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Hydrogen bond
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AFM image of napthalenetetracarboxylic diimide molecules on silver-terminated silicon, interacting via hydrogen bonding, taken at 77 K.[1] ("Hydrogen bonds" in the top image are exaggerated by artifacts of the imaging technique.[2][3])
Model of hydrogen bonds (1) between molecules of water
A hydrogen bond is the electrostatic attraction between two polar groups that occurs when a hydrogen (H) atom covalently bound to a highly electronegative atom such as nitrogen (N), oxygen (O), or fluorine (F) experiences the electrostatic field of another highly electronegative atom nearby.
Hydrogen bonds can occur between molecules (intermolecular) or within different parts of a single molecule (intramolecular).[4] Depending on the nature of the donor and acceptor atoms which constitute the bond, their geometry, and environment, the energy of a hydrogen bond can vary between 1 and 40 kcal/mol [5]. This makes them somewhat stronger than a van der Waals interaction, and usually weaker than covalent or ionic bonds. This type of bond can occur in inorganic molecules such as water and in organic molecules like DNA and proteins.
Intermolecular hydrogen bonding is responsible for the high boiling point of water (100 °C) compared to the other group 16 hydrides that have much weaker hydrogen bonds.[6] Intramolecular hydrogen bonding is partly responsible for the secondary and tertiary structures of proteins and nucleic acids. It also plays an important role in the structure of polymers, both synthetic and natural.
In 2011, an IUPAC Task Group recommended a modern evidence-based definition of hydrogen bonding, which was published in the IUPAC journal Pure and Applied Chemistry. This definition specifies:
The hydrogen bond is an attractive interaction between a hydrogen atom from a molecule or a molecular fragment X–H in which X is more electronegative than H, and an atom or a group of atoms in the same or a different molecule, in which there is evidence of bond formation.[7]
An accompanying detailed technical report provides the rationale behind the new definition.[8]
Contents
[hide]
1 Bonding
2 History
3 Hydrogen bonds in water
3.1 Bifurcated and over-coordinated hydrogen bonds in water
4 Hydrogen bonds in DNA and proteins
5 Hydrogen bonds in polymers
6 Symmetric hydrogen bond
7 Dihydrogen bond
8 Advanced theory of the hydrogen bond
9 Dynamics probed by spectroscopic means
10 Hydrogen bonding phenomena
11 References
12 Further reading
13 External links
Bonding[edit]
An example of intermolecular hydrogen bonding in a self-assembled dimer complex reported by Meijer and coworkers.[9] The hydrogen bonds are represented by dotted lines.
Intramolecular hydrogen bonding in acetylacetone helps stabilize the enol tautomer.
A hydrogen atom attached to a relatively electronegative atom will play the role of the hydrogen bond donor.[10] This electronegative atom is usually fluorine, oxygen, or nitrogen. A hydrogen attached to carbon can also participate in hydrogen bonding when the carbon atom is bound to electronegative atoms, as is the case in chloroform, CHCl3.[11][12][13] An example of a hydrogen bond donor is the hydrogen from the hydroxyl group of ethanol, which is bonded to an oxygen.
In a hydrogen bond, the electronegative atom not covalently attached to the hydrogen is named proton acceptor, whereas the one covalently bound to the hydrogen is named the proton donor.
Examples of hydrogen bond donating (donors) and hydrogen bond accepting groups (acceptors)
Cyclic dimer of acetic acid; dashed green lines represent hydrogen bonds
In the donor molecule, the electronegative atom attracts the electron cloud from around the hydrogen nucleus of the donor, and, by decentralizing the cloud, leaves the atom with a positive partial charge. Because of the small size of hydrogen relative to other atoms and molecules, the resulting charge, though only partial, represents a large charge density. A hydrogen bond results when this strong positive charge density attracts a lone pair of electrons on another heteroatom, which then becomes the hydrogen-bond acceptor.
The hydrogen bond is often described as an electrostatic dipole-dipole interaction. However, it also has some features of covalent bonding: it is directional and strong, produces interatomic distances shorter than the sum of the van der Waals radii, and usually involves a limited number of interaction partners, which can be interpreted as a type of valence. These covalent features are more substantial when acceptors bind hydrogens from more electronegative donors.
The partially covalent nature of a hydrogen bond raises the following questions: "To which molecule or atom does the hydrogen nucleus belong?" and "Which should be labeled 'donor' and which 'acceptor'?" Usually, this is simple to determine on the basis of interatomic distances in the X−H···Y system, where the dots represent the hydrogen bond: the X−H distance is typically ≈110 pm, whereas the H···Y distance is ≈160 to 200 pm. Liquids that display hydrogen bonding (such as water) are called associated liquids.
Hydrogen bonds can vary in strength from very weak (1–2 kJ mol−1) to extremely strong (161.5 kJ mol−1 in the ion HF−
2).[14][15] Typical enthalpies in vapor include:
F−H···:F (161.5 kJ/mol or 38.6 kcal/mol)
O−H···:N (29 kJ/mol or 6.9 kcal/mol)
O−H···:O (21 kJ/mol or 5.0 kcal/mol)
N−H···:N (13 kJ/mol or 3.1 kcal/mol)
N−H···:O (8 kJ/mol or 1.9 kcal/mol)
HO−H···:OH+
3 (18 kJ/mol[16] or 4.3 kcal/mol; data obtained using molecular dynamics as detailed in the reference and should be compared to 7.9 kJ/mol for bulk water, obtained using the same molecular dynamics.)
