Asymmetry

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Asymmetry

Asymmetrical fire barrier, required by ASTM E119 to be fire tested on both sides. The lowest result achieved equates to the overall fire-resistance rating of the system in order to ensure that the barrier works equally well from both sides.

 

Asymmetry is the absence of, or a violation of, symmetry (the property of an object being invariant to a transformation, such as reflection). Symmetry is an important property of both physical and abstract systems and it may be displayed in precise terms or in more aesthetic terms. The absence of or violation of symmetry that are either expected or desired can have important consequences for a system.

In organisms

Due to how cells divide in organisms, asymmetry in organisms is fairly usual in at least one dimension, with biological symmetry also being common in at least one dimension. 

Louis Pasteur proposed that biological molecules are asymmetric because the cosmic [i.e. physical] forces that preside over their formation are themselves asymmetric. While at his time, and even now, the symmetry of physical processes are highlighted, it is known that there are fundamental physical asymmetries, starting with time. 

Asymmetry in biology

Asymmetry is an important and widespread trait, having evolved numerous times in many organisms and at many levels of organisation (ranging from individual cells, through organs, to entire body-shapes). Benefits of asymmetry sometimes have to do with improved spatial arrangements, such as the left human lung being smaller, and having one fewer lobes than the right lung to make room for the asymmetrical heart. In other examples, division of function between the right and left half may have been beneficial and has driven the asymmetry to become stronger. Such an explanation is usually given for mammal hand or paw preference (Handedness), an asymmetry in skill development in mammals. Training the neural pathways in a skill with one hand (or paw) may take less effort than doing the same with both hands.

Nature also provides several examples of handedness in traits that are usually symmetric. The following are examples of animals with obvious left-right asymmetries: 

Fiddler crab, Uca pugnax

• Most snails, because of torsion during development, show remarkable asymmetry in the shell and in the internal organs.
• Fiddler crabs have one big claw and one small claw.
• The narwhal's tusk is a left incisor which can grow up to 10 feet in length and forms a left-handed helix.
• Flatfish have evolved to swim with one side upward, and as a result have both eyes on one side of their heads.
• Several species of owls exhibit asymmetries in the size and positioning of their ears, which is thought to help locate prey.
• Many animals (ranging from insects to mammals) have asymmetric male genitalia. The evolutionary cause behind this is, in most cases, still a mystery.

As an indicator of unfitness

• Certain disturbances during the development of the organism, resulting in birth defects.
• Injuries after cell division that cannot be biologically repaired, such as a lost limb from an accident.

Since birth defects and injuries are likely to indicate poor health of the organism, defects resulting in asymmetry often put an animal at a disadvantage when it comes to finding a mate. In particular, a degree of facial symmetry is associated with physical attractiveness, but complete symmetry is both impossible and probably unattractive.

In structures

Pre-modern architectural styles tended to place an emphasis on symmetry, except where extreme site conditions or historical developments lead away from this classical ideal. To the contrary, modernist and postmodern architects became much more free to use asymmetry as a design element.

While most bridges employ a symmetrical form due to intrinsic simplicities of design, analysis and fabrication and economical use of materials, a number of modern bridges have deliberately departed from this, either in response to site-specific considerations or to create a dramatic design statement.

Some asymmetrical structures

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  Eastern span replacement of the San Francisco – Oakland Bay Bridge
  
  
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  Puente de la Mujer
  
  
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  Auditorio de Tenerife
  
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  Blohm & Voss BV 141 aircraft
  
  
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  A proa, a form of outrigger canoe
  
  

In fire protection

In fire-resistance rated wall assemblies, used in passive fire protection, including, but not limited to, high-voltage transformer fire barriers, asymmetry is a crucial aspect of design. When designing a facility, it is not always certain, that in the event of fire, which side a fire may come from. Therefore, many building codes and fire test standards outline, that a symmetrical assembly, need only be tested from one side, because both sides are the same. However, as soon as an assembly is asymmetrical, both sides must be tested and the test report is required to state the results for each side. In practical use, the lowest result achieved is the one that turns up in certification listings. Neither the test sponsor, nor the laboratory can go by an opinion or deduction as to which side was in more peril as a result of contemplated testing and then test only one side. Both must be tested in order to be compliant with test standards and building codes.

 

In mathematics

There are no a and b such that a < b and b < a. This form of asymmetry is an asymmetrical relation.

In chemistry

Certain molecules are chiral; that is, they cannot be superposed upon their mirror image. Chemically identical molecules with different chirality are called enantiomers; this difference in orientation can lead to different properties in the way they react with biological systems. 

In physics

Asymmetry arises in physics in a number of different realms. 

Thermodynamics

The original non-statistical formulation of thermodynamics was asymmetrical in time: it claimed that the entropy in a closed system can only increase with time. This was derived from the Second Law (any of the two, Clausius' or Lord Kelvin's statement can be used since they are equivalent) and using the Clausius' Theorem (see Kerson Huang ISBN 978-0471815181). The later theory of statistical mechanics, however, is symmetric in time. Although it states that a system significantly below maximum entropy is very likely to evolve towards higher entropy, it also states that such a system is very likely to have evolved from higher entropy. 

Particle physics

Symmetry is one of the most powerful tools in particle physics, because it has become evident that practically all laws of nature originate in symmetries. Violations of symmetry therefore present theoretical and experimental puzzles that lead to a deeper understanding of nature. Asymmetries in experimental measurements also provide powerful handles that are often relatively free from background or systematic uncertainties.

