also keeps statistics about oil tanker productivity, stated in terms of metric tons carried per metric ton of deadweight as well as metric-ton-miles of carriage per metric ton of deadweight. In 2005, for each of oil tankers, 6.7 metric tons of cargo was carried. Similarly, each of oil tankers was responsible for 32,400 metric-ton miles of carriage. | Oil tanker | Wikipedia | 495 | 15923603 | https://en.wikipedia.org/wiki/Oil%20tanker | Technology | Naval transport | null |
The main loading ports in 2005 were located in Western Asia, Western Africa, North Africa, and the Caribbean, with 196.3, 196.3, 130.2 and 246.6 million metric tons of cargo loaded in these regions. The main discharge ports were located in North America, Europe, and Japan with 537.7, 438.4, and 215.0 million metric tons of cargo discharged in these regions.
Flag states
International law requires that every merchant ship be registered in a country, called its flag state. A ship's flag state exercises regulatory control over the vessel and is required to inspect it regularly, certify the ship's equipment and crew, and issue safety and pollution prevention documents. As of 2007, the United States Central Intelligence Agency statistics count 4,295 oil tankers of or greater worldwide. Panama was the world's largest flag state for oil tankers, with 528 of the vessels in its registry. Six other flag states had more than 200 registered oil tankers: Liberia (464), Singapore (355), China (252), Russia (250), the Marshall Islands (234) and the Bahamas (209). The Panamanian, Liberian, Marshallese and Bahamian flags are open registries and considered by the International Transport Workers' Federation to be flags of convenience. By comparison, the United States and the United Kingdom only had 59 and 27 registered oil tankers, respectively.
Vessel life cycle
In 2005, the average age of oil tankers worldwide was 10 years. Of these, 31.6% were under 4 years old and 14.3% were over 20 years old. In 2005, 475 new oil tankers were built, accounting for . The average size for these new tankers was . Nineteen of these were VLCC size, 19 were Suezmax, 51 were Aframax, and the rest were smaller designs. By comparison, , , and worth of oil tanker capacity was built in 1980, 1990, and 2000 respectively. | Oil tanker | Wikipedia | 408 | 15923603 | https://en.wikipedia.org/wiki/Oil%20tanker | Technology | Naval transport | null |
Ships are generally removed from the fleet through a process known as scrapping. Ship-owners and buyers negotiate scrap prices based on factors such as the ship's empty weight (called light ton displacement or LDT) and prices in the scrap metal market. In 1998, almost 700 ships went through the scrapping process at shipbreakers in places such as Gadani, Alang and Chittagong. In 2004 and 2005, and respectively of oil tankers were scrapped. Between 2000 and 2005, the capacity of oil tankers scrapped each year has ranged between and . In this same timeframe, tankers have accounted for between 56.5% and 90.5% of the world's total scrapped ship tonnage. In this period the average age of scrapped oil tankers has ranged from 26.9 to 31.5 years.
Vessel pricing
In 2005, the price for new oil tankers in the , , and ranges were $43 million, $58 million, and $120 million respectively. In 1985 these vessels would have cost $18 million, $22 million, and $47 million respectively.
Oil tankers are often sold second hand. In 2005, worth of oil tankers were sold used. Some representative prices for that year include $42.5 million for a tanker, $60.7 million for a , $73 million for a , and $116 million for tanker. For a concrete example, in 2006, Bonheur subsidiary First Olsen paid $76.5 million for Knock Sheen, a 159,899 DWT tanker.
The cost of operating the largest tankers, the Very Large Crude Carriers, is currently between $10,000 and $12,000 per day.
Current structural design
Oil tankers generally have from 8 to 12 tanks. Each tank is split into two or three independent compartments by fore-and-aft bulkheads. The tanks are numbered with tank one being the forwardmost. Individual compartments are referred to by the tank number and the athwartships position, such as "one port", "three starboard", or "six center".
A cofferdam is a small space left open between two bulkheads, to give protection from heat, fire, or collision. Tankers generally have cofferdams forward and aft of the cargo tanks, and sometimes between individual tanks. A pumproom houses all the pumps connected to a tanker's cargo lines. Some larger tankers have two pumprooms. A pumproom generally spans the total breadth of the ship.
Hull designs | Oil tanker | Wikipedia | 511 | 15923603 | https://en.wikipedia.org/wiki/Oil%20tanker | Technology | Naval transport | null |
A major component of tanker architecture is the design of the hull or outer structure. A tanker with a single outer shell between the product and the ocean is said to be "single-hulled". Most newer tankers are "double hulled", with an extra space between the hull and the storage tanks. Hybrid designs such as "double-bottom" and "double-sided" combine aspects of single and double-hull designs. All single-hulled tankers around the world will be phased out by 2026, in accordance with the International Convention for the Prevention of Pollution from Ships, 1973 (MARPOL). The United Nations has decided to phase out single hull oil tankers by 2010.
In 1998, the Marine Board of the National Academy of Sciences conducted a survey of industry experts regarding the pros and cons of double-hull design. Some of the advantages of the double-hull design that were mentioned include ease of ballasting in emergency situations, reduced practice of saltwater ballasting in cargo tanks decreases corrosion, increased environmental protection, cargo discharge is quicker, more complete and easier, tank washing is more efficient, and better protection in low-impact collisions and grounding.
The same report lists the following as some drawbacks to the double-hull design, including higher build costs, greater operating expenses (e.g. higher canal and port tariffs), difficulties in ballast tank ventilation, the fact that ballast tanks need continuous monitoring and maintenance, increased transverse free surface, the greater number of surfaces to maintain, the risk of explosions in double-hull spaces if a vapor detection system not fitted, and that cleaning ballast tanks is more difficult for double hull ships.
In all, double-hull tankers are said to be safer than a single-hull in a grounding incident, especially when the shore is not very rocky. The safety benefits are less clear on larger vessels and in cases of high speed impact.
Although double-hull design is superior in low energy casualties and prevents spillage in small casualties, in high energy casualties where both hulls are breached, oil can spill through the double-hull and into the sea and spills from a double-hull tanker can be significantly higher than designs like the mid-deck tanker, the Coulombi Egg Tanker and even a pre-MARPOL tanker, as the last one has a lower oil column and reaches hydrostatic balance sooner. | Oil tanker | Wikipedia | 483 | 15923603 | https://en.wikipedia.org/wiki/Oil%20tanker | Technology | Naval transport | null |
Inert gas system
An oil tanker's inert gas system is one of the most important parts of its design. Fuel oil itself is very difficult to ignite, but its hydrocarbon vapors are explosive when mixed with air in certain concentrations. The purpose of the system is to create an atmosphere inside tanks in which the hydrocarbon oil vapors cannot burn.
