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Centrifugation

Centrifugation is a mechanical process which involves the use of the centrifugal force to separate particles from a solution according to their size, shape, density, medium viscosity and rotor speed. The denser components of the mixture migrate away from the axis of the centrifuge, while the less dense components of the mixture migrate towards the axis. Chemists and biologists may increase the effective gravitational force of the test tube so that the precipitate (pellet) will travel quickly and fully to the bottom of the tube. The remaining liquid that lies above the precipitate is called a supernatant or supernate.

There is a correlation between the size and density of a particle and the rate that the particle separates from a heterogeneous mixture, when the only force applied is that of gravity. The larger the size and the larger the density of the particles, the faster they separate from the mixture. By applying a larger effective gravitational force to the mixture, like a centrifuge does, the separation of the particles is accelerated. This is ideal in industrial and lab settings because particles that would naturally separate over a long period of time can be separated in much less time.

The rate of centrifugation is specified by the angular velocity usually expressed as revolutions per minute (RPM), or acceleration expressed as g. The conversion factor between RPM and g depends on the radius of the centrifuge rotor. The particles' settling velocity in centrifugation is a function of their size and shape, centrifugal acceleration, the volume fraction of solids present, the density difference between the particle and the liquid, and the viscosity. The most common application is the separation of solid from highly concentrated suspensions, which is used in the treatment of sewage sludges for dewatering where less consistent sediment is produced.

The centrifugation method has a wide variety of industrial and laboratorial applications; not only is this process used to separate two miscible substances, but also to analyze the hydrodynamic properties of macromolecules. It is one of the most important and commonly used research methods in biochemistry, cell and molecular biology. In the chemical and food industries, special centrifuges can process a continuous stream of particle turning into separated liquid like plasma. Centrifugation is also the most common method used for uranium enrichment, relying on the slight mass difference between atoms of U-238 and U-235 in uranium hexafluoride gas.

Mathematical formula
In a liquid suspension, many particles or cells will gradually fall to the bottom of the container due to gravity; however, the amount of time taken for such separations is not feasible. Other particles, which are very small, can not be isolated at all in solution until they are exposed to a high centrifugal force. As the suspension is rotated at a certain speed or revolutions per minute (RPM), the centrifugal force allows the particles to travel radially away from the rotation axis. The general formula for calculating the revolutions per minute (RPM) of a centrifuge is:

$$RPM= \sqrt{g \over r}$$,

where g represents the relative centrifugal force (RCF) and r the radius from the center of the rotor to a point in the sample.

However, depending on the centrifuge model used, the respective angle of the rotor and the radius may vary, thus the formula gets modified. For example, the Sorvall #SS-34 rotor has a maximum radius of 10.8 cm, so the formula becomes $RPM= 299\sqrt{g \over r}$, which can further simplify to $RPM = 91\sqrt{g}$.

When compared to gravity, the particle force is called the 'Relative Centrifugal Force' (RCF). It is the perpendicular force exerted on the contents of the rotor as a result of the rotation, always relative to the gravity of the Earth, which measures the strength of rotors of different types and sizes. For instance, the RCF of 1000 x g means that the centrifugal force is 1000 times stronger than the Earth's gravitational force. RCF is dependent on the speed of rotation in rpm and the distance of the particles from the center of rotation. The most common formula used for calculating RCF is:

$$RCF = 1.118 \times 10^{-5} \times r \times (rpm)^2$$,

where $1.118 \times 10^{-5}$ is a constant; r is the radius, expressed in centimetres, between the axis of rotation and a point in the sample; and rpm is the speed in revolutions per minute.

Historically, many separations have been carried out at the speed of 3000 rpm; a rough guide to the ‘g’ force exerted at this speed is to multiply the centrifugation radius by a factor of 10, so a radius of 160 mm gives approximately 1600 x g. This is a rather arbitrary approach, since the RCF applied is linearly dependent on the radius, so a 10% larger radius means that a 10% higher RCF is applied at the same speed. Roughly, the above formula can be simplified to $RCF = 10 \times r$, with an error of only 0.62%.