Parity violation

Until the 1950s, it was believed that fundamental physics was left-right symmetric; i.e., that interactions were invariant under parity. Although parity is conserved in electromagnetism, strong interactions and gravity, it turns out to be violated in weak interactions. The Standard Model incorporates parity violation by expressing the weak interaction as a chiral gauge interaction. Only the left-handed components of particles and right-handed components of antiparticles participate in weak interactions in the Standard Model. A consequence of parity violation in particle physics is that neutrinos have only been observed as left-handed particles (and antineutrinos as right-handed particles). 

In 1956-1957 Chien-Shiung Wu, E. Ambler, R. W. Hayward, D. D. Hoppes, and R. P. Hudson found a clear violation of parity conservation in the beta decay of cobalt-60. Simultaneously, R. L. Garwin, Leon Lederman, and R. Weinrich modified an existing cyclotron experiment and immediately verified parity violation.

CP violation

After the discovery of the violation of parity in 1956-57, it was believed that the combined symmetry of parity (P) and simultaneous charge conjugation (C), called CP, was preserved. For example, CP transforms a left-handed neutrino into a right-handed antineutrino. In 1964, however, James Cronin and Val Fitch provided clear evidence that CP symmetry was also violated in an experiment with neutral kaons. 

CP violation is one of the necessary conditions for the generation of a baryon asymmetry in the universe.

Combining the CP symmetry with simultaneous time reversal (T) produces a combined symmetry called CPT symmetry. CPT symmetry must be preserved in any Lorentz invariant local quantum field theory with a Hermitian Hamiltonian. As of 2006, no violations of CPT symmetry have been observed.

Baryon asymmetry of the universe

The baryons (i.e., the protons and neutrons and the atoms that they comprise) observed so far in the universe are overwhelmingly matter as opposed to anti-matter. This asymmetry is called the baryon asymmetry of the universe.

Isospin violation

Isospin is the symmetry transformation of the weak interactions. The concept was first introduced by Werner Heisenberg in nuclear physics based on the observations that the masses of the neutron and the proton are almost identical and that the strength of the strong interaction between any pair of nucleons is the same, independent of whether they are protons or neutrons. This symmetry arises at a more fundamental level as a symmetry between up-type and down-type quarks. Isospin symmetry in the strong interactions can be considered as a subset of a larger flavor symmetry group, in which the strong interactions are invariant under interchange of different types of quarks. Including the strange quark in this scheme gives rise to the Eightfold Way scheme for classifying mesons and baryons.

Isospin is violated by the fact that the masses of the up and down quarks are different, as well as by their different electric charges. Because this violation is only a small effect in most processes that involve the strong interactions, isospin symmetry remains a useful calculational tool, and its violation introduces corrections to the isospin-symmetric results. 

In collider experiments

Because the weak interactions violate parity, collider processes that can involve the weak interactions typically exhibit asymmetries in the distributions of the final-state particles. These asymmetries are typically sensitive to the difference in the interaction between particles and antiparticles, or between left-handed and right-handed particles. They can thus be used as a sensitive measurement of differences in interaction strength and/or to distinguish a small asymmetric signal from a large but symmetric background.

• A forward-backward asymmetry is defined as A_FB=(N_F-N_B)/(N_F+N_B), where N_F is the number of events in which some particular final-state particle is moving "forward" with respect to some chosen direction (e.g., a final-state electron moving in the same direction as the initial-state electron beam in electron-positron collisions), while N_B is the number of events with the final-state particle moving "backward". Forward-backward asymmetries were used by the LEP experiments to measure the difference in the interaction strength of the Z boson between left-handed and right-handed fermions, which provides a precision measurement of the weak mixing angle.
• A left-right asymmetry is defined as A_LR=(N_L-N_R)/(N_L+N_R), where N_L is the number of events in which some initial- or final-state particle is left-polarized, while N_R is the corresponding number of right-polarized events. Left-right asymmetries in Z boson production and decay were measured at the Stanford Linear Collider using the event rates obtained with left-polarized versus right-polarized initial electron beams. Left-right asymmetries can also be defined as asymmetries in the polarization of final-state particles whose polarizations can be measured; e.g., tau leptons.
• A charge asymmetry or particle-antiparticle asymmetry is defined in a similar way. This type of asymmetry has been used to constrain the parton distribution functions of protons at the Tevatron from events in which a produced W boson decays to a charged lepton. The asymmetry between positively and negatively charged leptons as a function of the direction of the W boson relative to the proton beam provides information on the relative distributions of up and down quarks in the proton. Particle-antiparticle asymmetries are also used to extract measurements of CP violation from B meson and anti-B meson production at the BaBar and Belle experiments.

Lexical

Asymmetry is also relevant to grammar and linguistics, especially in the contexts of lexical analysis and transformational grammar.

Enumeration example: In English, there are grammatical rules for specifying coordinate items in an enumeration or series. Similar rules exist for programming languages and mathematical notation. These rules vary, and some require lexical asymmetry to be considered grammatically correct.

For example, in standard written English: 

   We sell domesticated cats, dogs, and goldfish.        ### in-line asymmetric and grammatical
   We sell domesticated animals (cats, dogs, goldfish).  ### in-line symmetric and grammatical
   We sell domesticated animals (cats, dogs, goldfish,). ### in-line symmetric and ungrammatical
   We sell domesticated animals:                         ### outline symmetric and grammatical
     - cats
     - dogs
     - goldfish

Chirality

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Chirality 

 

Two enantiomers of a generic amino acid that is chiral

Chirality /kaɪˈrælɪtiː/ is a property of asymmetry important in several branches of science. The word chirality is derived from the Greek χειρ (kheir), "hand," a familiar chiral object.