Quantum chemical calculations of the relevant interresidue potential constants (compliance constants) revealed[how?] large differences between individual H bonds of the same type. For example, the central interresidue N−H···N hydrogen bond between guanine and cytosine is much stronger in comparison to the N−H···N bond between the adenine-thymine pair.[17]
The length of hydrogen bonds depends on bond strength, temperature, and pressure. The bond strength itself is dependent on temperature, pressure, bond angle, and environment (usually characterized by local dielectric constant). The typical length of a hydrogen bond in water is 197 pm. The ideal bond angle depends on the nature of the hydrogen bond donor. The following hydrogen bond angles between a hydrofluoric acid donor and various acceptors have been determined experimentally:[18]
Acceptor···donor VSEPR geometry Angle (°)
HCN···HF linear 180
H2CO···HF trigonal planar 120
H2O···HF pyramidal 46
H2S···HF pyramidal 89
SO2···HF trigonal 142
History[edit]
In the book The Nature of the Chemical Bond, Linus Pauling credits T. S. Moore and T. F. Winmill with the first mention of the hydrogen bond, in 1912.[19][20] Moore and Winmill used the hydrogen bond to account for the fact that trimethylammonium hydroxide is a weaker base than tetramethylammonium hydroxide. The description of hydrogen bonding in its better-known setting, water, came some years later, in 1920, from Latimer and Rodebush.[21] In that paper, Latimer and Rodebush cite work by a fellow scientist at their laboratory, Maurice Loyal Huggins, saying, "Mr. Huggins of this laboratory in some work as yet unpublished, has used the idea of a hydrogen kernel held between two atoms as a theory in regard to certain organic compounds."
Hydrogen bonds in water[edit]
Crystal structure of hexagonal ice. Gray dashed lines indicate hydrogen bonds
The most ubiquitous and perhaps simplest example of a hydrogen bond is found between water molecules. In a discrete water molecule, there are two hydrogen atoms and one oxygen atom. Two molecules of water can form a hydrogen bond between them; the simplest case, when only two molecules are present, is called the water dimer and is often used as a model system. When more molecules are present, as is the case with liquid water, more bonds are possible because the oxygen of one water molecule has two lone pairs of electrons, each of which can form a hydrogen bond with a hydrogen on another water molecule. This can repeat such that every water molecule is H-bonded with up to four other molecules, as shown in the figure (two through its two lone pairs, and two through its two hydrogen atoms). Hydrogen bonding strongly affects the crystal structure of ice, helping to create an open hexagonal lattice. The density of ice is less than the density of water at the same temperature; thus, the solid phase of water floats on the liquid, unlike most other substances.
Liquid water's high boiling point is due to the high number of hydrogen bonds each molecule can form, relative to its low molecular mass. Owing to the difficulty of breaking these bonds, water has a very high boiling point, melting point, and viscosity compared to otherwise similar liquids not conjoined by hydrogen bonds. Water is unique because its oxygen atom has two lone pairs and two hydrogen atoms, meaning that the total number of bonds of a water molecule is up to four. For example, hydrogen fluoride—which has three lone pairs on the F atom but only one H atom—can form only two bonds; (ammonia has the opposite problem: three hydrogen atoms but only one lone pair).
H−F···H−F···H−F
The exact number of hydrogen bonds formed by a molecule of liquid water fluctuates with time and depends on the temperature.[22] From TIP4P liquid water simulations at 25 °C, it was estimated that each water molecule participates in an average of 3.59 hydrogen bonds. At 100 °C, this number decreases to 3.24 due to the increased molecular motion and decreased density, while at 0 °C, the average number of hydrogen bonds increases to 3.69.[22] A more recent study found a much smaller number of hydrogen bonds: 2.357 at 25 °C.[23] The differences may be due to the use of a different method for defining and counting the hydrogen bonds.
Where the bond strengths are more equivalent, one might instead find the atoms of two interacting water molecules partitioned into two polyatomic ions of opposite charge, specifically hydroxide (OH−) and hydronium (H3O+). (Hydronium ions are also known as "hydroxonium" ions.)
H−O− H3O+
Indeed, in pure water under conditions of standard temperature and pressure, this latter formulation is applicable only rarely; on average about one in every 5.5 × 108 molecules gives up a proton to another water molecule, in accordance with the value of the dissociation constant for water under such conditions. It is a crucial part of the uniqueness of water.