As inert gas is introduced into a mixture of hydrocarbon vapors and air, it increases the lower flammable limit or lowest concentration at which the vapors can be ignited. At the same time it decreases the upper flammable limit or highest concentration at which the vapors can be ignited. When the total concentration of oxygen in the tank decreases to about 11%, the upper and lower flammable limits converge and the flammable range disappears.
Inert gas systems deliver air with an oxygen concentration of less than 5% by volume. As a tank is pumped out, it is filled with inert gas and kept in this safe state until the next cargo is loaded. The exception is in cases when the tank must be entered. Safely gas-freeing a tank is accomplished by purging hydrocarbon vapors with inert gas until the hydrocarbon concentration inside the tank is under about 1%. Thus, as air replaces the inert gas, the concentration cannot rise to the lower flammable limit and is safe.
Cargo operations
Operations aboard oil tankers are governed by an established body of best practices and a large body of international law. Cargo can be moved on or off of an oil tanker in several ways. One method is for the ship to moor alongside a pier, connect with cargo hoses or marine loading arms. Another method involves mooring to offshore buoys, such as a single point mooring, and making a cargo connection via underwater cargo hoses. A third method is by ship-to-ship transfer, also known as lightering. In this method, two ships come alongside in open sea and oil is transferred manifold to manifold via flexible hoses. Lightering is sometimes used where a loaded tanker is too large to enter a specific port. | Oil tanker | Wikipedia | 431 | 15923603 | https://en.wikipedia.org/wiki/Oil%20tanker | Technology | Naval transport | null |
Pre-transfer preparation
Prior to any transfer of cargo, the chief officer must develop a transfer plan detailing specifics of the operation such as how much cargo will be moved, which tanks will be cleaned, and how the ship's ballasting will change. The next step before a transfer is the pretransfer conference. The pretransfer conference covers issues such as what products will be moved, the order of movement, names and titles of key people, particulars of shipboard and shore equipment, critical states of the transfer, regulations in effect, emergency and spill-containment procedures, watch and shift arrangements, and shutdown procedures.
After the conference is complete, the person in charge on the ship and the person in charge of the shore installation go over a final inspection checklist. In the United States, the checklist is called a Declaration of Inspection or DOI. Outside the US, the document is called the "Ship/Shore Safety Checklist." Items on the checklist include proper signals and signs are displayed, secure mooring of the vessel, choice of language for communication, securing of all connections, that emergency equipment is in place, and that no repair work is taking place.
Loading cargo
Loading an oil tanker consists primarily of pumping cargo into the ship's tanks. As oil enters the tank, the vapors inside the tank must be somehow expelled. Depending on local regulations, the vapors can be expelled into the atmosphere or discharged back to the pumping station by way of a vapor recovery line. It is also common for the ship to move water ballast during the loading of cargo to maintain proper trim.
Loading starts slowly at a low pressure to ensure that equipment is working correctly and that connections are secure. Then a steady pressure is achieved and held until the "topping-off" phase when the tanks are nearly full. Topping off is a very dangerous time in handling oil, and the procedure is handled particularly carefully. Tank-gauging equipment is used to tell the person in charge how much space is left in the tank, and all tankers have at least two independent methods for tank-gauging. As the tanker becomes full, crew members open and close valves to direct the flow of product and maintain close communication with the pumping facility to decrease and finally stop the flow of liquid.
Unloading cargo | Oil tanker | Wikipedia | 467 | 15923603 | https://en.wikipedia.org/wiki/Oil%20tanker | Technology | Naval transport | null |
The process of moving oil off of a tanker is similar to loading, but has some key differences. The first step in the operation is following the same pretransfer procedures as used in loading. When the transfer begins, it is the ship's cargo pumps that are used to move the product ashore. As in loading, the transfer starts at low pressure to ensure that equipment is working correctly and that connections are secure. Then a steady pressure is achieved and held during the operation. While pumping, tank levels are carefully watched and key locations, such as the connection at the cargo manifold and the ship's pumproom are constantly monitored. Under the direction of the person in charge, crew members open and close valves to direct the flow of product and maintain close communication with the receiving facility to decrease and finally stop the flow of liquid.
Tank cleaning
Tanks must be cleaned from time to time for various reasons. One reason is to change the type of product carried inside a tank. Also, when tanks are to be inspected or maintenance must be performed within a tank, it must be not only cleaned, but made gas-free.
On most crude-oil tankers, a special crude oil washing (COW) system is part of the cleaning process. The COW system circulates part of the cargo through the fixed tank-cleaning system to remove wax and asphaltic deposits. Tanks that carry less viscous cargoes are washed with water. Fixed and portable automated tank cleaning machines, which clean tanks with high-pressure water jets, are widely used. Some systems use rotating high-pressure water jets to spray hot water on all the internal surfaces of the tank. As the spraying takes place, the liquid is pumped out of the tank. | Oil tanker | Wikipedia | 346 | 15923603 | https://en.wikipedia.org/wiki/Oil%20tanker | Technology | Naval transport | null |
After a tank is cleaned, provided that it is going to be prepared for entry, it will be purged. Purging is accomplished by pumping inert gas into the tank until hydrocarbons have been sufficiently expelled. Next the tank is gas freed which is usually accomplished by blowing fresh air into the space with portable air powered or water powered air blowers. "Gas freeing" brings the oxygen content of the tank up to 20.8% O2. The inert gas buffer between fuel and oxygen atmospheres ensures they are never capable of ignition. Specially trained personnel monitor the tank's atmosphere, often using hand-held gas indicators which measure the percentage of hydrocarbons present. After a tank is gas-free, it may be further hand-cleaned in a manual process known as mucking. Mucking requires protocols for entry into confined spaces, protective clothing, designated safety observers, and possibly the use of airline respirators.
Special-use oil tankers
Some sub-types of oil tankers have evolved to meet specific military and economic needs. These sub-types include naval replenishment ships, oil-bulk-ore combination carriers, floating storage and offloading units (FSOs) and floating production storage and offloading units (FPSOs).
Replenishment ships
Replenishment ships, known as oilers in the United States and fleet tankers in Commonwealth countries, are ships that can provide oil products to naval vessels while on the move. This process, called underway replenishment, extends the length of time a naval vessel can stay at sea, as well as her effective range. Prior to underway replenishment, naval vessels had to enter a port or anchor to take on fuel. In addition to fuel, replenishment ships may also deliver water, ammunition, rations, stores and personnel.