An object or a system is chiral if it is distinguishable from its mirror image; that is, it cannot be superposed onto it. Conversely, a mirror image of an achiral object, such as a sphere, cannot be distinguished from the object. A chiral object and its mirror image are called enantiomorphs (Greek, "opposite forms") or, when referring to molecules, enantiomers. A non-chiral object is called achiral (sometimes also amphichiral) and can be superposed on its mirror image.

The term was first used by Lord Kelvin in 1893 in the second Robert Boyle Lecture at the Oxford University Junior Scientific Club which was published in 1894:

I call any geometrical figure, or group of points, 'chiral', and say that it has chirality if its image in a plane mirror, ideally realized, cannot be brought to coincide with itself.

Human hands are perhaps the most universally recognized example of chirality. The left hand is a non-superimposable mirror image of the right hand; no matter how the two hands are oriented, it is impossible for all the major features of both hands to coincide across all axes. This difference in symmetry becomes obvious if someone attempts to shake the right hand of a person using their left hand, or if a left-handed glove is placed on a right hand. In mathematics, chirality is the property of a figure that is not identical to its mirror image.

Mathematics

An achiral 3D object without central symmetry or a plane of symmetry

 

A table of all prime knots with seven crossings or fewer (not including mirror images).

In mathematics, a figure is chiral (and said to have chirality) if it cannot be mapped to its mirror image by rotations and translations alone. For example, a right shoe is different from a left shoe, and clockwise is different from anticlockwise.

A chiral object and its mirror image are said to be enantiomorphs. The word enantiomorph stems from the Greek ἐναντίος (enantios) 'opposite' + μορφή (morphe) 'form'. A non-chiral figure is called achiral or amphichiral.

The helix (and by extension a spun string, a screw, a propeller, etc.) and Möbius strip are chiral two-dimensional objects in three-dimensional ambient space. The J, L, S and Z-shaped tetrominoes of the popular video game Tetris also exhibit chirality, but only in a two-dimensional space.

Many other familiar objects exhibit the same chiral symmetry of the human body, such as gloves, glasses (where two lenses differ in prescription), and shoes. A similar notion of chirality is considered in knot theory, as explained below. 

Some chiral three-dimensional objects, such as the helix, can be assigned a right or left handedness, according to the right-hand rule. 

Geometry

In geometry a figure is achiral if and only if its symmetry group contains at least one orientation-reversing isometry. In two dimensions, every figure that possesses an axis of symmetry is achiral, and it can be shown that every bounded achiral figure must have an axis of symmetry. In three dimensions, every figure that possesses a plane of symmetry or a center of symmetry is achiral. There are, however, achiral figures lacking both plane and center of symmetry. In terms of point groups, all chiral figures lack an improper axis of rotation (S_n). This means that they cannot contain a center of inversion (i) or a mirror plane (σ). Only figures with a point group designation of C₁, C_n, D_n, T, O, or I can be chiral. 

Knot theory

A knot is called achiral if it can be continuously deformed into its mirror image, otherwise it is called chiral. For example, the unknot and the figure-eight knot are achiral, whereas the trefoil knot is chiral. 

Physics

Animation of left-handed (anticlockwise) circularly polarized light, as defined from the direction of the source in agreement with physics and astronomy conventions.

In physics, chirality may be found in the spin of a particle, where the handedness of the object is determined by the direction in which the particle spins. Not to be confused with helicity, which is the projection of the spin along the linear momentum of a subatomic particle, chirality is a purely quantum mechanical phenomenon like spin. Although both can have left-handed or right-handed properties, only in the massless case do they have a simple relation. In particular for a massless particle the helicity is the same as the chirality while for an antiparticle they have opposite sign. 

The handedness in both chirality and helicity relate to the rotation of a particle while it proceeds in linear motion with reference to the human hands. The thumb of the hand points towards the direction of linear motion whilst the fingers curl into the palm, representing the direction of rotation of the particle (i.e. clockwise and counterclockwise). Depending on the linear and rotational motion, the particle can either be defined by left-handedness or right-handedness. A symmetry transformation between the two is called parity. Invariance under parity by a Dirac fermion is called chiral symmetry. 

Electromagnetism

Electromagnetic wave propagation as handedness is wave polarization and described in terms of helicity (occurs as a helix). Polarization of an electromagnetic wave is the property that describes the orientation, i.e., the time-varying, direction (vector), and amplitude of the electric field vector. 

Chiral mirrors are a class of metamaterials that reflect circularly polarized light of a certain helicity in a handedness-preserving manner, while absorbing circular polarization of the opposite handedness. However, most absorbing chiral mirrors operate only in a narrow frequency band, as limited by the causality principle. Employing a different design methodology that allows undesired waves to pass through instead of absorbing the undesired waveform, chiral mirrors are able to show good performance in broadband.

Chemistry

(S)-Alanine (left) and (R)-alanine (right) in zwitterionic form at neutral pH

A chiral molecule is a type of molecule that has a non-superposable mirror image. The feature that is most often the cause of chirality in molecules is the presence of an asymmetric carbon atom.