Because water may form hydrogen bonds with solute proton donors and acceptors, it may competitively inhibit the formation of solute intermolecular or intramolecular hydrogen bonds. Consequently, hydrogen bonds between or within solute molecules dissolved in water are almost always unfavorable relative to hydrogen bonds between water and the donors and acceptors for hydrogen bonds on those solutes.[24] Hydrogen bonds between water molecules have an average lifetime of 10−11 seconds, or 10 picoseconds.[25]
Bifurcated and over-coordinated hydrogen bonds in water[edit]
A single hydrogen atom can participate in two hydrogen bonds, rather than one. This type of bonding is called "bifurcated" (split in two or "two-forked"). It can exist, for instance, in complex natural or synthetic organic molecules.[26] It has been suggested that a bifurcated hydrogen atom is an essential step in water reorientation.[27]
Acceptor-type hydrogen bonds (terminating on an oxygen's lone pairs) are more likely to form bifurcation (it is called overcoordinated oxygen, OCO) than are donor-type hydrogen bonds, beginning on the same oxygen's hydrogens.[28]
Hydrogen bonds in DNA and proteins[edit]
The structure of part of a DNA double helix
Hydrogen bonding between guanine and cytosine, one of two types of base pairs in DNA
Hydrogen bonding also plays an important role in determining the three-dimensional structures adopted by proteins and nucleic bases. In these macromolecules, bonding between parts of the same macromolecule cause it to fold into a specific shape, which helps determine the molecule's physiological or biochemical role. For example, the double helical structure of DNA is due largely to hydrogen bonding between its base pairs (as well as pi stacking interactions), which link one complementary strand to the other and enable replication.
In the secondary structure of proteins, hydrogen bonds form between the backbone oxygens and amide hydrogens. When the spacing of the amino acid residues participating in a hydrogen bond occurs regularly between positions i and i + 4, an alpha helix is formed. When the spacing is less, between positions i and i + 3, then a 310 helix is formed. When two strands are joined by hydrogen bonds involving alternating residues on each participating strand, a beta sheet is formed. Hydrogen bonds also play a part in forming the tertiary structure of protein through interaction of R-groups. (See also protein folding).
The role of hydrogen bonds in protein folding has also been linked to osmolyte-induced protein stabilization. Protective osmolytes, such as trehalose and sorbitol, shift the protein folding equilibrium toward the folded state, in a concentration dependent manner. While the prevalent explanation for osmolyte action relies on excluded volume effects, that are entropic in nature, recent circular dichroism (CD) experiments have shown osmolyte to act through an enthalpic effect.[29] The molecular mechanism for their role in protein stabilization is still not well established, though several mechanism have been proposed. Recently, computer molecular dynamics simulations suggested that osmolytes stabilize proteins by modifying the hydrogen bonds in the protein hydration layer.[30]
Several studies have shown that hydrogen bonds play an important role for the stability between subunits in multimeric proteins. For example, a study of sorbitol dehydrogenase displayed an important hydrogen bonding network which stabilizes the tetrameric quaternary structure within the mammalian sorbitol dehydrogenase protein family.[31]
A protein backbone hydrogen bond incompletely shielded from water attack is a dehydron. Dehydrons promote the removal of water through proteins or ligand binding. The exogenous dehydration enhances the electrostatic interaction between the amide and carbonyl groups by de-shielding their partial charges. Furthermore, the dehydration stabilizes the hydrogen bond by destabilizing the nonbonded state consisting of dehydrated isolated charges.[32]
Hydrogen bonds in polymers[edit]
Para-aramid structure
A strand of cellulose (conformation Iα), showing the hydrogen bonds (dashed) within and between cellulose molecules
Many polymers are strengthened by hydrogen bonds in their main chains. Among the synthetic polymers, the best known example is nylon, where hydrogen bonds occur in the repeat unit and play a major role in crystallization of the material. The bonds occur between carbonyl and amine groups in the amide repeat unit. They effectively link adjacent chains to create crystals, which help reinforce the material. The effect is greatest in aramid fibre, where hydrogen bonds stabilize the linear chains laterally. The chain axes are aligned along the fibre axis, making the fibres extremely stiff and strong. Hydrogen bonds are also important in the structure of cellulose and derived polymers in its many different forms in nature, such as wood and natural fibres such as cotton and flax.
The hydrogen-bond networks make both natural and synthetic polymers sensitive to humidity levels in the atmosphere because water molecules can diffuse into the surface and disrupt the network. Some polymers are more sensitive than others. Thus nylons are more sensitive than aramids, and nylon 6 more sensitive than nylon-11.
Symmetric hydrogen bond[edit]
A symmetric hydrogen bond is a special type of hydrogen bond in which the proton is spaced exactly halfway between two identical atoms. The strength of the bond to each of those atoms is equal. It is an example of a three-center four-electron bond. This type of bond is much stronger than a "normal" hydrogen bond. The effective bond order is 0.5, so its strength is comparable to a covalent bond. It is seen in ice at high pressure, and also in the solid phase of many anhydrous acids such as hydrofluoric acid and formic acid at high pressure. It is also seen in the bifluoride ion [F−H−F]−.
Symmetric hydrogen bonds have been observed recently spectroscopically in formic acid at high pressure (>GPa). Each hydrogen atom forms a partial covalent bond with two atoms rather than one. Symmetric hydrogen bonds have been postulated in ice at high pressure (Ice X). Low-barrier hydrogen bonds form when the distance between two heteroatoms is very small.
Dihydrogen bond[edit]
The hydrogen bond can be compared with the closely related dihydrogen bond, which is also an intermolecular bonding interaction involving hydrogen atoms. These structures have been known for some time, and well characterized by crystallography;[33] however, an understanding of their relationship to the conventional hydrogen bond, ionic bond, and covalent bond remains unclear. Generally, the hydrogen bond is characterized by a proton acceptor that is a lone pair of electrons in nonmetallic atoms (most notably in the nitrogen, and chalcogen groups). In some cases, these proton acceptors may be pi-bonds or metal complexes. In the dihydrogen bond, however, a metal hydride serves as a proton acceptor, thus forming a hydrogen-hydrogen interaction. Neutron diffraction has shown that the molecular geometry of these complexes is similar to hydrogen bonds, in that the bond length is very adaptable to the metal complex/hydrogen donor system.[33]
Advanced theory of the hydrogen bond[edit]
In 1999, Isaacs et al.[34] showed from interpretations of the anisotropies in the Compton profile of ordinary ice that the hydrogen bond is partly covalent. However, this interpretation was challenged by Ghanty et al.,[35] who concluded that considering electrostatic forces alone could explain the experimental results. Some NMR data on hydrogen bonds in proteins also indicate covalent bonding.