Ore-bulk-oil carriers
An ore-bulk-oil carrier, also known as combination carrier or OBO, is a ship designed to be capable of carrying wet or dry bulk cargoes. This design was intended to provide flexibility in two ways. Firstly, an OBO would be able to switch between the dry and wet bulk trades based on market conditions. Secondly, an OBO could carry oil on one leg of a voyage and return carrying dry bulk, reducing the number of unprofitable ballast voyages it would have to make. | Oil tanker | Wikipedia | 477 | 15923603 | https://en.wikipedia.org/wiki/Oil%20tanker | Technology | Naval transport | null |
In practice, the flexibility which the OBO design allows has gone largely unused, as these ships tend to specialize in either the liquid or dry bulk trade. Also, these ships have endemic maintenance problems. On one hand, due to a less specialized design, an OBO suffers more from wear and tear during dry cargo onload than a bulker. On the other hand, components of the liquid cargo system, from pumps to valves to piping, tend to develop problems when subjected to periods of disuse. These factors have contributed to a steady reduction in the number of OBO ships worldwide since the 1970s.
One of the more famous OBOs was of which in September 1980 became the largest British ship ever lost at sea. It sank in a Pacific typhoon while carrying a cargo of iron ore from Canada to Japan.
Floating storage units
Floating storage and offloading units (FSO) are used worldwide by the offshore oil industry to receive oil from nearby platforms and store it until it can be offloaded onto oil tankers. A similar system, the floating production storage and offloading unit (FPSO), has the ability to process the product while it is on board. These floating units reduce oil production costs and offer mobility, large storage capacity, and production versatility.
FPSO and FSOs are often created out of old, stripped-down oil tankers, but can be made from new-built hulls; Shell España first used a tanker as an FPSO in August 1977. An example of an FSO that used to be an oil tanker is the Knock Nevis. These units are usually moored to the seabed through a spread mooring system. A turret-style mooring system can be used in areas prone to severe weather. This turret system lets the unit rotate to minimize the effects of sea-swell and wind.
Pollution
Oil spills have devastating effects on the environment. Crude oil contains polycyclic aromatic hydrocarbons (PAHs) which are very difficult to clean up, and last for years in the sediment and marine environment. Marine species constantly exposed to PAHs can exhibit developmental problems, susceptibility to disease, and abnormal reproductive cycles. | Oil tanker | Wikipedia | 443 | 15923603 | https://en.wikipedia.org/wiki/Oil%20tanker | Technology | Naval transport | null |
By the sheer amount of oil carried, modern oil tankers can be a threat to the environment. As discussed above, a VLCC tanker can carry of crude oil. This is about eight times the amount spilled in the widely known Exxon Valdez incident. In this spill, the ship ran aground and dumped of oil into the ocean in March 1989. Despite efforts of scientists, managers, and volunteers, over 400,000 seabirds, about 1,000 sea otters, and immense numbers of fish were killed. Considering the volume of oil carried by sea, however, tanker owners' organizations often argue that the industry's safety record is excellent, with only a tiny fraction of a percentage of oil cargoes carried ever being spilled. The International Association of Independent Tanker Owners has observed that "accidental oil spills this decade have been at record low levels—one third of the previous decade and one tenth of the 1970s—at a time when oil transported has more than doubled since the mid 1980s."
Oil tankers are only one source of oil spills. According to the United States Coast Guard, 35.7% of the volume of oil spilled in the United States from 1991 to 2004 came from tank vessels (ships/barges), 27.6% from facilities and other non-vessels, 19.9% from non-tank vessels, 9.3% from pipelines, and 7.4% from mystery spills. Only 5% of the actual spills came from oil tankers, while 51.8% came from other kinds of vessels. The detailed statistics for 2004 show tank vessels responsible for somewhat less than 5% of the number of total spills but more than 60% of the volume. Tanker spills are much more rare and much more serious than spills from non-tank vessels.
The International Tanker Owners Pollution Federation has tracked 9,351 accidental spills that have occurred since 1974. According to this study, most spills result from routine operations such as loading cargo, discharging cargo, and taking on fuel oil. 91% of the operational oil spills are small, resulting in less than 7 metric tons per spill. On the other hand, spills resulting from accidents like collisions, groundings, hull failures, and explosions are much larger, with 84% of these involving losses of over 700 metric tons. | Oil tanker | Wikipedia | 474 | 15923603 | https://en.wikipedia.org/wiki/Oil%20tanker | Technology | Naval transport | null |
Following the Exxon Valdez spill, the United States passed the Oil Pollution Act of 1990 (OPA-90), which excluded single-hull tank vessels of 5,000 gross tons or more from US waters from 2010 onward, apart from those with a double bottom or double sides, which may be permitted to trade to the United States through 2015, depending on their age. Following the sinkings of (1999) and Prestige (2002), the European Union passed its own stringent anti-pollution packages (known as Erika I, II, and III), which also require all tankers entering its waters to be double-hulled by 2010. The Erika packages are controversial because they introduced the new legal concept of "serious negligence".
Air pollution
Large ships are often run on low quality fuel oils, such as bunker oil, which is highly polluting and has been shown to be a health risk. | Oil tanker | Wikipedia | 183 | 15923603 | https://en.wikipedia.org/wiki/Oil%20tanker | Technology | Naval transport | null |
Hepatitis B is an infectious disease caused by the hepatitis B virus (HBV) that affects the liver; it is a type of viral hepatitis. It can cause both acute and chronic infection.
Many people have no symptoms during an initial infection. For others, symptoms may appear 30 to 180 days after becoming infected and can include a rapid onset of sickness with nausea, vomiting, yellowish skin, fatigue, yellow urine, and abdominal pain. Symptoms during acute infection typically last for a few weeks, though some people may feel sick for up to six months. Deaths resulting from acute stage HBV infections are rare. An HBV infection lasting longer than six months is usually considered chronic. The likelihood of developing chronic hepatitis B is higher for those who are infected with HBV at a younger age. About 90% of those infected during or shortly after birth develop chronic hepatitis B, while less than 10% of those infected after the age of five develop chronic cases. Most of those with chronic disease have no symptoms; however, cirrhosis and liver cancer eventually develop in about 25% of those with chronic HBV. | Hepatitis B | Wikipedia | 225 | 15925628 | https://en.wikipedia.org/wiki/Hepatitis%20B | Biology and health sciences | Viral diseases | Health |
The virus is transmitted by exposure to infectious blood or body fluids. In areas where the disease is common, infection around the time of birth or from contact with other people's blood during childhood are the most frequent methods by which hepatitis B is acquired. In areas where the disease is rare, intravenous drug use and sexual intercourse are the most frequent routes of infection. Other risk factors include working in healthcare, blood transfusions, dialysis, living with an infected person, travel in countries with high infection rates, and living in an institution. Tattooing and acupuncture led to a significant number of cases in the 1980s; however, this has become less common with improved sterilization. The viruses cannot be spread by holding hands, sharing eating utensils, kissing, hugging, coughing, sneezing, or breastfeeding. The infection can be diagnosed 30 to 60 days after exposure. The diagnosis is usually confirmed by testing the blood for parts of the virus and for antibodies against the virus. It is one of five main hepatitis viruses: A, B, C, D, and E. During an initial infection, care is based on a person's symptoms. In those who develop chronic disease, antiviral medication such as tenofovir or interferon may be useful; however, these drugs are expensive. Liver transplantation is sometimes recommended for cases of cirrhosis or hepatocellular carcinoma.