The term "chiral" in general is used to describe the object that is non-superposable on its mirror image.

In chemistry, chirality usually refers to molecules. Two mirror images of a chiral molecule are called enantiomers or optical isomers. Pairs of enantiomers are often designated as "right-", "left-handed" or, if they have no bias, "achiral". As polarized light passes through a chiral molecule, the plane of polarization, when viewed along the axis toward the source, will be rotated clockwise (to the right) or anticlockwise (to the left). A right handed rotation is dextrorotary (d); that to the left is levorotary (l). The d- and l-isomers are the same compound but are called enantiomers. An equimolar mixture of the two optical isomers will produce no net rotation of polarized light as it passes through. Left handed molecules have l- prefixed to their names; d- is prefixed to right handed molecules. 

Molecular chirality is of interest because of its application to stereochemistry in inorganic chemistry, organic chemistry, physical chemistry, biochemistry, and supramolecular chemistry. 

More recent developments in chiral chemistry include the development of chiral inorganic nanoparticles that may have the similar tetrahedral geometry as chiral centers associated with sp3 carbon atoms traditionally associated with chiral compounds, but at larger scale. Helical and other symmetries of chiral nanomaterials were also obtained.

Biology

All of the known life-forms show specific chiral properties in chemical structures as well as macroscopic anatomy, development and behavior. In any specific organism or evolutionarily related set thereof, individual compounds, organs, or behavior are found in the same single enantiomorphic form. Deviation (having the opposite form) could be found in a small number of chemical compounds, or certain organ or behavior but that variation strictly depends upon the genetic make up of the organism. From chemical level (molecular scale), biological systems show extreme stereospecificity in synthesis, uptake, sensing, metabolic processing. A living system usually deals with two enantiomers of the same compound in drastically different ways.

In biology, homochirality is a common property of amino acids and carbohydrates. The chiral protein-making amino acids, which are translated through the ribosome from genetic coding, occur in the L form. However, D-amino acids are also found in nature. The monosaccharides (carbohydrate-units) are commonly found in D-configuration. DNA double helix is chiral (as any kind of helix is chiral), and B-form of DNA shows a right-handed turn.

R-(+)-Limonene found in orange

 

S-(–)-Limonene found in lemon

 

Sometimes, when two enantiomers of a compound found in organisms, they significantly differ in their taste, smell and other biological actions. For example, (+)-limonene found in orange (causing its smell), and (–)-limonene found in lemons (causing its smell), show different smells due to different biochemical interactions at human nose. (+)-Carvone is responsible for the smell of caraway seed oil, whereas (–)-carvone is responsible for smell of spearmint oil.

(S)-(+)-Carvone occurs in caraway seed oil, and (R)-(-)-carvone occurs in spearmint

 

Dextropropoxyphene or Darvon, a painkiller

 

Levopropoxyphene or Novrad, an anticough agent

Also, for artificial compounds, including medicines, in case of chiral drugs, the two enantiomers sometimes show remarkable difference in effect of their biological actions. Darvon (dextropropoxyphene) is a painkiller, whereas its enantiomer, Novrad (levopropoxyphene) is an anti-cough agent. In case of penicillamine, the (S-isomer used in treatment of primary chronic arthritis, whereas the (R)-isomer has no therapeutic effect as well as being highly toxic. In some cases the less therapeutically active enantiomer can cause side effects. For example, (S-naproxen is an analgesic but the (R-isomer cause renal problems. The naturally occurring plant form of alpha-tocopherol (vitamin E) is RRR-α-tocopherol whereas the synthetic form (all-racemic vitamin E, or dl-tocopherol) is equal parts of the stereoisomers RRR, RRS, RSS, SSS, RSR, SRS, SRR and SSR with progressively decreasing biological equivalency, so that 1.36 mg of dl-tocopherol is considered equivalent to 1.0 mg of d-tocopherol.

A natural left-handed helix, made by a certain climber plant's tendril.

Macroscopic examples of chirality are found in the plant kingdom, the animal kingdom and all other groups of organism. A simple example is the coiling direction of any climber plant, which can grow to form either a left- or right-handed helix.

Shells of two different species of sea snail: on the left is the normally sinistral (left-handed) shell of Neptunea angulata, on the right is the normally dextral (right-handed) shell of Neptunea despecta

 

In anatomy, chirality is found in the imperfect mirror image symmetry of many kinds of animal bodies. Organisms such as gastropods exhibit chirality in their coiled shells, resulting in an asymmetrical appearance. Over 90% of gastropod species  have dextral (right-handed) shells in their coiling, but a small minority of species and genera are virtually always sinistral (left-handed). A very few species (for example Amphidromus perversus) show an equal mixture of dextral and sinistral individuals. 

In humans, chirality (also referred to as handedness or laterality) is an attribute of humans defined by their unequal distribution of fine motor skill between the left and right hands. An individual who is more dexterous with the right hand is called right-handed, and one who is more skilled with the left is said to be left-handed. Chirality is also seen in the study of facial asymmetry. 

In flatfish, the Summer flounder or fluke are left-eyed, while halibut are right-eyed.

Popular Culture

Chirality, chiral theory and even "knots" of a sort feature very heavily in the 2019 video game Death Stranding, by Hideo Kojima and Kojima Productions.