Most generally, the hydrogen bond can be viewed as a metric-dependent electrostatic scalar field between two or more intermolecular bonds. This is slightly different from the intramolecular bound states of, for example, covalent or ionic bonds; however, hydrogen bonding is generally still a bound state phenomenon, since the interaction energy has a net negative sum. The initial theory of hydrogen bonding proposed by Linus Pauling suggested that the hydrogen bonds had a partial covalent nature. This remained a controversial conclusion until the late 1990s when NMR techniques were employed by F. Cordier et al. to transfer information between hydrogen-bonded nuclei, a feat that would only be possible if the hydrogen bond contained some covalent character.[36] While much experimental data has been recovered for hydrogen bonds in water, for example, that provide good resolution on the scale of intermolecular distances and molecular thermodynamics, the kinetic and dynamical properties of the hydrogen bond in dynamic systems remain unchanged.
Dynamics probed by spectroscopic means[edit]
The dynamics of hydrogen bond structures in water can be probed by the IR spectrum of OH stretching vibration.[37] In the hydrogen bonding network in protic organic ionic plastic crystals (POIPCs), which are a type of phase change material exhibiting solid-solid phase transitions prior to melting, variable-temperature infrared spectroscopy can reveal the temperature dependence of hydrogen bonds and the dynamics of both the anions and the cations.[38] The sudden weakening of hydrogen bonds during the solid-solid phase transition seems to be coupled with the onset of orientational or rotational disorder of the ions.[38]
Hydrogen bonding phenomena[edit]
Dramatically higher boiling points of NH3, H2O, and HF compared to the heavier analogues PH3, H2S, and HCl.
Increase in the melting point, boiling point, solubility, and viscosity of many compounds can be explained by the concept of hydrogen bonding.
Occurrence of proton tunneling during DNA replication is believed to be responsible for cell mutations.[39]
Viscosity of anhydrous phosphoric acid and of glycerol
Dimer formation in carboxylic acids and hexamer formation in hydrogen fluoride, which occur even in the gas phase, resulting in gross deviations from the ideal gas law.
Pentamer formation of water and alcohols in apolar solvents.
High water solubility of many compounds such as ammonia is explained by hydrogen bonding with water molecules.
Negative azeotropy of mixtures of HF and water
Deliquescence of NaOH is caused in part by reaction of OH− with moisture to form hydrogen-bonded H
3O−
2 species. An analogous process happens between NaNH2 and NH3, and between NaF and HF.
The fact that ice is less dense than liquid water is due to a crystal structure stabilized by hydrogen bonds.
The presence of hydrogen bonds can cause an anomaly in the normal succession of states of matter for certain mixtures of chemical compounds as temperature increases or decreases. These compounds can be liquid until a certain temperature, then solid even as the temperature increases, and finally liquid again as the temperature rises over the "anomaly interval"[40]
Smart rubber utilizes hydrogen bonding as its sole means of bonding, so that it can "heal" when torn, because hydrogen bonding can occur on the fly between two surfaces of the same polymer.
Strength of nylon and cellulose fibres.
Wool, being a protein fibre, is held together by hydrogen bonds, causing wool to recoil when stretched. However, washing at high temperatures can permanently break the hydrogen bonds and a garment may permanently lose its shape.
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^ Jump up to: a b Luo, Jiangshui; Jensen, Annemette H.; Brooks, Neil R.; Sniekers, Jeroen; Knipper, Martin; Aili, David; Li, Qingfeng; Vanroy, Bram; Wübbenhorst, Michael; Yan, Feng; Van Meervelt, Luc; Shao, Zhigang; Fang, Jianhua; Luo, Zheng-Hong; De Vos, Dirk E.; Binnemans, Koen; Fransaer, Jan (2015). "1,2,4-Triazolium perfluorobutanesulfonate as an archetypal pure protic organic ionic plastic crystal electrolyte for all-solid-state fuel cells". Energy & Environmental Science. 8 (4): 1276. doi:10.1039/C4EE02280G.
Jump up ^ Löwdin, P. O. (1963). "Proton Tunneling in DNA and its Biological Implications". Rev. Mod. Phys. 35 (3): 724. Bibcode:1963RvMP...35..724L. doi:10.1103/RevModPhys.35.724.
Jump up ^ Law-breaking liquid defies the rules. Physicsworld.com (September 24, 2004 )
Further reading[edit]
George A. Jeffrey. An Introduction to Hydrogen Bonding (Topics in Physical Chemistry). Oxford University Press, USA (March 13, 1997). ISBN 0-19-509549-9
External links[edit]
The Bubble Wall (Audio slideshow from the National High Magnetic Field Laboratory explaining cohesion, surface tension and hydrogen bonds)
isotopic effect on bond dynamics
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Football helmet
From Wikipedia, the free encyclopedia
Jump to: navigation, search
The helmet used by the Tampa Bay Buccaneers from 1997–2013.