Hepatitis B infection has been preventable by vaccination since 1982. As of 2022, the hepatitis B vaccine is between 98% and 100% effective in preventing infection. The vaccine is administered in several doses; after an initial dose, two or three more vaccine doses are required at a later time for full effect. The World Health Organization (WHO) recommends infants receive the vaccine within 24 hours after birth when possible. National programs have made the hepatitis B vaccine available for infants in 190 countries as of the end of 2021. To further prevent infection, the WHO recommends testing all donated blood for hepatitis B before using it for transfusion. Using antiviral prophylaxis to prevent mother-to-child transmission is also recommended, as is following safe sex practices, including the use of condoms. In 2016, the WHO set a goal of eliminating viral hepatitis as a threat to global public health by 2030. Achieving this goal would require the development of therapeutic treatments to cure chronic hepatitis B, as well as preventing its transmission and using vaccines to prevent new infections. | Hepatitis B | Wikipedia | 505 | 15925628 | https://en.wikipedia.org/wiki/Hepatitis%20B | Biology and health sciences | Viral diseases | Health |
An estimated 296 million people, or 3.8% of the global population, had chronic hepatitis B infections as of 2019. Another 1.5 million developed acute infections that year, and 820,000 deaths occurred as a result of HBV. Cirrhosis and liver cancer are responsible for most HBV-related deaths. The disease is most prevalent in Africa (affecting 7.5% of the continent's population) and in the Western Pacific region (5.9%). Infection rates are 1.5% in Europe and 0.5% in the Americas. According to some estimates, about a third of the world's population has been infected with hepatitis B at one point in their lives. Hepatitis B was originally known as "serum hepatitis".
Signs and symptoms
Acute infection with virus is associated with acute viral hepatitis, an illness that begins with general ill-health, loss of appetite, nausea, vomiting, body aches, mild fever, and dark urine, and then progresses to development of jaundice. The illness lasts for a few weeks and then gradually improves in most affected people. A few people may have a more severe form of liver disease known as fulminant hepatic failure and may die as a result. The infection may be entirely asymptomatic and may go unrecognized.
Chronic infection with virus may be asymptomatic or may be associated with chronic inflammation of the liver (chronic hepatitis), leading to cirrhosis over a period of several years. This type of infection dramatically increases the incidence of hepatocellular carcinoma (HCC; liver cancer). Across Europe, hepatitis B and C cause approximately 50% of hepatocellular carcinomas. Chronic carriers are encouraged to avoid consuming alcohol as it increases their risk for cirrhosis and liver cancer. virus has been linked to the development of membranous glomerulonephritis (MGN). | Hepatitis B | Wikipedia | 401 | 15925628 | https://en.wikipedia.org/wiki/Hepatitis%20B | Biology and health sciences | Viral diseases | Health |
Symptoms outside of the liver are present in 1–10% of HBV-infected people and include serum-sickness–like syndrome, acute necrotizing vasculitis (polyarteritis nodosa), membranous glomerulonephritis, and papular acrodermatitis of childhood (Gianotti–Crosti syndrome). The serum-sickness–like syndrome occurs in the setting of acute , often preceding the onset of jaundice. The clinical features are fever, skin rash, and polyarteritis. The symptoms often subside shortly after the onset of jaundice but can persist throughout the duration of acute . About 30–50% of people with acute necrotizing vasculitis (polyarteritis nodosa) are HBV carriers. HBV-associated nephropathy has been described in adults but is more common in children. Membranous glomerulonephritis is the most common form. Other immune-mediated hematological disorders, such as essential mixed cryoglobulinemia and aplastic anemia have been described as part of the extrahepatic manifestations of HBV infection, but their association is not as well-defined; therefore, they probably should not be considered etiologically linked to HBV.
Cause
Transmission
Transmission of virus results from exposure to infectious blood or body fluids containing blood. HBV is 50 to 100 times more infectious than human immunodeficiency virus (HIV). HBV can be transmitted through several routes of infection. In vertical transmission, HBV is passed from mother to child (MTCT) during childbirth. Without intervention, a mother who is positive for HBsAg has a 20% risk of passing the infection to her offspring at the time of birth. This risk is as high as 90% if the mother is also positive for HBeAg.
Early life horizontal transmission can occur through bites, lesions, certain sanitary habits, or other contact with secretions or saliva containing HBV. Adult horizontal transmission is known to occur through sexual contact, blood transfusions and transfusion with other human blood products, re-use of contaminated needles and syringes. Breastfeeding after proper immunoprophylaxis does not appear to contribute to mother-to-child-transmission (MTCT) of HBV.
Virology
Structure | Hepatitis B | Wikipedia | 501 | 15925628 | https://en.wikipedia.org/wiki/Hepatitis%20B | Biology and health sciences | Viral diseases | Health |
virus (HBV) is a member of the hepadnavirus family. The virus particle (virion) consists of an outer lipid envelope and an icosahedral nucleocapsid core composed of core protein. These virions are 30–42 nm in diameter. The nucleocapsid encloses the viral DNA and a DNA polymerase that has reverse transcriptase activity. The outer envelope contains embedded proteins that are involved in viral binding of, and entry into, susceptible cells. The virus is one of the smallest enveloped animal viruses. The 42 nm virions, which are capable of infecting liver cells known as hepatocytes, are referred to as "Dane particles". In addition to the Dane particles, filamentous and spherical bodies lacking a core can be found in the serum of infected individuals. These particles are not infectious and are composed of the lipid and protein that forms part of the surface of the virion, which is called the surface antigens (HBsAg), and is produced in excess during the life cycle of the virus.
Genome | Hepatitis B | Wikipedia | 226 | 15925628 | https://en.wikipedia.org/wiki/Hepatitis%20B | Biology and health sciences | Viral diseases | Health |
The genome of HBV is made of circular DNA, but it is unusual because the DNA is not fully double-stranded. One end of the full length strand is linked to the HBV DNA polymerase. The genome is 3020–3320 nucleotides long (for the full-length strand) and 1700–2800 nucleotides long (for the short length-strand). The negative-sense (non-coding) is complementary to the viral mRNA. The viral DNA is found in the nucleus soon after infection of the cell. The partially double-stranded DNA is rendered fully double-stranded by completion of the (+) sense strand and removal of a protein molecule from the (−) sense strand and a short sequence of RNA from the (+) sense strand. Non-coding bases are removed from the ends of the (−) sense strand and the ends are rejoined. There are four known genes encoded by the genome, called C, X, P, and S. The core protein is coded for by gene C (HBcAg), and its start codon is preceded by an upstream in-frame AUG start codon from which the pre-core protein is produced. HBeAg is produced by proteolytic processing of the pre-core protein. In some rare strains of the virus known as hepatitis B virus precore mutants, no HBeAg is present.