Microcentrifuges
Microcentrifuges are specially designed table-top models with light, small-volume rotors capable of very fast acceleration up to approximately 17,000 rpm. They are lightweight devices which are primarily used for short-time centrifugation of samples up to around 0.2–2.0 mL. However, due to their small scale, they are readily transportable and, if necessary, can be operated in a cold room. They can be refrigerated or not. The microcentrifuge is normally used in research laboratories where small samples of biological molecules, cells, or nuclei are required to be subjected to high RCF for relatively short time intervals. Microcentrifuges designed for high-speed operation can reach up to 35,000 rpm, giving RCF up to 30000×g, and are called high-speed microcentrifuges.

Low-speed centrifuges
Low-speed centrifuges are used to harvest chemical precipitates, intact cells (animal, plant and some microorganisms), nuclei, chloroplasts, large mitochondria and the larger plasma-membrane fragments. Density gradients for purifying cells are also run in these centrifuges. Swinging-bucket rotors tend to be used very widely because of the huge flexibility of sample size through the use of adaptors. These machines have maximum rotor speeds of less than 10 000 rpm and vary from small, bench-top to large, floor-standing centrifuges.

High-speed centrifuges
High-speed centrifuges are typically used to harvest microorganisms, viruses, mitochondria, lysosomes, peroxisomes and intact tubular Golgi membranes. The majority of the simple pelleting tasks are carried out in fixed angle rotors. Some density-gradient work for purifying cells and organelles can be carried out in swinging-bucket rotors, or in the case of Percoll gradients in fixed-angle rotors. High-speed or superspeed centrifuges can handle larger sample volumes, from a few tens of millilitres to several litres. Additionally, larger centrifuges can also reach higher angular velocities (around 30,000 rpm). The rotors may come with different adapters to hold various sizes of test tubes, bottles, or microtiter plates.

Ultracentrifugations
Ultracentrifugation makes use of high centrifugal force for studying properties of biological particles at exceptionally high speeds. Current ultracentrifuges can spin to as much as 150,000 rpm (equivalent to 1,000,000 x g). They are used to harvest all membrane vesicles derived from the plasma membrane, endoplasmic reticulum (ER) and Golgi membrane, endosomes, ribosomes, ribosomal subunits, plasmids, DNA, RNA and proteins in fixed-angle rotors. Compared to microcentrifuges or high-speed centrifuges, ultracentrifuges can isolate much smaller particles and, additionally, whilst microcentrifuges and supercentrifuges separate particles in batches (limited volumes of samples must be handled manually in test tubes or bottles), ultracentrifuges can separate molecules in batch or continuous flow systems.

Ultracentrifugation is employed for separation of macromolecules/ligand binding kinetic studies, separation of various lipoprotein fractions from plasma and deprotonisation of physiological fluids for amino acid analysis.

They are the most commonly used centrifuge for the density-gradient purification of all particles except cells, and, whilst swinging buckets have been traditionally used for this purpose, fixed-angle rotors and vertical rotors are also used, particularly for self-generated gradients and can improve the efficiency of separation greatly. There are two kinds of ultracentrifuges: the analytical and the preparative.

Analytical ultracentrifugation
Analytical ultracentrifugation (AUC) can be used for determination of the properties of macromolecules such as shape, mass, composition, and conformation. It is a commonly used biomolecular analysis technique used to evaluate sample purity, to characterize the assembly and disassembly mechanisms of biomolecular complexes, to determine subunit stoichiometries, to identify and characterize macromolecular conformational changes, and to calculate equilibrium constants and thermodynamic parameters for self-associating and hetero-associating systems. Analytical ultracentrifuges incorporate a scanning visible/ultraviolet light-based optical detection system for real-time monitoring of the sample’s progress during a spin.

Samples are centrifuged with a high-density solution such as sucrose, caesium chloride, or iodixanol. The high-density solution may be at a uniform concentration throughout the test tube ("cushion") or a varying concentration ("gradient"). Molecular properties can be modeled through sedimentation velocity analysis or sedimentation equilibrium analysis. During the run, the particle or molecules will migrate through the test tube at different speeds depending on their physical properties and the properties of the solution, and eventually form a pellet at the bottom of the tube, or bands at various heights.

Preparative ultracentrifugation
Preparative ultracentrifuges are often used for separating particles according to their densities, isolating and/or harvesting denser particles for collection in the pellet, and clarifying suspensions containing particles. Sometimes researchers also use preparative ultracentrifuges if they need the flexibility to change the type of rotor in the instrument. Preparative ultracentrifuges can be equipped with a wide range of different rotor types, which can spin samples of different numbers, at different angles, and at different speeds.