This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (July 2009) (Learn how and when to remove this template message)
The football helmet is a piece of protective equipment used mainly in American football and Canadian football. It consists of a hard plastic shell with thick padding on the inside, a face mask made of one or more plastic-coated metal bars, and a chinstrap. Each position has a different type of face mask to balance protection and visibility, and some players add polycarbonate visors to their helmets, which are used to protect their eyes from glare and impacts. Helmets are a requirement at all levels of organized football, except for non-tackle variations such as flag football. Although they are protective, players can and do still suffer head injuries such as concussions.
Contents
[hide]
1 History
1.1 Invention
1.2 Early years
1.3 Introduction of advanced materials
2 Modern helmet components
2.1 Inflatable padding
2.2 Visors
2.3 Sensors
2.4 Headsets
2.5 One-bar face masks
3 Recent designs
4 Safety research and testing
4.1 NOCSAE certification
4.2 Current research
4.3 Other research
5 Logo display
5.1 National Football League
6 See also
7 References
8 External links
History[edit]
Main article: History of the football helmet
Football team, turn of the 20th century
Invention[edit]
One of the first instances of football headgear dates to 1896 when Lafayette College halfback George "Rose" Barclay began to use straps and earpieces to protect his ears. It is not certain who invented the football helmet. Many sources give credit for the creation of the helmet to James Naismith, while other sources credit U.S. Naval Academy Midshipman Joseph M. Reeves (later to become the "Father of Carrier Aviation"), who had a protective device for his head made out of mole skin to allow him to play in the 1893 Army-Navy game. Reeves had been advised by a Navy doctor that another kick to his head would result in "instant insanity" or even death, so he commissioned an Annapolis shoemaker to make him a helmet out of leather.[1] Later, helmets were made of padded leather and resembled aviators' helmets or modern day scrum caps. At least in professional football, they were optional. Some National Football League players, notably Hall-of-Famer Bill Hewitt, played all or most of their careers without a helmet.
Early years[edit]
One innovation from the early 1900s period was hardened leather. 1917 marked the first time helmets were raised above the head in an attempt to direct blows away from the top of the head.[clarification needed] Ear flaps also had their downfall during this period as they had little ventilation and made it difficult for players to hear. The 1920s marked the first time that helmets were widely used in the sport of football. These helmets were made of leather and had some padding on the inside, but the padding was insufficient and provided little protection. In addition, they lacked face masks. As a result, injuries were very common. Early helmets also absorbed a lot of heat, making them very uncomfortable to wear.
A leather football helmet believed to have been worn by Gerald Ford while playing for the University of Michigan between 1932 and 1934.
In 1939, the Riddell Company of Chicago, Illinois started manufacturing plastic helmets because it felt that plastic helmets would be safer than those made of leather. Plastic was found to be more effective because it held its shape when full collision contact occurred on a play. These helmets were also much more comfortable and had more padding to cushion the head in an impact. Included with the plastic helmet came plastic face mask, which allowed the helmet to protect the entire head. By the mid-1940s, helmets were required in the NFL. They were still made of leather, but with improved manufacturing techniques had assumed their more familiar spherical shape. The NFL initially allowed either plastic or leather helmets, but in 1948 the league outlawed the plastic helmet, considering the hard-plastic material to be an injury risk. The NFL repealed this rule in 1949, and by 1950, the plastic helmet had become universal in that league.[2]
Introduction of advanced materials[edit]
By the 1950s, the introduction of polymers ended the leather helmet era. The last leather helmet manufacturer, MacGregor, ceased production of leather helmets in the mid-1960s. The NFL also recommended face masks for players in 1955,[3] reducing the number of broken noses and teeth, but also necessitating new rules prohibiting opposing players from grabbing the face mask. By varying accounts, either Pat Studstill or Garo Yepremian was the last to forgo the facemask; among non-kickers, Tommy McDonald was the last to do so.
Modern helmet components[edit]
2015 Cleveland Browns helmet
Inflatable padding[edit]
According to Andrew Tucker, football helmets adequately protected players from catastrophic brain injuries, but helmet manufacturers were motivated to design helmets that decrease the risk of concussions. Vin Ferrara,{[4]} a former Harvard quarterback, accidentally discovered a new way to cushion football helmets. One night, Ferrara was looking for an aspirin when he saw a squirt bottle in his medicine cabinet. As he pumped it and then punched it, he realized that the bottle withstood the blows of different forces. Ferrara immediately came up with the idea to encase football helmets with a number of inflatable pockets in order to cushion the blows a football player receives and reduce concussions.