The DNA polymerase is encoded by gene P. Gene S is the gene that codes for the surface antigen (HBsAg). The HBsAg gene is one long open reading frame but contains three in frame "start" (ATG) codons that divide the gene into three sections, pre-S1, pre-S2, and S. Because of the multiple start codons, polypeptides of three different sizes called large (the order from surface to the inside: pre-S1, pre-S2, and S ), middle (pre-S2, S), and small (S) are produced. There is a myristyl group, which plays an important role in infection, on the amino-terminal end of the preS1 part of the large (L) protein. In addition to that, N terminus of the L protein have virus attachment and capsid binding sites. Because of that, the N termini of half of the L protein molecules are positioned outside the membrane and the other half positioned inside the membrane. | Hepatitis B | Wikipedia | 505 | 15925628 | https://en.wikipedia.org/wiki/Hepatitis%20B | Biology and health sciences | Viral diseases | Health |
The function of the protein coded for by gene X is not fully understood but it is associated with the development of liver cancer. It stimulates genes that promote cell growth and inactivates growth regulating molecules.
Pathogenesis
The life cycle of virus is complex. is one of a few known pararetroviruses: non-retroviruses that still use reverse transcription in their replication process. The virus gains entry into the cell by binding to NTCP on the surface and being endocytosed. Because the virus multiplies via RNA made by a host enzyme, the viral genomic DNA has to be transferred to the cell nucleus by host proteins called chaperones. The partially double-stranded, circular viral DNA is then made fully double stranded by HBV DNA polymerase, transforming the genome into covalently closed circular DNA (cccDNA). This cccDNA serves as a template for transcription of four viral mRNAs by host RNA polymerase. The largest mRNA, (which is longer than the viral genome), is used to make the new copies of the genome and to make the capsid core protein and the viral DNA polymerase. These four viral transcripts undergo additional processing and go on to form progeny virions that are released from the cell or returned to the nucleus and re-cycled to produce even more copies. The long mRNA is then transported back to the cytoplasm where the virion P protein (the DNA polymerase) synthesizes DNA via its reverse transcriptase activity.
Serotypes and genotypes
The virus is divided into four major serotypes (adr, adw, ayr, ayw) based on antigenic epitopes presented on its envelope proteins, and into eight major genotypes (A–H). The genotypes have a distinct geographical distribution and are used in tracing the evolution and transmission of the virus. Differences between genotypes affect the disease severity, course and likelihood of complications, and response to treatment and possibly vaccination. There are two other genotypes I and J but they are not universally accepted as of 2015. The diversity of genotypes is not shown equally in the world. For example, A, D, and E genotypes have been seen in Africa prevalently while B and C genotypes are observed in Asia as widespread. | Hepatitis B | Wikipedia | 483 | 15925628 | https://en.wikipedia.org/wiki/Hepatitis%20B | Biology and health sciences | Viral diseases | Health |
Genotypes differ by at least 8% of their sequence and were first reported in 1988 when six were initially described (A–F). Two further types have since been described (G and H). Most genotypes are now divided into subgenotypes with distinct properties.
Mechanisms
virus primarily interferes with the functions of the liver by replicating in hepatocytes. A functional receptor is NTCP. There is evidence that the receptor in the closely related duck hepatitis B virus is carboxypeptidase D. The virions bind to the host cell via the preS domain of the viral surface antigen and are subsequently internalized by endocytosis. HBV-preS-specific receptors are expressed primarily on hepatocytes; however, viral DNA and proteins have also been detected in extrahepatic sites, suggesting that cellular receptors for HBV may also exist on extrahepatic cells.
During HBV infection, the host immune response causes both hepatocellular damage and viral clearance. Although the innate immune response does not play a significant role in these processes, the adaptive immune response, in particular virus-specific cytotoxic T lymphocytes(CTLs), contributes to most of the liver injury associated with HBV infection. CTLs eliminate HBV infection by killing infected cells and producing antiviral cytokines, which are then used to purge HBV from viable hepatocytes. Although liver damage is initiated and mediated by the CTLs, antigen-nonspecific inflammatory cells can worsen CTL-induced immunopathology, and platelets activated at the site of infection may facilitate the accumulation of CTLs in the liver.
Diagnosis
The tests, called assays, for detection of virus infection involve serum or blood tests that detect either viral antigens (proteins produced by the virus) or antibodies produced by the host. Interpretation of these assays is complex. | Hepatitis B | Wikipedia | 401 | 15925628 | https://en.wikipedia.org/wiki/Hepatitis%20B | Biology and health sciences | Viral diseases | Health |
The surface antigen (HBsAg) is most frequently used to screen for the presence of this infection. It is the first detectable viral antigen to appear during infection. However, early in an infection, this antigen may not be present and it may be undetectable later in the infection as it is being cleared by the host. The infectious virion contains an inner "core particle" enclosing viral genome. The icosahedral core particle is made of 180 or 240 copies of the core protein, alternatively known as core antigen, or HBcAg. During this 'window' in which the host remains infected but is successfully clearing the virus, IgM antibodies specific to the core antigen (anti-HBc IgM) may be the only serological evidence of disease. Therefore, most diagnostic panels contain HBsAg and total anti-HBc (both IgM and IgG).
Shortly after the appearance of the HBsAg, another antigen called e antigen (HBeAg) will appear. Traditionally, the presence of HBeAg in a host's serum is associated with much higher rates of viral replication and enhanced infectivity; however, variants of the virus do not produce the 'e' antigen, so this rule does not always hold true. During the natural course of an infection, the HBeAg may be cleared, and antibodies to the 'e' antigen (anti-HBe) will arise immediately afterwards. This conversion is usually associated with a dramatic decline in viral replication.
