Osmotic power

From Wikipedia, the free encyclopedia

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

 

Osmotic power, salinity gradient power or blue energy is the energy available from the difference in the salt concentration between seawater and river water. Two practical methods for this are reverse electrodialysis (RED) and pressure retarded osmosis (PRO). Both processes rely on osmosis with membranes. The key waste product is brackish water. This byproduct is the result of natural forces that are being harnessed: the flow of fresh water into seas that are made up of salt water.

In 1954, Pattle suggested that there was an untapped source of power when a river mixes with the sea, in terms of the lost osmotic pressure, however it was not until the mid ‘70s where a practical method of exploiting it using selectively permeable membranes by Loeb was outlined.

The method of generating power by pressure retarded osmosis was invented by Prof. Sidney Loeb in 1973 at the Ben-Gurion University of the Negev, Beersheba, Israel. The idea came to Prof. Loeb, in part, as he observed the Jordan River flowing into the Dead Sea. He wanted to harvest the energy of mixing of the two aqueous solutions (the Jordan River being one and the Dead Sea being the other) that was going to waste in this natural mixing process. In 1977 Prof. Loeb invented a method of producing power by a reverse electrodialysis heat engine.

The technologies have been confirmed in laboratory conditions. They are being developed into commercial use in the Netherlands (RED) and Norway (PRO). The cost of the membrane has been an obstacle. A new, lower cost membrane, based on an electrically modified polyethylene plastic, made it fit for potential commercial use. Other methods have been proposed and are currently under development. Among them, a method based on electric double-layer capacitor technology. and a method based on vapor pressure difference.

Basics of salinity gradient power

Pressure-retarded osmosis

 

Salinity gradient power is a specific renewable energy alternative that creates renewable and sustainable power by using naturally occurring processes. This practice does not contaminate or release carbon dioxide (CO₂) emissions (vapor pressure methods will release dissolved air containing CO₂ at low pressures—these non-condensable gases can be re-dissolved of course, but with an energy penalty). Also as stated by Jones and Finley within their article “Recent Development in Salinity Gradient Power”, there is basically no fuel cost.

Salinity gradient energy is based on using the resources of “osmotic pressure difference between fresh water and sea water.” All energy that is proposed to use salinity gradient technology relies on the evaporation to separate water from salt. Osmotic pressure is the "chemical potential of concentrated and dilute solutions of salt". When looking at relations between high osmotic pressure and low, solutions with higher concentrations of salt have higher pressure.

Differing salinity gradient power generations exist but one of the most commonly discussed is pressure-retarded osmosis (PRO). Within PRO seawater is pumped into a pressure chamber where the pressure is lower than the difference between fresh and salt water pressure. Fresh water moves in a semipermeable membrane and increases its volume in the chamber. As the pressure in the chamber is compensated a turbine spins to generate electricity. In Braun's article he states that this process is easy to understand in a more broken down manner. Two solutions, A being salt water and B being fresh water are separated by a membrane. He states "only water molecules can pass the semipermeable membrane. As a result of the osmotic pressure difference between both solutions, the water from solution B thus will diffuse through the membrane in order to dilute solution A". The pressure drives the turbines and power the generator that produces the electrical energy. Osmosis might be used directly to "pump" fresh water out of The Netherlands into the sea. This is currently done using electric pumps. 

Efficiency

A 2012 study on efficiency from Yale university concluded that the highest extractable work in constant-pressure PRO with a seawater draw solution and river water feed solution is 0.75 kWh/m³ while the free energy of mixing is 0.81 kWh/m³—a thermodynamic extraction efficiency of 91.0%.

Methods

While the mechanics and concepts of salinity gradient power are still being studied, the power source has been implemented in several different locations. Most of these are experimental, but thus far they have been predominantly successful. The various companies that have utilized this power have also done so in many different ways as there are several concepts and processes that harness the power from salinity gradient. 

Pressure-retarded osmosis

Simple PRO power generation scheme

 

Osmotic Power Prototype at Tofte (Hurum), Norway

One method to utilize salinity gradient energy is called pressure-retarded osmosis. In this method, seawater is pumped into a pressure chamber that is at a pressure lower than the difference between the pressures of saline water and fresh water. Freshwater is also pumped into the pressure chamber through a membrane, which increase both the volume and pressure of the chamber. As the pressure differences are compensated, a turbine is spun, providing kinetic energy. This method is being specifically studied by the Norwegian utility Statkraft, which has calculated that up to 2.85 GW would be available from this process in Norway. Statkraft has built the world's first prototype PRO power plant on the Oslo fjord which was opened by Princess Mette-Marit of Norway on November 24, 2009. It aimed to produce enough electricity to light and heat a small town within five years by osmosis. At first, it did produce a minuscule 4 kilowatts – enough to heat a large electric kettle, but by 2015 the target was 25 megawatts – the same as a small wind farm. In January 2014 however Statkraft announced not to continue this pilot.