More recently, in 2003 Schutt sports introduced their football helmets which contained TPU, or thermoplastic urethane. They would argue that this helps cushion the head more than any other helmet in the market. Schutt also believes that TPU makes the helmet less prone to mold and easier overall to clean and keep sanitary.[5]
Visors[edit]
A more recent addition to the football helmet is the visor or eye shield, which is affixed to the face mask to protect players from glare or eye injuries, such as pokes. It is believed that the first player to use a protective visor Mark Mullaney of the NFL's Minnesota Vikings in 1984, in order to protect a healing eye injury. Top manufacturers of visors are Nike, Oakley, and Under Armour, with Leader being the first to come out with a visor/shield for former Chicago Bears quarterback Jim McMahon (who needed the visor because of a childhood eye injury).[citation needed] While Mullaney and McMahon's visors were tinted, most of the earlier visors were clear or smoked, but they are now offered in a variety of styles ranging from blue, gold, black, rainbow, silver, or amber. High-school and pee-wee leagues prohibit all but clear visors. This rule was enacted so that training staff and coaches can easily view a player's face and eyes in the case of a serious injury, to discern if the player is conscious.[citation needed] The NCAA banned the use of tinted visors for the same reason, and the NFL has followed suit as well. However, players with eye problems may still obtain special permission to wear tinted visors, some notable examples being LaDainian Tomlinson and Chris Canty.[6]
Players from the United States Air Force Academy in Colorado Springs wearing football helmets during a drill in 2004
Sensors[edit]
Helmet shock data loggers and shock detectors monitor impacts a player receives, such as the force and direction of the impact. If the force recorded by the sensors is over 100 Gs, it signals a possible concussion.{[7]} Some players will experience up to 2,000 of these potential concussion blows each season.This data is then analyzed by doctors. New rules have been implemented which instruct that any player who has a particularly high reading of force needs to be taken off the field and examined before they can play another down.
Headsets[edit]
Two Ohio inventors devised a headset for Cleveland Browns coach Paul Brown so he could radio plays to his quarterback. It was banned shortly after its first use in 1956. The NFL approved use of headsets for all NFL teams in 1994.[8]
NFL rules state that all helmets equipped with headsets must have a visible green dot on the back. A few times in 2006, the holder on the field goal attempt was told to pull up and throw or run at the last second because of a change the coaches saw on the field. According to the NFL, this gave teams an "unfair advantage." The new rules let each team know who is wearing a headset and hearing the plays being called.[citation needed]
Kevin Grady wearing the winged football helmet.
One-bar face masks[edit]
The one-bar face mask was once common but its use has been supplanted in professional and amateur sport. For example, it has been illegal in the National Football League since 2004, but a grandfather clause allowed players who wore the mask prior to 2004 to continue to do so for the remainder of their careers. No current professional player currently wears such a face mask; the last player to do so was Scott Player, who last played professionally in 2009.
Typically, by the mid-1980s only placekickers and punters in professional football in Canada and the United States wore the one-bar face mask, a notable exception being quarterback Joe Theismann.
The one-bar had two different variations. The standard one-bar was made from nylon or other hard plastic and was bolted to both side of the helmet just in front of the earholes. There was a "snub" version that did not extend as far out in front of the helmet as the standard.
Face masks for football helmets today are multibar. The multibar facemasks are typically constructed out of metal, such as titanium, stainless steel, or most commonly carbon steel. Each facemask is coated with Polyarmor G17, a powder coating that is resistant to impact and corrosion. The Polyarmor is a thermoplastic coating used on a number of surfaces. While some organizations purchase new face masks every season, others have their equipment reconditioned.
Recent designs[edit]
In 2002, American football equipment manufacturer Riddell released a new design of helmet called the Revolution.[9] The newer design was released in response to a study on concussions. In addition, Riddell has recently come out with a new design of helmets, the Riddell Speed Flex. This helmet came out in 2014.[10] This new helmet uses elements of Riddell's older helmets, the 360 and the Revolution, such as Side Impact Protection and All Points Quick Release face mask attachment system.[11]
Iowa St Riddell Speed Helmet
In 2007, Schutt Sports announced the arrival of a next generation helmet, the Schutt ION 4D. This next generation design was in response to the demand for a safer football helmet. The design includes an integrated face guard. This new face guard design features shock absorbing "Energy Wedges" that reduce the force of impacts to the face guard. College teams wearing the helmet include Air Force, Penn State and Virginia.[12] Schutt has also distinguished between their varsity helmets and youth helmets. The varsity helmets from Schutt are made with polycarbonate, which is a very strong polymer designed to take bigger hits. The Schutt youth helmets however; are made from ABS, which is a lighter material, meant for kids who do not take as powerful of hits.[5]
Recently, a brand new type of helmet has come into play. Vicis is a new company that is producing helmets that have a softer outer layer. The softer layer absorbs more energy from impacts. In addition, the inside of the helmet also has a foam like substance which absorbs energy and improves comfort.[13]
Safety research and testing[edit]
NOCSAE certification[edit]
Main article: National Operating Committee on Standards for Athletic Equipment
Rules in place for NFL, NCAA, and high school football require that all helmets be certified by the National Operating Committee on Standards for Athletic Equipment.[14][15][16] Reliance on NOCSAE certification has been criticized on numerous grounds, including that organization's control by equipment manufacturers causes a conflict of interest, testing data that focuses on skull fractures instead of concussions, and failure to take into account new research.[14][17][18]
The most common NOCSAE test is the drop test. This test uses a 13-pound dummy head full of sensors and a gelatin material. The head and helmet is dropped from a height of 60 at one of the six NOCSAE specified locations on the helmet. These locations include the front, rear, left side, right side, right boss, and left boss. The sensors in the dummy head measure the amount of force that the head experiences. The NOCSAE has certain regulations such as the peak severity index can never more than1200 SI. If a helmet fails to meet these requirements, they do not pass the NOCSAE drop test.[19][20]
Current research[edit]
There has been significant study/research regarding head injuries in football, as well as football helmet design in recent years. Kevin Guskiewicz, a professor at The University of North Carolina and a MacArthur Fellow, has for many years been researching concussions in football of all age groups.[21] He has been equipping UNC football helmets with accelerometers to measure impacts and concussions. Also, the NFL has awarded over $1.6 million in sports medical research, almost $1 million of which has been toward concussion prevention.[22] All this concussion prevention research has led football helmet manufacturers to develop safer products. A joint effort between Virginia Tech and Wake Forest has been testing current football helmets and giving them yearly ratings since 2011. On a scale out of 5 stars, only one helmet was awarded a 5 in 2011. In 2012, two additional helmet designs were awarded 5 stars.[23][24]
Controversies revolving around football helmets always regard their ability to decrease head/brain injury rates, including concussions. However, recent research has begun to assess the tests specifically employed to create the safest football equipment. In 2015, David Camarillo at Stanford conducted a study that suggested football helmet tests did not account for the delay between injury-causing brain movement and stress impact.[25]
Other research[edit]
Neuroscientists at Ohio State University launched baseballs from air cannons at football helmets in order to simulate a kick or blow to the head such as a tackle. It was found that the helmets could withstand 2,500 Newtons or about 562 pounds of force.