Fractionation process
In biological research, cell fractionation typically includes the isolation of cellular components while retaining the individual roles of each component. Generally, the cell sample is stored in a suspension which is:
 * Buffered—neutral pH, preventing damage to the structure of proteins including enzymes (which could affect ionic bonds)
 * Isotonic (of equal water potential)—this prevents water gain or loss by the organelles
 * Cool—reducing the overall activity of enzyme released later in the procedure

Centrifugation is the first step in most fractionations. Through low-speed centrifugation, cell debris may be removed, leaving a supernatant preserving the contents of the cell. Repeated centrifugation at progressively higher speeds will fractionate homogenates of cells into their components. In general, the smaller the subcellular component, the greater is the centrifugal force required to sediment it. The soluble fraction of any lysate can then be further separated into its constituents using a variety of methods.

Differential centrifugation
Differential centrifugation is the simplest method of fractionation by centrifugation, commonly used to separate organelles and membranes found in cells. Organelles generally differ from each other in density and in size, making the use of differential centrifugation, and centrifugation in general, possible. The organelles can then be identified by testing for indicators that are unique to the specific organelles. The most widely used application of this technique is to produce crude subcellular fractions from a tissue homogenate such as that from rat liver. Particles of different densities or sizes in a suspension are sedimented at different rates, with the larger and denser particles sedimenting faster. These sedimentation rates can be increased by using centrifugal force.

A suspension of cells is subjected to a series of increasing centrifugal force cycles to produce a series of pellets comprising cells with a declining sedimentation rate. Homogenate includes nuclei, mitochondria, lysosomes, peroxisomes, plasma membrane sheets and a broad range of vesicles derived from a number of intracellular membrane compartments and also from the plasma membrane, typically in a buffered medium.

Density gradient centrifugation
Density gradient centrifugation is known to be one of the most efficient methods for separating suspended particles, and is used both as a separation technique and as a method for measuring the density of particles or molecules in a mixture.

It is used to separate particles on the basis of size, shape, and density by using a medium of graded densities. During a relatively short or slow centrifugation, the particles are separated by size, with larger particles sedimenting farther than smaller ones. Over a long or fast centrifugation, particles travel to locations in the gradient where the density of the medium is the same as that of the particle density; (ρp – ρm) → 0. Therefore, a small, dense particle initially sediments less readily than a large, low density particle. The large particles reach their equilibrium density position early, while the small particles slowly migrate across the large particle zone and ultimately take up an equilibrium position deeper into the gradient.

A tube, after being centrifuged by this method, has particles in order of density based on height. The object or particle of interest will reside in the position within the tube corresponding to its density. Nevertheless, some non-ideal sedimentations are still possible when using this method. The first potential issue is the unwanted aggregation of particles, but this can occur in any centrifugation. The second possibility occurs when droplets of solution that contain particles sediment. This is more likely to occur when working with a solution that has a layer of suspension floating on a dense liquid, which in fact have little to no density gradient.

Other applications
A centrifuge can be used to isolate small quantities of solids retained in suspension from liquids, such as in the separation of chalk powder from water. In biological research, it can be used in the purification of mammalian cells, fractionation of subcellular organelles, fractionation of membrane vesicles, fractionation of macromolecules and macromolecular complexes, etc. Centrifugation is used in many different ways in the food industry. For example, in the dairy industry, it is typically used in the clarification and skimming of milk, extraction of cream, production and recovery of casein, cheese production, removing bacterial contaminants, etc. This processing technique is also used in the production of beverages, juices, coffee, tea, beer, wine, soy milk, oil and fat processing/recovery, cocoa butter, sugar production, etc. It is also used in the clarification and stabilization of wine.

In forensic and research laboratories, it can be used in the separation of urine and blood components. It also aids in separation of proteins using purification techniques such as salting out, e.g. ammonium sulfate precipitation. Centrifugation is also an important technique in waste treatment, being one of the most common processes used for sludge dewatering. This process also plays a role in cyclonic separation, where particles are separated from an air-flow without the use of filters. In a cyclone collector, air moves in a helical path. Particles with high inertia are separated by the centrifugal force whilst smaller particles continue with the air-flow.

Centrifuges have also been used to a small degree to isolate lighter-than-water compounds, such as oil. In such situations, the aqueous discharge is obtained at the opposite outlet from which solids with a specific gravity greater than one are the target substances for separation.