If the host is able to clear the infection, eventually the HBsAg will become undetectable and will be followed by IgG antibodies to the surface antigen and core antigen (anti-HBs and anti HBc IgG). The time between the removal of the HBsAg and the appearance of anti-HBs is called the window period. A person negative for HBsAg but positive for anti-HBs either has cleared an infection or has been vaccinated previously. | Hepatitis B | Wikipedia | 404 | 15925628 | https://en.wikipedia.org/wiki/Hepatitis%20B | Biology and health sciences | Viral diseases | Health |
Individuals who remain HBsAg positive for at least six months are considered to be carriers. Carriers of the virus may have chronic hepatitis B, which would be reflected by elevated serum alanine aminotransferase (ALT) levels and inflammation of the liver, if they are in the immune clearance phase of chronic infection. Carriers who have seroconverted to HBeAg negative status, in particular those who acquired the infection as adults, have very little viral multiplication and hence may be at little risk of long-term complications or of transmitting infection to others. However, it is possible for individuals to enter an "immune escape" with HBeAg-negative hepatitis.
PCR tests have been developed to detect and measure the amount of HBV DNA, called the viral load, in clinical specimens. These tests are used to assess a person's infection status and to monitor treatment. Individuals with high viral loads, characteristically have ground glass hepatocytes on biopsy.
Prevention
Vaccine
Vaccines for the prevention of hepatitis B have been routinely recommended for babies since 1991 in the United States. The first dose is generally recommended within a day of birth. The hepatitis B vaccine was the first vaccine capable of preventing cancer, specifically liver cancer.
Most vaccines are given in three doses over a course of days. A protective response to the vaccine is defined as an anti-HBs antibody concentration of at least 10 mIU/ml in the recipient's serum. The vaccine is more effective in children and 95 percent of those vaccinated have protective levels of antibody. This drops to around 90% at 40 years of age and to around 75 percent in those over 60 years. The protection afforded by vaccination is long lasting even after antibody levels fall below 10 mIU/ml. For newborns of HBsAg-positive mothers: hepatitis B vaccine alone, hepatitis B immunoglobulin alone, or the combination of vaccine plus hepatitis B immunoglobulin, all prevent hepatitis B occurrence. Furthermore, the combination of vaccine plus hepatitis B immunoglobulin is superior to vaccine alone. This combination prevents HBV transmission around the time of birth in 86% to 99% of cases. | Hepatitis B | Wikipedia | 446 | 15925628 | https://en.wikipedia.org/wiki/Hepatitis%20B | Biology and health sciences | Viral diseases | Health |
Tenofovir given in the second or third trimester can reduce the risk of mother to child transmission by 77% when combined with hepatitis B immunoglobulin and the hepatitis B vaccine, especially for pregnant women with high hepatitis B virus DNA levels. However, there is not sufficient evidence that the administration of hepatitis B immunoglobulin alone during pregnancy, might reduce transmission rates to the newborn infant. No randomized control trial has been conducted to assess the effects of hepatitis B vaccine during pregnancy for preventing infant infection.
All those with a risk of exposure to body fluids such as blood should be vaccinated, if not already. Testing to verify effective immunization is recommended and further doses of vaccine are given to those who are not sufficiently immunized.
In 10- to 22-year follow-up studies there were no cases of hepatitis B among those with a normal immune system who were vaccinated. Only rare chronic infections have been documented. Vaccination is particularly recommended for high risk groups including: health workers, people with chronic kidney failure, and men who have sex with men.
Both types of the hepatitis B vaccine, the plasma-derived vaccine (PDV) and the recombinant vaccine (RV) are of similar effectiveness in preventing infection in both healthcare workers and chronic kidney failure groups. One difference was noticed among the health worker group: the RV intramuscular route was significantly more effective compared with the RV intradermal route of administration.
Other
In assisted reproductive technology, sperm washing is not necessary for males with hepatitis B to prevent transmission, unless the female partner has not been effectively vaccinated. In females with hepatitis B, the risk of transmission from mother to child with IVF is no different from the risk in spontaneous conception.
Those at high risk of infection should be tested as there is effective treatment for those who have the disease. Groups that screening is recommended for include those who have not been vaccinated and one of the following: people from areas of the world where hepatitis B occurs in more than 2%, those with HIV, intravenous drug users, men who have sex with men, and those who live with someone with hepatitis B. Screening during pregnancy is recommended in the United States.
Treatment | Hepatitis B | Wikipedia | 455 | 15925628 | https://en.wikipedia.org/wiki/Hepatitis%20B | Biology and health sciences | Viral diseases | Health |
Acute infection does not usually require treatment and most adults clear the infection spontaneously. Early antiviral treatment may be required in fewer than 1% of people, whose infection takes a very aggressive course (fulminant hepatitis) or who are immunocompromised. On the other hand, treatment of chronic infection may be necessary to reduce the risk of cirrhosis and liver cancer. Chronically infected individuals with persistently elevated serum alanine aminotransferase, a marker of liver damage, and HBV DNA levels are candidates for therapy. Treatment lasts from six months to a year, depending on medication and genotype. Treatment duration when medication is taken by mouth, however, is more variable and usually longer than one year.
Although none of the available medications can clear the infection, they can stop the virus from replicating, thus minimizing liver damage. As of 2024, there are seven medications licensed for the treatment of infection in the United States. These include antiviral medications lamivudine, adefovir, tenofovir disoproxil, tenofovir alafenamide, telbivudine, and entecavir, and the two immune system modulators interferon alpha-2a and PEGylated interferon alpha-2a. In 2015, the World Health Organization recommended tenofovir or entecavir as first-line agents. Those with current cirrhosis are in most need of treatment.
The use of interferon, which requires injections daily or thrice weekly, has been supplanted by long-acting PEGylated interferon, which is injected only once weekly. However, some individuals are much more likely to respond than others, and this might be because of the genotype of the infecting virus or the person's heredity. The treatment reduces viral replication in the liver, thereby reducing the viral load (the amount of virus particles as measured in the blood). Response to treatment differs between the genotypes. Interferon treatment may produce an e antigen seroconversion rate of 37% in genotype A but only a 6% seroconversion in type D. Genotype B has similar seroconversion rates to type A while type C seroconverts only in 15% of cases. Sustained e antigen loss after treatment is ~45% in types A and B but only 25–30% in types C and D. | Hepatitis B | Wikipedia | 507 | 15925628 | https://en.wikipedia.org/wiki/Hepatitis%20B | Biology and health sciences | Viral diseases | Health |
It seems unlikely that the disease will be eliminated by 2030, the goal set in 2016 by WHO. However, progress is being made in developing therapeutic treatments. In 2010, the Hepatitis B Foundation reported that 3 preclinical and 11 clinical-stage drugs were under development, based on largely similar mechanisms. In 2020, they reported that there were 17 preclinical- and 32 clinical-stage drugs under development, using diverse mechanisms.
Prognosis
virus infection may be either acute (self-limiting) or chronic (long-standing). Persons with self-limiting infection clear the infection spontaneously within weeks to months.