Vijay Gupta, a professor at UCLA, has done research and produced a special polymer that if added as a layer on the inside of football helmets can produce up to a 25% decrease in the g-forces a player would experience.[26] This reduction of forces would produce a similar amount of reduction of the probability of a player suffering a concussion from the same hits.
Logo display[edit]
National Football League[edit]
In 1948, the Los Angeles Rams were the first NFL team to put logos on their helmets; the basic "ram's horn" logo on the helmet has remained mostly the same, except for color, ever since. As of 2018 the Cleveland Browns are the last remaining NFL teams not using any form of primary logo on its helmets. The Pittsburgh Steelers are the only NFL team that puts its logo on only one side of the helmet (the right side), while the Cincinnati Bengals, after using a wordmark for a helmet logo into the 1980s, use a striping pattern instead of a logo.
See also[edit]
The Helmet Project
History of the football helmet
References[edit]
Notes
Jump up ^ "History of the Football Helmet". Past Time Sports. Retrieved 2011-02-02.
Jump up ^ http://www.helmethut.com/062102.html
Jump up ^ Factory Made television program, segment entitled "Football helmets", Science Channel.
Jump up ^ Shwartz, Alan. "Helmet Design Absorbs Shock in a New Way" The New Your Times. 2007 https://www.nytimes.com/2007/10/27/sports/football/27helmets.html
^ Jump up to: a b "The Science of Domination | Schutt Sports". www.schuttsports.com. Retrieved 2017-05-14.
Jump up ^ Keep On Tickin’ Posted 2006-08-25: The NCAA hopes its new rules shorten games this season.[permanent dead link]
Jump up ^ University of Denver. "Most concussions deliver 95 g's, neuropsychologist says." ScienceDaily. ScienceDaily, 25 June 2010. <www.sciencedaily.com/releases/2010/06/100624092526.htm>.
Jump up ^ http://operations.nfl.com/the-game/technology/
Jump up ^ Riddell: Product Detail[permanent dead link]
Jump up ^ "Riddell gaining attention with new Speedflex, updated technology". NFL.com. Retrieved 2017-05-14.
Jump up ^ "About Riddell Speedflex Helmet - Buy New Football Impact Helmets". www.riddell.com. Retrieved 2017-05-14.
Jump up ^ Schutt ION-4D Who's in it?, football helmets, baseball, softball bats
Jump up ^ "This Football Helmet Crumples—and That's Good". Bloomberg.com. Retrieved 2017-05-14.
^ Jump up to: a b Borden, Sam (September 20, 2012). "Despite Risks, N.F.L. Leaves Helmet Choices in Players' Hands". New York Times. Archived from the original on September 21, 2012.
Jump up ^ Hillman, Kay (2005). Introduction To Athletic Training. Human Kinetics. ISBN 9780736052924.
Jump up ^ Nelson, David M. (1994). The Anatomy of a Game: Football, the Rules, and the Men Who Made the Game. University of Delaware. p. 510. ISBN 9780874134551.
Jump up ^ Nowinski, Chris (2006). Head Games: Football's Concussion Crisis from the NFL to Youth Leagues. pp. 110, 116. ISBN 9781597630139.
Jump up ^ Culverhouse, Gay (2011). Throwaway Players: Concussion Crisis From Pee Wee Football to the NFL. Behler Publications. p. 79. ISBN 9781933016702.
Jump up ^ http://www.nj.com/rutgersfootball/index.ssf/2017/04/behind_the_scenes_look_at_how_a_rutgers_nfl_or_hig.html
Jump up ^ http://nocsae.org/wp-content/files_mf/1436291444ND00213m15MfrdFBHelmetsStandardPerformance.pdf
Jump up ^ http://www.unc.edu/spotlight/Guskiewicz-wins-MacArthur
Jump up ^ http://www.nfl.com/news/story/09000d5d81d15901/printable/nfl-charities-awards-grants-for-sports-medical-research
Jump up ^ "Archived copy". Archived from the original on 2012-06-01. Retrieved 2012-05-24.