Reversed electrodialysis

A second method being developed and studied is reversed electrodialysis or reverse dialysis, which is essentially the creation of a salt battery. This method was described by Weinstein and Leitz as “an array of alternating anion and cation exchange membranes can be used to generate electric power from the free energy of river and sea water.”

The technology related to this type of power is still in its infant stages, even though the principle was discovered in the 1950s. Standards and a complete understanding of all the ways salinity gradients can be utilized are important goals to strive for in order make this clean energy source more viable in the future. 

Capacitive method

A third method is Doriano Brogioli's capacitive method, which is relatively new and has so far only been tested on lab scale. With this method energy can be extracted out of the mixing of saline water and freshwater by cyclically charging up electrodes in contact with saline water, followed by a discharge in freshwater. Since the amount of electrical energy which is needed during the charging step is less than one gets out during the discharge step, each completed cycle effectively produces energy. An intuitive explanation of this effect is that the great number of ions in the saline water efficiently neutralizes the charge on each electrode by forming a thin layer of opposite charge very close to the electrode surface, known as an electric double layer. Therefore, the voltage over the electrodes remains low during the charge step and charging is relatively easy. In between the charge and discharge step, the electrodes are brought in contact with freshwater. After this, there are less ions available to neutralize the charge on each electrode such that the voltage over the electrodes increases. The discharge step which follows is therefore able to deliver a relatively high amount of energy. A physical explanation is that on an electrically charged capacitor, there is a mutually attractive electric force between the electric charge on the electrode, and the ionic charge in the liquid. In order to pull ions away from the charged electrode, osmotic pressure must do work. This work done increases the electrical potential energy in the capacitor. An electronic explanation is that capacitance is a function of ion density. By introducing a salinity gradient and allowing some of the ions to diffuse out of the capacitor, this reduces the capacitance, and so the voltage must increase, since the voltage equals the ratio of charge to capacitance. 

Vapor pressure differences: open cycle and absorption refrigeration cycle (closed cycle)

Both of these methods do not rely on membranes, so filtration requirements are not as important as they are in the PRO & RED schemes. 

Open cycle

Similar to the open cycle in ocean thermal energy conversion (OTEC). The disadvantage of this cycle is the cumbersome problem of a large diameter turbine (75 meters +) operating at below atmospheric pressure to extract the power between the water with less salinity & the water with greater salinity. 

Absorption refrigeration cycle (closed cycle)

For the purpose of dehumidifying air, in a water-spray absorption refrigeration system, water vapor is dissolved into a deliquescent salt water mixture using osmotic power as an intermediary. The primary power source originates from a thermal difference, as part of a thermodynamic heat engine cycle.

Solar pond

At the Eddy Potash Mine in New Mexico, a technology called "salinity gradient solar pond" (SGSP) is being utilized to provide the energy needed by the mine. This method does not harness osmotic power, only solar power (see: solar pond). Sunlight reaching the bottom of the saltwater pond is absorbed as heat. The effect of natural convection, wherein "heat rises", is blocked using density differences between the three layers that make up the pond, in order to trap heat. The upper convection zone is the uppermost zone, followed by the stable gradient zone, then the bottom thermal zone. The stable gradient zone is the most important. The saltwater in this layer can not rise to the higher zone because the saltwater above has lower salinity and is therefore less-dense and more buoyant; and it can not sink to the lower level because that saltwater is denser. This middle zone, the stable gradient zone, effectively becomes an "insulator" for the bottom layer (although the main purpose is to block natural convection, since water is a poor insulator). This water from the lower layer, the storage zone, is pumped out and the heat is used to produce energy, usually by turbine in an organic Rankine cycle.

In theory a solar pond could be used to generate osmotic power if evaporation from solar heat is used to create a salinity gradient, and the potential energy in this salinity gradient is harnessed directly using one of the first three methods above, such as the capacitive method. 

Boron nitride nanotubes

A research team built an experimental system using boron nitride that produced much greater power than the Statkraft prototype. It used an impermeable and electrically insulating membrane that was pierced by a single boron nitride nanotube with an external diameter of a few dozen nanometers. With this membrane separating a salt water reservoir and a fresh water reservoir, the team measured the electric current passing through the membrane using two electrodes immersed in the fluid either side of the nanotube. 

The results showed the device was able to generate an electric current on the order of a nanoampere. The researchers claim this is 1,000 times the yield of other known techniques for harvesting osmotic energy and makes boron nitride nanotubes an extremely efficient solution for harvesting the energy of salinity gradients for usable electrical power.

The team claimed that a 1 square metre (11 sq ft) membrane could generate around 4 kW and be capable of generating up to 30 MWh per year.

At the 2019 fall meeting of the Materials Research Society a team from Rutgers University reported creating a membrane that contained around 10 million BNNTs per cubic centimeter.