Children are less likely than adults to clear the infection. More than 95% of people who become infected as adults or older children will stage a full recovery and develop protective immunity to the virus. However, this drops to 30% for younger children, and only 5% of newborns that acquire the infection from their mother at birth will clear the infection. This population has a 40% lifetime risk of death from cirrhosis or hepatocellular carcinoma. Of those infected between the age of one to six, 70% will clear the infection.
Hepatitis D (HDV) can occur only with a concomitant infection, because HDV uses the HBV surface antigen to form a capsid. Co-infection with hepatitis D increases the risk of liver cirrhosis and liver cancer. Polyarteritis nodosa is more common in people with infection.
Cirrhosis
A number of different tests are available to determine the degree of cirrhosis present. Transient elastography (FibroScan) is the test of choice, but it is expensive. Aspartate aminotransferase to platelet ratio index may be used when cost is an issue. | Hepatitis B | Wikipedia | 364 | 15925628 | https://en.wikipedia.org/wiki/Hepatitis%20B | Biology and health sciences | Viral diseases | Health |
Reactivation
virus DNA remains in the body after infection, and in some people, including those that do not have detectable HBsAg, the disease recurs. Although rare, reactivation is seen most often following alcohol or drug use, or in people with impaired immunity. HBV goes through cycles of replication and non-replication. Approximately 50% of overt carriers experience acute reactivation. Males with baseline ALT of 200 UL/L are three times more likely to develop a reactivation than people with lower levels. Although reactivation can occur spontaneously, people who undergo chemotherapy have a higher risk. Immunosuppressive drugs favor increased HBV replication while inhibiting cytotoxic T cell function in the liver. The risk of reactivation varies depending on the serological profile; those with detectable HBsAg in their blood are at the greatest risk, but those with only antibodies to the core antigen are also at risk. The presence of antibodies to the surface antigen, which are considered to be a marker of immunity, does not preclude reactivation. Treatment with prophylactic antiviral drugs can prevent the serious morbidity associated with HBV disease reactivation.
Epidemiology
Approximately 254 million people had chronic HBV infection as of 2022. Another 1.2 million cases of acute HBV infection also occurred that year. Regional prevalences across the globe range from around 7.5% in Africa to 0.5% in the Americas.
The primary method of HBV transmission and the prevalence of chronic HBV infection in specific regions often correspond with one another. In populations where HBV infection rates are 8% or higher, which are classified as high prevalence, vertical transmission (usually occurring during birth) is most common, though rates of early childhood transmission can also be significant among these populations. In 2021, 19 African countries had infection rates ranging between 8-19%, placing them in the high prevalence category. High prevalence of HBV also exists in Mongolia.
In moderate prevalence areas where 2–7% of the population is chronically infected, the disease is predominantly spread horizontally, often among children, but also vertically. China's HBV infection rate is at the higher end of the moderate prevalence classification with an infection rate of 6.89% as of 2019. HBV prevalence in India is also moderate, with studies placing India's infection rate between 2-4%. | Hepatitis B | Wikipedia | 498 | 15925628 | https://en.wikipedia.org/wiki/Hepatitis%20B | Biology and health sciences | Viral diseases | Health |
Countries with low HBV prevalence include Australia (0.9%), those in the WHO European Region (which average 1.5%), and most countries in North and South America (which average 0.28%).
In the United States, an estimated 0.26% of the population was living with HBV infection as of 2018.
History
Findings of HBV DNA in ancient human remains have shown that HBV has infected humans for at least ten millennia, both in Eurasia and in the Americas. This disproved the belief that hepatitis B originated in the New World and spread to Europe around 16th century. Hepatitis B virus subgenotype C4 is exclusively present in Australian aborigines, suggesting an ancient origin as much as 50,000 years old. However, analyses of ancient HBV genomes suggested that the most recent common ancestor of all known human HBV strains was dated to between 20,000 and 12,000 years ago, pointing to a more recent origin for all HBV genotypes. The evolution of HBV in humans was shown to reflect known events of human history such as the first peopling of the Americas during the late Pleistocene and the Neolithic transition in Europe. Ancient DNA studies have also showed that some ancient hepatitis viral strains still infect humans, while other strains became extinct.
The earliest record of an epidemic caused by virus was made by Lurman in 1885. An outbreak of smallpox occurred in Bremen in 1883 and 1,289 shipyard employees were vaccinated with lymph from other people. After several weeks, and up to eight months later, 191 of the vaccinated workers became ill with jaundice and were diagnosed with serum hepatitis. Other employees who had been inoculated with different batches of lymph remained healthy. Lurman's paper, now regarded as a classical example of an epidemiological study, proved that contaminated lymph was the source of the outbreak. Later, numerous similar outbreaks were reported following the introduction, in 1909, of hypodermic needles that were used, and, more importantly, reused, for administering Salvarsan for the treatment of syphilis.
The largest recorded outbreak of hepatitis B was the infection of up to 330,000 American soldiers during World War II. The outbreak has been blamed on a yellow fever vaccine made with contaminated human blood serum, and after receiving the vaccinations about 50,000 soldiers developed jaundice. | Hepatitis B | Wikipedia | 506 | 15925628 | https://en.wikipedia.org/wiki/Hepatitis%20B | Biology and health sciences | Viral diseases | Health |
The virus was not discovered until 1966 when Baruch Blumberg, then working at the National Institutes of Health (NIH), discovered the Australia antigen (later known to be surface antigen, or HBsAg) in the blood of Aboriginal Australian people. Although a virus had been suspected since the research published by Frederick MacCallum in 1947, David Dane and others discovered the virus particle in 1970 by electron microscopy. In 1971, the FDA issued its first-ever blood supply screening order to blood banks. By the early 1980s the genome of the virus had been sequenced, and the first vaccines were being tested.
Society and culture
World Hepatitis Day, observed 28 July, aims to raise global awareness of and hepatitis C and encourage prevention, diagnosis, and treatment. It has been led by the World Hepatitis Alliance since 2007 and in May 2010, it received global endorsement from the World Health Organization. | Hepatitis B | Wikipedia | 178 | 15925628 | https://en.wikipedia.org/wiki/Hepatitis%20B | Biology and health sciences | Viral diseases | Health |
Pig farming, pork farming, or hog farming is the raising and breeding of domestic pigs as livestock, and is a branch of animal husbandry. Pigs are farmed principally for food (e.g. pork: bacon, ham, gammon) and skins.
Pigs are amenable to many different styles of farming: intensive commercial units, commercial free range enterprises, or extensive farming (being allowed to wander around a village, town or city, or tethered in a simple shelter or kept in a pen outside the owner's house). Historically, farm pigs were kept in small numbers and were closely associated with the residence of the owner, or in the same village or town. They were valued as a source of meat and fat, and for their ability to convert inedible food into meat and manure, and were often fed household food waste when kept on a homestead. Pigs have been farmed to dispose of municipal garbage on a large scale.