Jump up ^ http://www.sbes.vt.edu/nid
Jump up ^ University, Stanford (2015-07-20). "Stanford research: football helmet tests may not account for concussion-prone actions". Stanford News. Retrieved 2017-05-15.
Jump up ^ http://newsroom.ucla.edu/stories/developing-new-materials-to-prevent-248008
Sources
Albergotti, Reed and Wang, Shirley S. "Is it time to retire the football helmet?" The Wall Street Journal (November 11, 2009)
Bhattacharji, Alex. "Helmet History" Sports Illustrated for Kids (October 1996)
Copeland, Michael V. "Crash Pad" Fortune International (February 8, 2010) p.8
Schwartz, Alan. "Concussion- New Football Helmet Design" The New York Times (October 27, 2007)
Tucker, Andrew M. "Football players head injuries" House Judiciary FDCH Congressional Testimony (October 28, 2009)
Zarda, Brett. "Butting Heads" Popular Science (September 2007)
External links[edit]
Wikimedia Commons has media related to American football helmets.
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Geothermal power in Iceland
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Geothermal borehole outside the Reykjanes Power Station
Due to the geological location of Iceland (over a rift in continental plates), the high concentration of volcanoes in the area is often an advantage in the generation of geothermal energy, the heating and making of electricity.[1] During winter, pavements near these areas (such as Reykjavik and Akureyri) are heated up.
Five major geothermal power plants exist in Iceland, which produce approximately 26.2% (2010)[2] of the nation's electricity. In addition, geothermal heating meets the heating and hot water requirements of approximately 87% of all buildings in Iceland. Apart from geothermal energy, 73.8% of the nation’s electricity is generated by hydro power,[3] and 0.1% from fossil fuels.[4]
Consumption of primary geothermal energy in 2004 was 79.7 petajoules (PJ), approximately 53.4% of the total national consumption of primary energy, 149.1 PJ. The corresponding share for hydro power was 17.2%, petroleum was 26.3%, and coal was 3%.[5] Plans are underway to turn Iceland into a 100% fossil-fuel-free nation in the near future.[6] For example, Iceland's abundant geothermal energy has enabled renewable energy initiatives, such as Carbon Recycling International's carbon dioxide to methanol fuel process.[7] The following are the five largest power stations in Iceland.[8]
Geothermal energy also provides tourist attractions such as the Blue Lagoon. The geothermal water originates 2,000 metres below the surface, where freshwater and seawater combine at extreme temperatures. It is then harnessed via drilling holes at a nearby geothermal power plant, Svartsengi, to create electricity and hot water for nearby communities. This Blue Lagoon is based upon an amazing gift of nature driven by a respect from the natural environment and 100% powered by clean geothermal energy.[9]
Hellisheiði Power Station (303 MW)
Nesjavellir Geothermal Power Station (120 MW)
Reykjanes Power Station (100 MW)
Svartsengi Power Station (76.5 MW)
Krafla Power Station (60 MW)
Þeistareykir Power Station (45 MW)
Above is the tectonic plate rifts of Iceland, with NVZ being the largest of all of them. There are many volcanoes that run along this rift including Peistareykir, Krafla, Fremri Námar, Askja, Tungnafellsjökull, Hágongur, Hekla, Vatnafjöll, Katla, Torfajökull, and Eyjafjallajökull. This rift runs from Akureyri to Reykjavik.
See also[edit]
List of power stations in Iceland
Renewable energy in Iceland
The Geothermal energy exhibition
Iceland Deep Drilling Project
Renewable energy by country
References[edit]
Jump up ^ Icelandic Energy Portal
Jump up ^ "Archived copy". Archived from the original on 2012-10-31. Retrieved 2015-04-30.
Jump up ^ "Raforkuvinnsla". landsvirkjun.is. Archived from the original on 31 October 2012. Retrieved 30 April 2015.
Jump up ^ Ministry of Industries and Innovation, Iceland (19 March 2014). "The Icelandic National Renewable Energy Action Plan for the promotion of the use of energy from renewable sources in accordance with Directive 2009/28/EC and the Commission Decision of 30 June 2009 on a template for the national renewable energy action plans" (PDF). European Comission. p. 3.
Jump up ^ "Energy in Iceland - Historical Perspective, Present Status, Future Outlook" (PDF). Orkustofnun (Iceland Energy Authority). Retrieved 2006-09-20.
Jump up ^ "Energy Statistics in Iceland" (PDF). Orkustofnun (Iceland Energy Authority). Retrieved 2006-09-20.
Jump up ^ "Technology". Carbon Recycling International. 2011. Archived from the original on 17 June 2013. Retrieved 11 July 2012.
Jump up ^ Icelandic Energy Portal
Jump up ^ Badaoui, Bachir. "Geothermal Energy - Blue Lagoon". Smithsonian.com.
External links[edit]
Iceland Energy Authority
Icelandic Energy Portal
More information about Svartsengi power-plant
More information about Nesjavellir power-plant
More information about Krafla power-plant
More information about Hellisheidi power-plant
Photo Gallery from islandsmyndir.is
Photo Geothermal power station Svartsengi
Photos of Geothermal power plants at Reykjanes & Svartsengi
Tiroler Bi
Mannvit Engineering of Iceland
RES - School for Renewable Energy Science in Iceland
Keilir - Atlantic Center of Excellence
Icelandic GeoSurvey
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