Using low caloric waste energy by regenerate a high solution ammonium bicarbonate in a solution with a low salinity

At Pennsylvania State University, Dr. Logan tries to use waste heat with low calority using the fact that ammonium bicarbonate disappears into NH₃ and CO₂ in warm water to form ammonia bicarbonate again in cold water. So in a RED energy producing closed system the two different gradients of salinity are kept.

Possible negative environmental impact

Marine and river environments have obvious differences in water quality, namely salinity. Each species of aquatic plant and animal is adapted to survive in either marine, brackish, or freshwater environments. There are species that can tolerate both, but these species usually thrive best in a specific water environment. The main waste product of salinity gradient technology is brackish water. The discharge of brackish water into the surrounding waters, if done in large quantities and with any regularity, will cause salinity fluctuations. While some variation in salinity is usual, particularly where fresh water (rivers) empties into an ocean or sea anyway, these variations become less important for both bodies of water with the addition of brackish waste waters. Extreme salinity changes in an aquatic environment may result in findings of low densities of both animals and plants due to intolerance of sudden severe salinity drops or spikes. According to the prevailing environmentalist opinions, the possibility of these negative effects should be considered by the operators of future large blue energy establishments. 

The impact of brackish water on ecosystems can be minimized by pumping it out to sea and releasing it into the mid-layer, away from the surface and bottom ecosystems. 

Impingement and entrainment at intake structures are a concern due to large volumes of both river and sea water utilized in both PRO and RED schemes. Intake construction permits must meet strict environmental regulations and desalination plants and power plants that utilize surface water are sometimes involved with various local, state and federal agencies to obtain permission that can take upwards to 18 months.

Chemotaxis

From Wikipedia, the free encyclopedia

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

 

Capillary tube assay for chemotaxis. Motile prokaryotes sense chemicals in their environment and change their motility accordingly. Absent chemicals, movement is completely random. When an attractant or repellent is present, runs become longer and tumbles become less frequent. The result is net movement towards or away from the chemical (i.e., up or down the chemical gradient). The net movement can be seen in the beaker, where the bacteria accumulate around the origin of the attractant, and away from the origin of the repellent.

Chemotaxis (from chemo- + taxis) is the movement of an organism in response to a chemical stimulus. Somatic cells, bacteria, and other single-cell or multicellular organisms direct their movements according to certain chemicals in their environment. This is important for bacteria to find food (e.g., glucose) by swimming toward the highest concentration of food molecules, or to flee from poisons (e.g., phenol). In multicellular organisms, chemotaxis is critical to early development (e.g., movement of sperm towards the egg during fertilization) and subsequent phases of development (e.g., migration of neurons or lymphocytes) as well as in normal function and health (e.g., migration of leukocytes during injury or infection). In addition, it has been recognized that mechanisms that allow chemotaxis in animals can be subverted during cancer metastasis. The aberrant chemotaxis of leukocytes and lymphocytes also contribute to inflammatory diseases such as atherosclerosis, asthma, and arthritis.

Positive chemotaxis occurs if the movement is toward a higher concentration of the chemical in question; negative chemotaxis if the movement is in the opposite direction. Chemically prompted kinesis (randomly directed or nondirectional) can be called chemokinesis. 

History of chemotaxis research

Although migration of cells was detected from the early days of the development of microscopy by Leeuwenhoek, a Caltech lecture regarding chemotaxis propounds that 'erudite description of chemotaxis was only first made by T. W. Engelmann (1881) and W. F. Pfeffer (1884) in bacteria, and H. S. Jennings (1906) in ciliates'. The Nobel Prize laureate I. Metchnikoff also contributed to the study of the field during 1882 to 1886, with investigations of the process as an initial step of phagocytosis. The significance of chemotaxis in biology and clinical pathology was widely accepted in the 1930s, and the most fundamental definitions underlying the phenomenon were drafted by this time. The most important aspects in quality control of chemotaxis assays were described by H. Harris in the 1950s.^[10] In the 1960s and 1970s, the revolution of modern cell biology and biochemistry provided a series of novel techniques that became available to investigate the migratory responder cells and subcellular fractions responsible for chemotactic activity. The availability of this technology led to the discovery of C5a, a major chemotactic factor involved in acute inflammation. The pioneering works of J. Adler modernized Pfeffer's capillary assay and represented a significant turning point in understanding the whole process of intracellular signal transduction of bacteria.

Bacterial chemotaxis—general characteristics

Some bacteria, such as E. coli, have several flagella per cell (4–10 typically). These can rotate in two ways:

1. Counter-clockwise rotation aligns the flagella into a single rotating bundle, causing the bacterium to swim in a straight line; and
2. Clockwise rotation breaks the flagella bundle apart such that each flagellum points in a different direction, causing the bacterium to tumble in place.

The directions of rotation are given for an observer outside the cell looking down the flagella toward the cell.