Tocotrienol

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Tocotrienol

 

General chemical structure of tocotrienols. alpha(α)-Tocotrienol: R1 = Me, R2 = Me, R3 = Me; beta(β)-Tocotrienol: R1 = Me, R2 = H, R3= Me; gamma(γ)-Tocotrienol: R1 = H, R2 = Me, R3= Me; delta(δ)-Tocotrienol: R1 = H, R2 = H, R3= Me

The vitamin E family comprise four tocotrienols (alpha, beta, gamma, delta) and four tocopherols (alpha, beta, gamma, delta). The critical chemical structural difference between tocotrienols and tocopherols is that tocotrienols have unsaturated isoprenoid side chains with three carbon-carbon double bonds versus saturated side chains for tocopherols (see Figure).

Tocotrienols are compounds naturally occurring at higher levels in some vegetable oils, including palm oil, rice bran oil, wheat germ, barley, saw palmetto, annatto, and certain other types of seeds, nuts and grains, and the oils derived from them.

Chemically, different analogues of vitamin E all show some activity as a chemical antioxidant, but do not all have the same vitamin E equivalence. Tocotrienols demonstrate activity depending on the type of antioxidant performance being measured. All tocotrienols have some physical antioxidant activity due to an ability to donate a hydrogen atom (a proton plus electron) from the hydroxyl group on the chromanol ring, to free radical and reactive oxygen species. Historically studies of tocotrienols account for less than 1% of all research into vitamin E. A scientific compilation of tocotrienol research, Tocotrienols: Vitamin E Beyond Tocopherols, was published in 2013.

Health effects

A number of health benefits of tocotrienols have been proposed, included decreased risk of heart disease and cancer. The Food and Nutrition Board of the Institute of Medicine of the United States National Academy of Sciences does not define a Recommended Dietary Allowance or Adequate Intake for tocotrienols.

Brain

A review of human studies in middle-aged and elderly stated "Evidence from prospective and case-control studies suggested that increased blood levels of tocotrienols were associated with favorable cognitive function outcomes." The review qualified this statement by noting that randomized, controlled clinical trials were needed to evaluate these observations.

Heart disease

Tocotrienols have been linked to improved markers of heart disease.

Diabetes

Animal models and observational studies in humans have shown potential benefit.

Side effects

Tocotrienols are generally well tolerated and without significant side effects.

History

The discovery of tocotrienols was first reported by Pennock and Whittle in 1964, describing the isolation of tocotrienols from rubber. The biological significance of tocotrienols was clearly delineated in the early 1980s, when its ability to lower cholesterol was first reported by Qureshi and Elson in the Journal of Medicinal Chemistry. During the 1990s, the anti-cancer properties of tocopherols and tocotrienols began to be delineated. The current commercial sources of tocotrienol are rice and palm. Other natural tocotrienol sources include rice bran oil, coconut oil, cocoa butter, barley, and wheat germ. Tocotrienols are safe and human studies show no adverse effects with consumption of 240 mg/day for 48 months. Tocotrienol rich fractions from rice, palm, or annatto, used in nutritional supplements, functional foods, and anti-aging cosmetics, are available in the market at 20%, 35%, 50%, and 70% total vitamin E content. 

Etymology

Tocotrienols are named by analogy to tocopherols (from Greek words meaning to bear a pregnancy; but with this word changed to include the chemical difference that tocotrienols are trienes, meaning that they share identical structure with the tocopherols except for the addition of the three double bonds to their side chains.

Comparison of tocotrienols and tocopherols

Tocotrienols have only a single chiral center, which exists at the 2' chromanol ring carbon, at the point where the isoprenoid tail joins the ring. The other two corresponding centers in the phytyl tail of the corresponding tocopherols do not exist as chiral centers for tocotrienols due to unsaturation (C-C double bonds) at these sites. Tocotrienols extracted from plants are always dextrorotatory stereoisomers, signified as d-tocotrienols. In theory, (levorotatory; l-tocotrienol) forms of tocotrienols could exist as well, which would have a 2S rather than 2R configuration at the molecules' single chiral center, but unlike synthetic, dl-alpha-tocopherol, the marketed tocotrienol dietary supplements are all d-tocotrienol extracts from palm or annatto oils.

Tocotrienol studies confirm anti-oxidation, anti-inflammatory potentials and suggest anti-cancer effects better than the common forms of tocopherol due to their chemical structure. Scientists have suggested tocotrienols are better antioxidants than tocopherols. It has been proposed that the unsaturated side-chain in tocotrienols causes them to penetrate tissues with saturated fatty layers more efficiently than tocopherol. Lipid ORAC values are highest for δ-tocotrienol. However that study also says: "Regarding α-tocopherol equivalent antioxidant capacity, no significant differences in the antioxidant activity of all vitamin E isoforms were found." 

Metabolism and bioavailability

The metabolism and thus the bioavailability of tocotrienols are not well understood and simply increasing the intake of tocotrienols might not increase tocotrienol levels in the body.

α-Tocopherol interference

Various studies have shown that alpha-tocopherol interferes with tocotrienol benefits. High levels of α-tocopherol increase cholesterol production. α-Tocopherol interference with tocotrienol absorption was described previously by Ikeda, who showed that α-tococopherol interfered with absorption of α-tocotrienol, but not γ-tocotrienol. Finally, α-tocopherol was shown to interfere with tocotrienols by increasing catabolism.

Sources

In nature, tocotrienols are present in many plants and fruits. The palm fruit (Elaeis guineensis) is particularly high in tocotrienols, primarily gamma-tocotrienol, alpha-tocotrienol and delta-tocotrienol. Other cultivated plants high in tocotrienols includes rice, wheat, barley, rye and oat. In annatto, tocotrienols are relatively abundant (only delta- and gamma-tocotrienol however) and it contains no tocopherols.