History
By 1923 Theodor Svedberg and his student H. Rinde had successfully analyzed large-grained sols in terms of their gravitational sedimentation. Sols consist of a substance evenly distributed in another substance, also known as a colloid. However, smaller grained sols, such as those containing gold, could not be analyzed. To investigate this problem Svedberg developed an analytical centrifuge, equipped with a photographic absorption system, which would exert a much greater centrifugal effect. In addition, he developed the theory necessary to measure molecular weight. During this time, Svedberg's attention shifted from gold to proteins.

By 1900, it had been generally accepted that proteins were composed of amino acids; however, whether proteins were colloids or macromolecules was still under debate. One protein being investigated at the time was hemoglobin. It was determined to have 712 carbon, 1,130 hydrogen, 243 oxygen, two sulfur atoms, and at least one iron atom. This gave hemoglobin a resulting weight of approximately 16,000 dalton (Da) but it was uncertain whether this value was a multiple of one or four (dependent upon the number of iron atoms present).

Through a series of experiments utilizing the sedimentation equilibrium technique, two important observations were made: hemoglobin has a molecular weight of 68,000 Da, suggesting that there are four iron atoms present rather than one, and that, no matter where the hemoglobin was isolated from, it had exactly the same molecular weight. How something of such a large molecular mass could be consistently found, regardless of where it was sampled from in the body, was unprecedented and favored the idea that proteins are macromolecules rather than colloids. In order to investigate this phenomenon, a centrifuge with even higher speeds was needed, and thus the ultracentrifuge was created to apply the theory of sedimentation-diffusion. The same molecular mass was determined, and the presence of a spreading boundary suggested that it was a single compact particle. Further application of centrifugation showed that under different conditions the large homogeneous particles could be broken down into discrete subunits. The development of centrifugation was a great advance in experimental protein science.

Linderstorm-Lang, in 1937, discovered that density gradient tubes could be used for density measurements. He discovered this when working with potato yellow-dwarf virus. This method was also used in Meselson and Stahl's famous experiment in which they proved that DNA replication is semi-conservative by using different isotopes of nitrogen. They used density gradient centrifugation to determine which isotope or isotopes of nitrogen were present in the DNA after cycles of replication.

title: Centrifugation


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AFRINIC

AFRINIC (African Network Information Centre) is the regional Internet registry (RIR) for Africa. Its headquarters are in Ebene, Mauritius.

Before AFRINIC was formed, IP addresses (IPv6 and IPv4) for Africa were distributed by the Asia-Pacific Network Information Centre (APNIC), the American Registry for Internet Numbers (ARIN), and the RIPE NCC. ICANN provisionally recognized AFRINIC on 11 October 2004. The registry became operational on 22 February 2005. ICANN gave it final recognition in April 2005 in its year.

Board of directors
AFRINIC consists of a nine-member Board of Directors. Six of the directors are elected to represent the different sub-regions, while two directors are elected to serve on the Board-based solely on competency as opposed to regional representation. The last seat on the Board is filled by the Chief Executive Officer.

Elections are held at each AFRNIC Annual General Meeting (AGMM), which is conducted around May/June every year. Voting takes place both on-site at these meetings and prior to the meeting via online voting.

Council of Elders
The AFRINIC Council of Elders consists of six former AFRINIC chairpersons.

They fulfill an advisory role and harness all their experience leading the organization as former Chairs.

The Members of the AFRINIC Council of Elders are:
 * 1) Dr. Nii N. Quaynor  (AFRINIC Board of Trustees Chair: 2001–2004)
 * 2) Mr. Pierre S. Dandjinou  (AFRINIC Chair: 2004–2008) Board Member: 2004-2010
 * 3) Dr. Viv Padayatchy (AFRINIC Chair: 2008–2011) - Board Member: - 2005-2011
 * 4) Mrs. Maimouna Ndeye Diop Diagne  (AFRINIC Chair: 2011–2012) - Board Member: 2010-2013
 * 5) Dr. Christian Bope

AFRINIC Staff
AFRINIC staff carries out the daily operations of the organization.

The Staff is structured in nine departments: CEO's Office, HR and Administration, Research and Innovation, Finance and Accounting, External Relations, Communication and Public Relations, Member Services, IT and Engineering, and Capacity Building. These divisions encompass all AFRINIC activities, including that of acting as a central source of information for Members.