Behavior

The overall movement of a bacterium is the result of alternating tumble and swim phases. As a result, the trajectory of a bacterium swimming in a uniform environment will form a random walk with relatively straight swims interrupted by random tumbles that reorient the bacterium. Bacteria such as E. coli are unable to choose the direction in which they swim, and are unable to swim in a straight line for more than a few seconds due to rotational diffusion; in other words, bacteria "forget" the direction in which they are going. By repeatedly evaluating their course, and adjusting if they are moving in the wrong direction, bacteria can direct their random walk motion toward favorable locations.

In the presence of a chemical gradient bacteria will chemotax, or direct their overall motion based on the gradient. If the bacterium senses that it is moving in the correct direction (toward attractant/away from repellent), it will keep swimming in a straight line for a longer time before tumbling; however, if it is moving in the wrong direction, it will tumble sooner and try a new direction at random. In other words, bacteria like E. coli use temporal sensing to decide whether their situation is improving or not, and in this way, find the location with the highest concentration of attractant (usually the source) quite well. Even under very high concentrations, it can still distinguish very small differences in concentration, and fleeing from a repellent works with the same efficiency.

This biased random walk is a result of simply choosing between two methods of random movement; namely tumbling and straight swimming. The helical nature of the individual flagellar filament is critical for this movement to occur. The protein structure that makes up the flagellar filament, flagellin, is conserved among all flagellated bacteria. Vertebrates seem to have taken advantage of this fact by possessing an immune receptor (TLR5) designed to recognize this conserved protein.

As in many instances in biology, there are bacteria that do not follow this rule. Many bacteria, such as Vibrio, are monoflagellated and have a single flagellum at one pole of the cell. Their method of chemotaxis is different. Others possess a single flagellum that is kept inside the cell wall. These bacteria move by spinning the whole cell, which is shaped like a corkscrew.

Signal transduction

Chemical gradients are sensed through multiple transmembrane receptors, called methyl-accepting chemotaxis proteins (MCPs), which vary in the molecules that they detect. Thousands of MCP receptors are known to be encoded across the bacterial kingdom. These receptors may bind attractants or repellents directly or indirectly through interaction with proteins of periplasmatic space. The signals from these receptors are transmitted across the plasma membrane into the cytosol, where Che proteins are activated. The Che proteins alter the tumbling frequency, and alter the receptors.

Flagellum regulation

The proteins CheW and CheA bind to the receptor. The absence of receptor activation results in autophosphorylation in the histidine kinase, CheA, at a single highly conserved histidine residue. CheA, in turn, transfers phosphoryl groups to conserved aspartate residues in the response regulators CheB and CheY; CheA is a histidine kinase and it does not actively transfer the phosphoryl group, rather, the response regulator CheB takes the phosphoryl group from CheA. This mechanism of signal transduction is called a two-component system, and it is a common form of signal transduction in bacteria. CheY induces tumbling by interacting with the flagellar switch protein FliM, inducing a change from counter-clockwise to clockwise rotation of the flagellum. Change in the rotation state of a single flagellum can disrupt the entire flagella bundle and cause a tumble.

Receptor regulation

CheB, when activated by CheA, acts as a methylesterase, removing methyl groups from glutamate residues on the cytosolic side of the receptor; it works antagonistically with CheR, a methyltransferase, which adds methyl residues to the same glutamate residues. If the level of an attractant remains high, the level of phosphorylation of CheA (and, therefore, CheY and CheB) will remain low, the cell will swim smoothly, and the level of methylation of the MCPs will increase (because CheB-P is not present to demethylate). The MCPs no longer respond to the attractant when they are fully methylated; therefore, even though the level of attractant might remain high, the level of CheA-P (and CheB-P) increases and the cell begins to tumble. The MCPs can be demethylated by CheB-P, and, when this happens, the receptors can once again respond to attractants. The situation is the opposite with regard to repellents: fully methylated MCPs respond best to repellents, while least-methylated MCPs respond worst to repellents. This regulation allows the bacterium to 'remember' chemical concentrations from the recent past, a few seconds, and compare them to those it is currently experiencing, thus 'know' whether it is traveling up or down a gradient. Although the methylation system accounts for the wide range of sensitivity that bacteria have to chemical gradients, other mechanisms are involved in increasing the absolute value of the sensitivity on a given background. Well-established examples are the ultra-sensitive response of the motor to the CheY-P signal, and the clustering of chemoreceptors.

Chemoattractants and chemorepellents

Chemoattractants and chemorepellents are inorganic or organic substances possessing chemotaxis-inducer effect in motile cells. These chemotactic ligands create chemical concentration gradients that organisms, prokaryotic and eukaryotic, move toward or away from, respectively.

Effects of chemoattractants are elicited via chemoreceptors such as methyl-accepting chemotaxis proteins (MCP). MCPs in E.coli include Tar, Tsr, Trg and Tap. Chemoattracttants to Trg include ribose and galactose with phenol as a chemorepellent. Tap and Tsr recognize dipeptides and serine as chemoattractants, respectively.