Research

Radiation countermeasures

Following exposure to gamma radiation, hematopoietic stem cells (HSCs) in the bone marrow, which are important for producing blood cells, rapidly undergo apoptosis (cell death). There are no known treatments for this acute effect of radiation. Two studies conducted by the U.S. Armed Forces Radiobiology Research Institute (AFRRI) found that treatment with γ-tocotrienol or δ-tocotrienol enhanced survival of hematopoietic stem cells, which are essential for renewing the body's supply of blood cells. Based on these successful results of studies in mice, γ-tocotrienol is being studied for its safety and efficacy as a radioprotective measure in nonhuman primates.

Columbia River Basalt Group

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Columbia_River_Basalt_Group

 

The Columbia River Basalt Group (including the Steen and Picture Gorge basalts) extends over portions of five states.

 

The Columbia River Basalt Group is the youngest, smallest and one of the best-preserved continental flood basalt province on Earth, covering over 210,000 km² (81,000 sq mi) mainly eastern Oregon and Washington, western Idaho, and part of northern Nevada. The basalt group includes the Steen and Picture Gorge basalt formations. 

Introduction

During the middle to late Miocene epoch, the Columbia River flood basalts engulfed about 163,700 km² (63,200 sq mi) of the Pacific Northwest, forming a large igneous province with an estimated volume of 174,300 km³ (41,800 cu mi). Eruptions were most vigorous 17–14 million years ago, when over 99 percent of the basalt was released. Less extensive eruptions continued 14–6 million years ago.

Erosion resulting from the Missoula Floods has extensively exposed these lava flows, laying bare many layers of the basalt flows at Wallula Gap, the lower Palouse River, the Columbia River Gorge and throughout the Channeled Scablands.

The Columbia River Basalt Group is thought to be a potential link to the Chilcotin Group in south-central British Columbia, Canada. The Latah Formation sediments of Washington and Idaho are interbedded with a number of the Columbia River Basalt Group flows, and outcrop across the region.

Absolute dates, subject to a statistical uncertainty, are determined through radiometric dating using isotope ratios such as ⁴⁰Ar/³⁹Ar dating, which can be used to identify the date of solidifying basalt. In the CRBG deposits ⁴⁰Ar, which is produced by ⁴⁰K decay, only accumulates after the melt solidifies.

Other flood basalts include the Deccan Traps (late Cretaceous period), that cover an area of 500,000 km² (200,000 sq mi) in west-central India; the Emeishan Traps (Permian), which cover more than 250,000 square kilometers in southwestern China; and Siberian Traps (late Permian) that cover 2 million km² (800,000 sq mi) in Russia. 

Formation of the Columbia River Basalt Group

Some time during a 10–15 million-year period, lava flow after lava flow poured out, eventually reaching a thickness of more than 1.8 km (5,900 ft). As the molten rock came to the surface, the Earth's crust gradually sank into the space left by the rising lava. This subsidence of the crust produced a large, slightly depressed lava plain now known as the Columbia Basin or Columbia River Plateau. The northwesterly advancing lava forced the ancient Columbia River into its present course. The lava, as it flowed over the area, first filled the stream valleys, forming dams that in turn caused impoundments or lakes. In these ancient lake beds are found fossil leaf impressions, petrified wood, fossil insects, and bones of vertebrate animals.

In the middle Miocene, 17 to 15 Ma, the Columbia Plateau and the Oregon Basin and Range of the Pacific Northwest were flooded with lava flows. Both flows are similar in both composition and age, and have been attributed to a common source, the Yellowstone hotspot. The ultimate cause of the volcanism is still up for debate, but the most widely accepted idea is that the mantle plume or upwelling (similar to that associated with present-day Hawaii) initiated the widespread and voluminous basaltic volcanism about 17 million years ago. As hot mantle plume materials rise and reach lower pressures, the hot materials melt and interact with the materials in the upper mantle, creating magma. Once that magma breaches the surface, it flows as lava and then solidifies into basalt.

Transition to flood volcanism

In the Palouse River Canyon just downstream of Palouse Falls, the Sentinel Bluffs flows of the Grand Ronde Formation can be seen on the bottom, covered by the Ginkgo Flow of the Wanapum Basalt.

Prior to 17.5 million years ago, the Western Cascade Stratovolcanoes erupted with periodic regularity for over 20 million years, even as they do today. An abrupt transition to shield volcanic flooding took place in the mid-Miocene. The flows can be divided into four major categories: The Steens Basalt, Grande Ronde Basalt, the Wanapum Basalt, and the Saddle Mountains Basalt. The various lava flows have been dated by radiometric dating—particularly through measurement of the ratios of isotopes of potassium to argon. The Columbia River flood basalt province comprises more than 300 individual basalt lava flows that have an average volume of 500 to 600 cubic kilometres (120 to 140 cu mi).

Cause of the volcanism

Major hot-spots have often been tracked back to flood-basalt events. In this case the Yellowstone hotspot's initial flood-basalt event occurred near Steens Mountain when the Imnaha and Steens eruptions began. As the North American Plate moved several centimeters per year westward, the eruptions progressed through the Snake River Plain across Idaho and into Wyoming. Consistent with the hot spot hypothesis, the lava flows are progressively younger as one proceeds east along this path.