All these forms of pig farm are in use today, though intensive farms are by far the most popular, due to their potential to raise a large amount of pigs in a very cost-efficient manner. In developed nations, commercial farms house thousands of pigs in climate-controlled buildings. Pigs are a popular form of livestock, with more than one billion pigs butchered each year worldwide, 100 million in the United States. The majority of pigs are used for human food, but also supply skin, fat and other materials for use in clothing, ingredients for processed foods, cosmetics, and medical use.
Production and trade | Pig farming | Wikipedia | 315 | 15929223 | https://en.wikipedia.org/wiki/Pig%20farming | Technology | Animal husbandry | null |
Pigs are farmed in many countries, though the countries mainly consuming them are in Asia, meaning there is a significant international and even intercontinental trade in live and slaughtered pigs. Despite having the world's largest herd, China is a net importer of pigs as China consumes about 50% of global pork production. The total amount of pork consumed in China is 57 million tons (as of 2021) and pork accounted for 60 percent of total meat consumption within the country. China has been increasing its imports during its economic development; many within China's population of 1.2 billion people prioritize eating pork as their main consumption of meat, unlike other countries where most people would prioritize having poultry. In addition, since 2007, China possesses a strategic pork reserve with a government mandate to "stabilize live hog prices, prevent excessive hog price drops, which damage the interests of farmers and to ease the negative effects of the cyclical nature of hog production and market prices." In China, the government actively intervened in the pork market during periods of instability by releasing pork reserves into the market whenever hogs get too expensive in China, in order to hold down prices for consumers. Conversely when prices of pork are deemed too low and unsustainable for farmers, the reserve buys up pigs to ensure farmers remain profitable.
The largest exporters of pigs are the United States, the European Union, and Canada. As an example, more than half of Canadian production (22.8 million pigs) in 2008 was exported, going to 143 countries.
Among animals raised for their meat, pigs have a lower feed conversion ratio than cattle, which can provide an advantage in lower unit price of meat because the cost of animal feed per kilogram or pound of resultant meat is lower. However, there are also many other economic variables in meat production and distribution, so the price differential of pork and beef at the point of retail sale does not always correspond closely to the differential in feed conversion ratios. Nonetheless, the favorable ratio often tends to make pork more affordable compared to beef.
Relationship between handlers and pigs
The way in which a stockperson interacts with pigs affects animal welfare which in some circumstances can correlate with production measures. Many routine interactions can cause fear, which can result in stress and decreased production.
There are various methods of handling pigs which can be separated into those which lead to positive or negative reactions by the animals. These reactions are based on how the pigs interpret a handler's behavior. | Pig farming | Wikipedia | 499 | 15929223 | https://en.wikipedia.org/wiki/Pig%20farming | Technology | Animal husbandry | null |
Negative interactions
Many negative interactions with pigs arise from stock-people dealing with large numbers of pigs. Because of this, many handlers can become complacent about animal welfare and fail to ensure positive interactions with pigs. Negative interactions include overly heavy tactile interactions (slaps, punches, kicks, and bites), the use of electric goads and fast movements. It can also include killing them. However, it is not a commonly held view that death is a negative interaction. These interactions can result in fear in the animals, which can develop into stress. Overly heavy tactile interactions from the human handlers can cause increased basal cortisol levels (a "stress" hormone). Negative interactions that cause fear mean the escape reactions of the pigs can be extremely vigorous, thereby risking injury to both stock and handlers. Stress can result in immunosuppression, leading to an increased susceptibility to disease. Studies have shown that these negative handling techniques result in an overall reduction in growth rates of pigs.
"In Canada the Federal government does not regulate the treatment on farms and most provinces have animal cruelty legislation but they typically contain expectations for general agricultural practices." Due to this lack of legislation, this perpetuates to the cruel treatment of swine. "The NFACC codes of practice are developed larger by the industry and are not enforced with third party oversight."
Positive interactions
Various interactions can be considered either positive or neutral. Neutral interactions are considered positive because, in conjunction with positive interactions, they contribute to an overall non-negative relationship between the pig handler and the animal livestock. Pigs are often fearful of fast movements. When entering a pen, it is good practice for the pig handler to enter with slow and deliberate movements. These minimize fear and therefore reduce stress. Pigs are very curious animals. Allowing the pigs to approach and smell whilst patting or resting a hand on the pig's back are examples of positive behavior. Pigs also respond positively to verbal interaction. Minimizing fear of humans allow handlers to perform husbandry practices in a safer and more efficient manner. By reducing stress, stock are made more comfortable to feed when near the pig handlers, resulting in increased productivity.
Impacts on sow breeding
Hogs raised in confinement systems tend to produce 23.5 piglets per year. Between 2013 and 2016, sow death rates nearly doubled in the United States, from 5.8 to 10.2 percent. 25 to 50 percent of deaths were caused by prolapse. | Pig farming | Wikipedia | 509 | 15929223 | https://en.wikipedia.org/wiki/Pig%20farming | Technology | Animal husbandry | null |
Other probable causes of death include vitamin deficiency, mycotoxins in feed, high density diets or abdominal issues. Iowa's Pork Industry Center collects mortality data in collaboration with the National Pork Board to collect data from over 400,000 sows from 16 U.S. states. The farms range in size and facility types. Increasing death rates are a profit concern to the industry, so money is invested into research to find solutions.
Genetic manipulation
Pigs were originally bred to rapidly gain weight and backfat in the late 1980s. In a more fat-conscious modern day America, pigs are now being bred to have less back fat and produce more offspring, which pushes the sow's body too far and is deemed one of the causes of the current prolapse epidemic. Researchers and veterinarians are seeking ways to positively impact the health of the hogs and benefit the hog business without taking much from the economy.
Terminology
Pigs are extensively farmed, and therefore the terminology is well developed:
Pig, hog, or swine, the species as a whole, or any member of it. The singular of "swine" is the same as the plural.
Shoat (or shote), piglet, or (where the species is called "hog") pig, unweaned young pig, or any immature pig
Sucker, a pig between birth and weaning
Weaner, a young pig recently separated from the sow
Runt, an unusually small and weak piglet, often one in a litter
Boar or hog, male pig of breeding age
Barrow, male pig castrated before puberty
Stag, male pig castrated later in life (castrated after maturity)
Gilt, young female not yet mated, or not yet farrowed, or after only one litter (depending on local usage).
Sow, breeding female, or female after first or second litter
Pigs for slaughter | Pig farming | Wikipedia | 386 | 15929223 | https://en.wikipedia.org/wiki/Pig%20farming | Technology | Animal husbandry | null |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.