Chemoattractants or chemorepellents bind MCPs at its extracellular domain; an intracellular signaling domain relays the changes in concentration of these chemotactic ligands to downstream proteins like that of CheA which then relays this signal to flagellar motors via phosphorylated CheY (CheY-P). CheY-P can then control flagellar rotation influencing the direction of cell motility.

For E.coli, S. meliloti, and R. spheroids, the binding of chemoattractants to MCPs inhibit CheA and therefore CheY-P activity, resulting in smooth runs, but for B. substilis, CheA activity increases. Methylation events in E.coli cause MCPs to have lower affinity to chemoattractants which causes increased activity of CheA and CheY-P resulting in tumbles. In this way cells are able to adapt to the immediate chemoattractant concentration and detect further changes to modulate cell motility.

Chemoattractants in eukaryotes are well characterized for immune cells. Formyl peptides, such as fMLF, attract leukocytes such as neutrophils and macrophages, causing movement toward infection sites. Non-acylated methioninyl peptides do not act as chemoattractants to neutrophils and macrophages. Leukocytes also move toward chemoattractants C5a, a complement component, and pathogen-specific ligands on bacteria.

Mechanisms concerning chemorepellents are less known than chemoattractants. Although chemorepellents work to confer an avoidance response in organisms, Tetrahymena thermophila adapt to a chemorepellent, Netrin-1 peptide, within 10 minutes of exposure; however, exposure to chemorepellents such as GTP, PACAP-38, and nociceptin show no such adaptations. GTP and ATP are chemorepellents in micro-molar concentrations to both Tetrahymena and Paramecium. These organisms avoid these molecules by producing avoiding reactions to re-orient themselves away from the gradient.

Eukaryotic chemotaxis

The mechanism of chemotaxis that eukaryotic cells employ is quite different from that in bacteria; however, sensing of chemical gradients is still a crucial step in the process. Due to their small size, prokaryotes cannot directly detect a concentration gradient. Instead, prokaryotes sense their environments temporally, constantly swimming and redirecting themselves each time they sense a change in the gradient.

Eukaryotic cells are much larger than prokaryotes and have receptors embedded uniformly throughout the cell membrane. Eukaryotic chemotaxis involves detecting a concentration gradient spatially by comparing the asymmetric activation of these receptors at the different ends of the cell. Activation of these receptors results in migration towards chemoattractants, or away from chemorepellants.

It has also been shown that both prokaryotic and eukaryotic cells are capable of chemotactic memory. In prokaryotes, this mechanism involves the methylation of receptors called methyl-accepting chemotaxis proteins (MCPs). This results in their desensitization and allows prokaryotes to "remember" and adapt to a chemical gradient. In contrast, chemotactic memory in eukaryotes can be explained by the Local Excitation Global Inhibition (LEGI) model. LEGI involves the balance between a fast excitation and delayed inhibition which controls downstream signaling such as Ras activation and PIP3 production.

Levels of receptors, intracellular signalling pathways and the effector mechanisms all represent diverse, eukaryotic-type components. In eukaryotic unicellular cells, amoeboid movement and cilium or the eukaryotic flagellum are the main effectors (e.g., Amoeba or Tetrahymena). Some eukaryotic cells of higher vertebrate origin, such as immune cells also move to where they need to be. Besides immune competent cells (granulocyte, monocyte, lymphocyte) a large group of cells—considered previously to be fixed into tissues—are also motile in special physiological (e.g., mast cell, fibroblast, endothelial cells) or pathological conditions (e.g., metastases). Chemotaxis has high significance in the early phases of embryogenesis as development of germ layers is guided by gradients of signal molecules.

Motility

Unlike motility in bacterial chemotaxis, the mechanism by which eukaryotic cells physically move is unclear. There appear to be mechanisms by which an external chemotactic gradient is sensed and turned into an intracellular PIP3 gradient, which results in a gradient and the activation of a signaling pathway, culminating in the polymerisation of actin filaments. The growing distal end of actin filaments develops connections with the internal surface of the plasma membrane via different sets of peptides and results in the formation of anteriorpseudopods and posterior uropods. Cilia of eukaryotic cells can also produce chemotaxis; in this case, it is mainly a Ca²⁺-dependent induction of the microtubular system of the basal body and the beat of the 9 + 2 microtubules within cilia. The orchestrated beating of hundreds of cilia is synchronized by a submembranous system built between basal bodies. The details of the signaling pathways are still not totally clear. 

Chemotaxis-related migratory responses

Chemotaxis refers to the directional migration of cells in response to chemical gradients; several variations of chemical-induced migration exist as listed below.