There is additional confirmation that Yellowstone is associated with a deep hot spot. Using tomographic images based on seismic waves, relatively narrow, deeply seated, active convective plumes have been detected under Yellowstone and several other hot spots. These plumes are much more focused than the upwelling observed with large-scale plate-tectonics circulation.

Location of Yellowstone Hotspot in millions of Years Ago

 

CRB-Yellowstone mantle plume model

 

The hot spot hypothesis is not universally accepted as it has not resolved several questions. The Yellowstone hot spot volcanism track shows a large apparent bow in the hot-spot track that does not correspond to changes in plate motion if the northern CRBG floods are considered. Further, the Yellowstone images show necking of the plume at 650 km (400 mi) and 400 km (250 mi), which may correspond to phase changes or may reflect still-to-be-understood viscosity effects. Additional data collection and further modeling will be required to achieve a consensus on the actual mechanism.

Speed of flood basalt emplacement

Yaquina Head Lighthouse sits atop erosion-resistant Ginkgo flow basalt over 500 km (310 mi) from its origin.

 

The Columbia River Basalt Group flows exhibit essentially uniform chemical properties through the bulk of individual flows, suggesting rapid placement. Ho and Cashman (1997) characterized the 500 km (310 mi)-long Ginkgo flow of the Columbia River Basalt Group, determining that it had been formed in roughly a week, based on the measured melting temperature along the flow from the origin to the most distant point of the flow, combined with hydraulics considerations. The Ginkgo basalt was examined over its 500 km (310 mi) flow path from a Ginkgo flow feeder dike near Kahlotus, Washington to the flow terminus in the Pacific Ocean at Yaquina Head, Oregon. The basalt had an upper melting temperature of 1095 ± 5 °C and a lower temperature to 1085 ± 5 °C; this indicates that the maximum temperature drop along the Ginkgo flow was 20 °C. The lava must have spread quickly to achieve this uniformity. Analyses indicate that the flow must remain laminar, as turbulent flow would cool more quickly. This could be accomplished by sheet flow, which can travel at velocities of 1 to 8 metres per second (2.2 to 17.9 mph) without turbulence and minimal cooling, suggesting that the Ginkgo flow occurred in less than a week. The cooling/hydraulics analyses are supported by an independent indicator; if longer periods were required, external water from temporarily dammed rivers would intrude, resulting in both more dramatic cooling rates and increased volumes of pillow lava. Ho's analysis is consistent with the analysis by Reidel et al. (1994), who proposed a maximum Pomona flow emplacement duration of several months based on the time required for rivers to be reestablished in their canyons following a basalt flow interruption.

Dating of the flood basalt flows

Looking south in Hole in the Ground Coulee, Washington. The upper basalt is a Priest Rapids Member flow lying above a Roza Member flow, while the lower canyon exposes a layer of Grand Ronde basalt.

 

Three major tools are used to date the CRBG flows: stratigraphy, radiometric dating, and magnetostratigraphy. These techniques have been key to correlating data from disparate basalt exposures and boring samples over five states.

Major eruptive pulses of flood basalt lavas are laid down stratigraphically. The layers can be distinguished by physical characteristics and chemical composition. Each distinct layer is typically assigned a name usually based on area (valley, mountain, or region) where that formation is exposed and available for study. Stratigraphy provides a relative ordering (ordinal ranking) of the CRBG layers.

Absolute dates, subject to a statistical uncertainty, are determined through radiometric dating using isotope ratios such as ⁴⁰Ar/³⁹Ar dating, which can be used to identify the date of solidifying basalt. In the CRBG deposits ⁴⁰Ar, which is produced by ⁴⁰K decay, only accumulates after the melt solidifies.

Parts of the Grande Ronde, Wanapum and Saddle Mountains basalts (in order from the bottom) are exposed at the Wallula Gap.

Magnetostratigraphy is also used to determine age. This technique uses the pattern of magnetic polarity zones of CRBG layers by comparison to the magnetic polarity timescale. The samples are analyzed to determine their characteristic remanent magnetization from the Earth's magnetic field at the time a stratum was deposited. This is possible as magnetic minerals precipitate in the melt (crystallize), they orient themselves with Earth's magnetic field.

The Steens Basalt captured a highly detailed record of the earth's magnetic reversal that occurred roughly 15 million years ago. Over a 10,000-year period, more than 130 flows solidified – roughly one flow every 75 years. As each flow cooled below about 500 °C (932 °F), it captured the magnetic field's orientation-normal, reversed, or in one of several intermediate positions. Most of the flows froze with a single magnetic orientation. However, several of the flows, which freeze from both the upper and lower surfaces, progressively toward the center, captured substantial variations in magnetic field direction as they froze. The observed change in direction was reported as 50⁰ over 15 days.

The major Columbia River Basalt Group flows

Steens Basalt

View from the top of Steens Mountain, looking out to Alvord Desert with basalt layers visible on the eroded face.

The Steens Basalt flows covered about 50,000 km² (19,000 sq mi) of the Oregon Plateau in sections up to 1 km (3,300 ft) thick. It contains the earliest identified eruption of the CRBG large igneous province. The type locality for the Steens basalt, which covers a large portion of the Oregon Plateau, is an approximately 1,000 m (3,300 ft) face of Steens Mountain showing multiple layers of basalt. The oldest of the flows considered part of the Columbia River Basalt Group, the Steens basalt, includes flows geographically separated but roughly concurrent with the Imnaha flows. Older Imnaha basalt north of Steens Mountain overlies the chemically distinct lowermost flows of Steens basalt; hence some flows of the Imnaha are stratigraphically younger than the lowermost Steens basalt.