• Chemokinesis refers to an increase in cellular motility in response to chemicals in the surrounding environment. Unlike chemotaxis, the migration stimulated by chemokinesis lacks directionality, and instead increases environmental scanning behaviors.
• In haptotaxis the gradient of the chemoattractant is expressed or bound on a surface, in contrast to the classical model of chemotaxis, in which the gradient develops in a soluble fluid. The most common biologically active haptotactic surface is the extracellular matrix (ECM); the presence of bound ligands is responsible for induction of transendothelial migration and angiogenesis.
• Necrotaxis embodies a special type of chemotaxis when the chemoattractant molecules are released from necrotic or apoptotic cells. Depending on the chemical character of released substances, necrotaxis can accumulate or repel cells, which underlines the pathophysiological significance of this phenomenon.

Receptors

In general, eukaryotic cells sense the presence of chemotactic stimuli through the use of 7-transmembrane (or serpentine) heterotrimeric G-protein-coupled receptors, a class representing a significant portion of the genome. Some members of this gene superfamily are used in eyesight (rhodopsins) as well as in olfaction (smelling). The main classes of chemotaxis receptors are triggered by:

• formyl peptides - formyl peptide receptors (FPR),
• chemokines - chemokine receptors (CCR or CXCR), and
• leukotrienes - leukotriene receptors (BLT).

However, induction of a wide set of membrane receptors (e.g., cyclic nucleotides, amino acids, insulin, vasoactive peptides) also elicit migration of the cell.

Chemotactic selection

While some chemotaxis receptors are expressed in the surface membrane with long-term characteristics, as they are determined genetically, others have short-term dynamics, as they are assembled ad hoc in the presence of the ligand. The diverse features of the chemotaxis receptors and ligands allows for the possibility of selecting chemotactic responder cells with a simple chemotaxis assay. By chemotactic selection, we can determine whether a still-uncharacterized molecule acts via the long- or the short-term receptor pathway. The term chemotactic selection is also used to designate a technique that separates eukaryotic or prokaryotic cells according to their chemotactic responsiveness to selector ligands.

Chemotactic ligands

The number of molecules capable of eliciting chemotactic responses is relatively high, and we can distinguish primary and secondary chemotactic molecules. The main groups of the primary ligands are as follows:

• Formyl peptides are di-, tri-, tetrapeptides of bacterial origin, formylated on the N-terminus of the peptide. They are released from bacteria in vivo or after decomposition of the cell[ a typical member of this group is the N-formylmethionyl-leucyl-phenylalanine (abbreviated fMLF or fMLP). Bacterial fMLF is a key component of inflammation has characteristic chemoattractant effects in neutrophil granulocytes and monocytes. The chemotactic factor ligands and receptors related to formyl peptides are summarized in the related article, Formyl peptide receptors.
• Complement 3a (C3a) and complement 5a (C5a) are intermediate products of the complement cascade. Their synthesis is joined to the three alternative pathways (classical, lectin-dependent, and alternative) of complement activation by a convertase enzyme. The main target cells of these derivatives are neutrophil granulocytes and monocytes as well.
• Chemokines belong to a special class of cytokines; not only do their groups (C, CC, CXC, CX₃C chemokines) represent structurally related molecules with a special arrangement of disulfide bridges but also their target cell specificity is diverse. CC chemokines act on monocytes (e.g., RANTES), and CXC chemokines are neutrophil granulocyte-specific (e.g., IL-8). Investigations of the three-dimensional structures of chemokines provided evidence that a characteristic composition of beta-sheets and an alpha helix provides expression of sequences required for interaction with the chemokine receptors. Formation of dimers and their increased biological activity was demonstrated by crystallography of several chemokines, e.g. IL-8.
• Metabolites of polyunsaturated fatty acids
  • Leukotrienes are eicosanoid lipid mediators made by the metabolism of arachidonic acid by ALOX5 (also termed 5-lipoxygenase). Their most prominent member with chemotactic factor activity is leukotriene B4, which elicits adhesion, chemotaxis, and aggregation of leukocytes. The chemoattractant action of LTB4 is induced via either of two G protein–coupled receptors, BLT1 and BLT2, which are highly expressed in cells involved in inflammation and allergy.
  • The family of 5-Hydroxyicosatetraenoic acid eicosanoids are arachidonic acid metabolites also formed by ALOX5. Three members of the family form naturally and have prominent chemotactic activity. These, listed in order of decreasing potency, are: 5-oxo-eicosatetraenoic acid, 5-oxo-15-hydroxy-eicosatetraenoic acid, and 5-Hydroxyeicosatetraenoic acid. This family of agonists stimulates chemotactic responses in human eosinophils, neutrophils, and monocytes by binding to the Oxoeicosanoid receptor 1, which like the receptors for leukotriene B4, is a G protein-coupled receptor. Aside from the skin, neutrophils are the body's first line of defense against bacterial infections. After leaving nearby blood vessels, these cells recognize chemicals produced by bacteria in a cut or scratch and migrate "toward the smell".
  • 5-hydroxyeicosatrieonic acid and 5-oxoeicosatrienoic acid are metabolites of Mead acid (5Z,8Z,11Z-eicosatrirenoid acid); they stimulate leukocyte chemotaxis through the oxoeicosanoid receptor 1^[55] with 5-oxoeicosatrienoic acid being as potent as its arachidonic acid-derived analog, 5-oxo-eicosatetraenoic acid, in stimulating human blood eosinophil and neutrophil chemotaxis.
  • 12-Hydroxyeicosatetraenoic acid is an eicosanoid metabolite of arachidonic acid made by ALOX12 which stimulates leukocyte chemotaxis through the leukotriene B4 receptor, BLT2.
  • Prostaglandin D2 is an eicosanoid metabolite of arachidononic acid made by cyclooxygenase 1 or cyclooxygenase 2 that stimulates chemotaxis through the Prostaglandin DP2 receptor. It elicits chemotactic responses in eosinophils, basophils, and T helper cells of the Th2 subtype.
  • 12-Hydroxyheptadecatrienoic acid is a non-eicosanoid metabolite of arachidonic acid made by cyclooxygenase 1 or cyclooxygenase 2 that stimulates leukocyte chemataxis though the leukotriene B4 receptor, BLT2.
  • 15-oxo-eicosatetraenoic acid is an eicosanoid metabolite of arachidonic acid made my ALOX15; it has weak chemotactic activity for human monocytes (sees 15-Hydroxyeicosatetraenoic acid#15-oxo-ETE). The receptor or other mechanism by which this metabolite stimulates chemotaxis has not been elucidated.

Chemotactic range fitting

Chemotactic responses elicited by the ligand-receptor interactions are, in general, distinguished upon the optimal effective concentration(s) of the ligand. Nevertheless, correlation of the amplitude elicited and ratio of the responder cells compared to the total number are also characteristic features of the chemotactic signaling. Investigations of ligand families (e.g., amino acids or oligo peptides) proved that there is a fitting of ranges (amplitudes; number of responder cells) and chemotactic activities: Chemoattractant moiety is accompanied by wide ranges, whereas chemorepellent character by narrow ranges. 

Clinical significance

A changed migratory potential of cells has relatively high importance in the development of several clinical symptoms and syndromes. Altered chemotactic activity of extracellular (e.g., Escherichia coli) or intracellular (e.g., Listeria monocytogenes) pathogens itself represents a significant clinical target. Modification of endogenous chemotactic ability of these microorganisms by pharmaceutical agents can decrease or inhibit the ratio of infections or spreading of infectious diseases. Apart from infections, there are some other diseases wherein impaired chemotaxis is the primary etiological factor, as in Chédiak–Higashi syndrome, where giant intracellular vesicles inhibit normal migration of cells.

Chemotaxis in diseases

Type of disease	Chemotaxis increased	Chemotaxis decreased
Infections	inflammations	AIDS, Brucellosis
Chemotaxis results the disease	—	Chédiak–Higashi syndrome, Kartagener syndrome
Chemotaxis is affected	atherosclerosis, arthritis, periodontitis, psoriasis, reperfusion injury, metastatic tumors	multiple sclerosis, Hodgkin disease, male infertility
Intoxications	asbestos, benzpyrene	Hg and Cr salts, ozone

Mathematical models

Several mathematical models of chemotaxis were developed depending on the type of

• migration (e.g., basic differences of bacterial swimming, movement of unicellular eukaryotes with cilia/flagellum and amoeboid migration)
• physico-chemical characteristics of the chemicals (e.g., diffusion) working as ligands
• biological characteristics of the ligands (attractant, neutral, and repellent molecules)
• assay systems applied to evaluate chemotaxis (see incubation times, development, and stability of concentration gradients)
• other environmental effects possessing direct or indirect influence on the migration (lighting, temperature, magnetic fields, etc.)

Although interactions of the factors listed above make the behavior of the solutions of mathematical models of chemotaxis rather complex, it is possible to describe the basic phenomenon of chemotaxis-driven motion in a straightforward way. Indeed, let us denote with ${\displaystyle \varphi }$ the spatially non-uniform concentration of the chemo-attractant and with ${\displaystyle \nabla \varphi }$ its gradient. Then the chemotactic cellular flow (also called current) ${\displaystyle J}$ that is generated by the chemotaxis is linked to the above gradient by the law: ${\displaystyle J=\chi C\nabla \varphi }$, where ${\displaystyle C}$ is the spatial density of the cells and ${\displaystyle \chi }$ is the so-called ’Chemotactic coefficient’. However, note that in many cases ${\displaystyle \chi }$ is not constant: It is, instead, a decreasing function of the concentration of the chemo-attractant ${\displaystyle \varphi }$: ${\displaystyle \chi (\varphi )}$. 

Spatial ecology of soil microorganisms is a function of their chemotactic sensitivities towards substrate and fellow organisms. The chemotactic behavior of the bacteria was proven to lead to non-trivial population patterns even in the absence of environmental heterogeneities. The presence of structural pore scale heterogeneities has an extra impact on the emerging bacterial patterns.