One geomagnetic field reversal occurred during the Steens Basalt eruptions at approximately 16.7 Ma, as dated using ⁴⁰Ar/³⁹Ar ages and the geomagnetic polarity timescale. Steens Mountain and related sections of Oregon Plateau flood basalts at Catlow Peak and Poker Jim Ridge 70 to 90 km (43 to 56 mi) to the southeast and west of Steens Mountain, provide the most detailed magnetic field reversal data (reversed-to-normal polarity transition) yet reported in volcanic rocks.

Imnaha Basalt

The second oldest flows, the Imnaha Basalt, are exposed at the type locality: Imnaha, Oregon.

Virtually coeval with oldest of the flows, the Imnaha basalt flows welled up across northeastern Oregon. There were 26 major flows over the period, one roughly every 15,000 years. Although estimates are that this amounts to about 10% of the total flows, they have been buried under more recent flows, and are visible in few locations. They can be seen along the lower benches of the Imnaha River and Snake River in Wallowa county.

The Imnaha lavas have been dated using the K–Ar technique, and show a broad range of dates. The oldest is 17.67±0.32 Ma with younger lava flows ranging to 15.50±0.40 Ma. Although the Imnaha Basalt overlies Lower Steens Basalt, it has been suggested that it is interfingered with Upper Steens Basalt.

Grande Ronde Basalt

Saddle Mountains basalt dikes penetrating Grande Ronde basalts.

The next oldest of the flows, from 17 million to 15.6 million years ago, make up the Grande Ronde Basalt. Units (flow zones) within the Grande Ronde Basalt include the Meyer Ridge and the Sentinel Bluffs units. Geologists estimate that the Grande Ronde Basalt comprises about 85 percent of the total flow volume. It is characterized by a number of dikes called the Chief Joseph Dike Swarm near Joseph, Enterprise, Troy and Walla Walla through which the lava upwelling occurred (estimates range to up to 20,000 such dikes). Many of the dikes were fissures 5 to 10 m (16 to 33 ft) wide and up to 10 miles (16 km) in length, allowing for huge quantities of magma upwelling. Much of the lava flowed north into Washington as well as down the Columbia River channel to the Pacific Ocean; the tremendous flows created the Columbia River Plateau. The weight of this flow caused central Washington to sink, creating the broad Columbia Basin in Washington. The type locality for the formation is the canyon of the Grande Ronde River. Grande Ronde basalt flows and dikes can also be seen in the exposed 2,000-foot (610 m) walls of Joseph Canyon along Oregon Route 3.

The type locality for the Grande Ronde Basalt lies along the lower Grande Ronde as shown here.

The Grande Ronde basalt flows flooded down the ancestral Columbia River channel to the west of the Cascade Mountains. It can be found exposed along the Clackamas River and at Silver Falls State Park where the falls plunge over multiple layers of the Grande Ronde basalt. Evidence of eight flows can be found in the Tualatin Mountains on the west side of Portland.

Individual flows included large quantities of basalt. The McCoy Canyon flow of the Sentinel Bluffs Member released 4,278 km³ (1,026 cu mi) of basalt in layers of 10 to 60 m (33 to 197 ft) in thickness. The Umtanum flow has been estimated at about 2,750 km³ (660 cu mi) in layers 50 m (160 ft) deep. The Pruitt Draw flow of the Teepee Butte Member released about 2,350 km³ (560 cu mi) with layers of basalt up to 100 m (330 ft) thick.

Wanapum Basalt

Three Devil's grade in Moses Coulee, Washington. The upper basalt is Roza Member, while the lower canyon exposes Frenchman Springs Member basalt.

The Wanapum Basalt is made up of the Eckler Mountain Member (15.6 million years ago), the Frenchman Springs Member (15.5 million years ago), the Roza Member (14.9 million years ago) and the Priest Rapids Member (14.5 million years ago). They originated from vents between Pendleton, Oregon and Hanford, Washington.

The Frenchman Springs Member flowed along similar paths as the Grande Ronde basalts, but can be identified by different chemical characteristics. It flowed west to the Pacific, and can be found in the Columbia Gorge, along the upper Clackamas River, the hills south of Oregon City. and as far west as Yaquina Head near Newport, Oregon—a distance of 750 km (470 mi).

Saddle Mountains Basalt

The Saddle Mountains Basalt, seen prominently at the Saddle Mountains, is made up of the Umatilla Member flows, the Wilbur Creek Member flows, the Asotin Member flows (13 million years ago), the Weissenfels Ridge Member flows, the Esquatzel Member flows, the Elephant Mountain Member flows (10.5 million years ago), the Bujford Member flows, the Ice Harbor Member flows (8.5 million years ago) and the Lower Monumental Member flows (6 million years ago).

Related geologic structures

Oregon High Lava Plains

Level IV ecoregions in the Northern Basin and Range in Oregon, Idaho, Utah, and Nevada. The light brown region numbered 80g represent the High Lava Plains

Camp & Ross (2004) observed that the Oregon High Lava Plains is a complementary system of propagating rhyolite eruptions, with the same point of origin. The two phenomena occurred concurrently, with the High Lava Plains propagating westward since ~10 Ma, while the Snake River Plains propagated eastward.