Measurement of chemotaxis

A wide range of techniques is available to evaluate chemotactic activity of cells or the chemoattractant and chemorepellent character of ligands. The basic requirements of the measurement are as follows:

• concentration gradients can develop relatively quickly and persist for a long time in the system
• chemotactic and chemokinetic activities are distinguished
• migration of cells is free toward and away on the axis of the concentration gradient
• detected responses are the results of active migration of cells

Despite the fact that an ideal chemotaxis assay is still not available, there are several protocols and pieces of equipment that offer good correspondence with the conditions described above. The most commonly used are summarised in the table below:

Type of assay	Agar-plate assays	Two-chamber assays	Others
Examples	PP-chamber	Boyden chamber Zigmond chamber Dunn chambers Multi-well chambers Capillary techniques	T-maze technique Opalescence technique Orientation assays

Artificial chemotactic systems

Chemical robots that use artificial chemotaxis to navigate autonomously have been designed. Applications include targeted delivery of drugs in the body. More recently, enzyme molecules have also shown positive chemotactic behavior in the gradient of their substrates. The thermodynamically-favorable binding of enzymes to their specific substrates is recognized as the origin of enzymatic chemotaxis. Additionally, enzymes in cascades have also shown substrate-driven chemotactic aggregation.

Apart from active enzymes, non-reacting molecules also show chemotactic behavior. This has been demonstrated by using dye molecules that move directionally in gradients of polymer solution through favorable hydrophobic interactions.

Information engineering (field)

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Information_engineering_(field)

Information engineering is the engineering discipline that deals with the generation, distribution, analysis, and use of information, data, and knowledge in systems. The field first became identifiable in the early 21st century.

Object detection for a stop sign.

 

The components of information engineering include more theoretical fields such as machine learning, artificial intelligence, control theory, signal processing, and information theory, and more applied fields such as computer vision, natural language processing, bioinformatics, medical image computing, cheminformatics, autonomous robotics, mobile robotics, and telecommunications. Many of these originate from computer science, as well as other branches of engineering such as computer engineering, electrical engineering, and bioengineering.

An example of clustering in machine learning.

The field of information engineering is based heavily on mathematics, particularly probability, statistics, calculus, linear algebra, optimization, differential equations, variational calculus, and complex analysis.

Information engineers often hold a degree in information engineering or a related area, and are often part of a professional body such as the Institution of Engineering and Technology or Institute of Measurement and Control. They are employed in almost all industries due to the widespread use of information engineering. 

History

The term information engineering used to refer to a software engineering methodology that is now more commonly known as information technology engineering or information engineering methodology. It began to gain its current meaning early on in the 21st century.

Elements

Machine learning and statistics

Machine learning is the field that involves the use of statistical and probabilistic methods to let computers "learn" from data without being explicitly programmed. Data science involves the application of machine learning to extract knowledge from data. 

Subfields of machine learning include deep learning, supervised learning, unsupervised learning, reinforcement learning, semi-supervised learning, and active learning. 

Causal inference is another related component of information engineering. 

Control theory

Control theory refers to the control of (continuous) dynamical systems, with the aim being to avoid delays, overshoots, or instability. Information engineers tend to focus more on control theory rather than the physical design of control systems and circuits (which tends to fall under electrical engineering). 

Subfields of control theory include classical control, optimal control, and nonlinear control. 

Signal processing

Signal processing refers to the generation, analysis and use of signals, which could take many forms such as image, sound, electrical, or biological.

An example of how the 2D Fourier transform can be used to remove unwanted information from an X-ray scan.

 

Information theory

Information theory studies the analysis, transmission, and storage of information. Major subfields of information theory include coding and data compression.

Computer vision

Computer vision is the field that deals with getting computers to understand image and video data at a high level.

Natural language processing

Natural language processing deals with getting computers to understand human (natural) languages at a high level. This usually means text, but also often includes speech processing and recognition.

Bioinformatics

Bioinformatics is the field that deals with the analysis, processing, and use of biological data. This usually means topics such as genomics and proteomics, and sometimes also includes medical image computing. 

Cheminformatics

Cheminformatics is the field that deals with the analysis, processing, and use of chemical data.

Robotics

Robotics in information engineering focuses mainly on the algorithms and computer programs used to control robots. As such, information engineering tends to focus more on autonomous, mobile, or probabilistic robots. Major subfields studied by information engineers include control, perception, SLAM, and motion planning.

Tools

In the past some areas in information engineering such as signal processing used analog electronics, but nowadays most information engineering is done with digital computers. Many tasks in information engineering can be parallelized, and so nowadays information engineering is carried out using CPUs, GPUs, and AI accelerators. There has also been interest in using quantum computers for some subfields of information engineering such as machine learning and robotics.