AFRINIC's open policy development process also invites stakeholders interested in Internet number resources from around the world (but mostly the African region) to participate. These include representatives from governments, regulators, educators, media, the technical community, civil society, and other not-for-profit organizations.

Public Policy Meeting
Each year, AFRINIC conducts two public policy meetings. These give the community the chance to come together for policy development, information sharing, and networking. The first Public Policy Meeting of each year is known as the Africa Internet Summit (AIS), and the second is held as a standalone meeting. The meetings are held in various locations throughout Africa.

Controversies and scandals
AFRINIC has been at the center of several organizational controversies in the past five years.

Corruption
A former senior management member from AFRINIC, Ernest Byaruhanga, committed what is tagged to be Africa's greatest internet heist. In total, 4.1 million IP addresses were stolen. 2.3 million came from AFRINIC's “free pool” and a further 1.7 million were “legacy” IP addresses. They were worth around $87M, according to MyBroadband. IPv4 addresses, which were already reserved and in use by major organizations were effectively hijacked and sold. These reappropriated IP addresses were used to forward spam, breach data records, and compromise functioning websites. Dozens of South African-based companies and businesses were impacted. Education sectors and the Department of Defence were also hit, losing addresses worth approximately $5.3M.

Sexual harassment and bullying complaint
In March 2018, allegations were filed by the RIR's former head of external relations, Vymala Poligadu. She alleged that the Board chair, VC and the head of financial department had been actively plotting to get her fired from her position. She also alleged that one of the staff had been sexually harassed by Afrinic's former chair Sunday Folayan.

The internal report detailing Poligadu's accusations was then leaked onto the organization's discussion mailing list by an anonymous poster, writing in response to a complaint by another member about high staff turnover.

The independent Investigation Committee's (IC) report concluded that the allegations were false and the chair breached the NDA of Board members; Sunday Folayan quit after the Investigation Committee proved that he breached the signed NDA of AFRINIC Board members.

Afri Holdings Ltd & Others vs AFRINIC
In June 2020, AFRINIC was taken to court by one of the men whose name and company have been linked to the heist of the African Internet resources committed by a founding member of AFRINIC, Ernest Byaruhanga. In a notice sent to individuals and organizations that hold IP addresses in the African region, the then AFRINIC CEO Eddy Kayihura stated that an application for an interim injunction against AFRINIC was brought before the Commercial Division of the Supreme Court of Mauritius. The application was lodged by Afri Holdings Ltd, Netstyle A. Ltd, and Elad Cohen. Internet investigator Ron Guilmette has linked Netstyle and Cohen's e-mail address to suspicious activity in South Africa, caused by large chunks of South African Internet Protocol address space, worth millions of dollars on the open reseller market, being stolen by AFRINIC's ex-top senior executive Ernest Byaruhanga. Affected IP addresses included a block that belongs to Sasol, and blocks that appear to belong to Tredcor, Afrox, Woolworths, and SITA. Documents obtained in August 2019 also showed that Cohen is a director and shareholder of Afri Holdings Ltd.

Logic Web Inc vs AFRINIC
On 1 October 2021, Logic Web Inc initiated an application for an interim injunction against AFRINIC. LogicWeb Inc has received a 196.52.0.0/14 block under the registered name of "ITC", which is a made-up name for a fake corporate entity that never existed, and one that was invented by the ex-AFRINIC senior management Ernest Byaruhanga as a WHOIS cover story for his IP addresses famous heist. The 196.52.0.0/14 block was another one of AFRINIC's senior management's thefts from the free pool and one that was subsequently sold or gifted to the proprietor of LogicWeb, Inc. of New York, USA, i.e. a certain Mr. Chad Abizeid. Sometime after Mr. Chad Abizeid received the 196.52.0.0/14 block that was stolen by Ernest Byaruhanga, which is worth well over $5 million, Mr. Abizeid tried to sell off the entire thing at once. Before recently reclaiming the stolen Internet Resources, the ex-CEO AFRINIC CEO, Eddy Kayihura, has known about the misappropriated 196.52.0.0/14 block for quite some time without taking any actions of reclaiming it, in potential with corruption from Mr. Abizeid, similar to the AfriHoldings lawsuit case.

AFRINIC's scandal of committing the biggest Internet Resources heist, valued at more than 50 million dollars, is still affecting businesses operations that are struggling to recover from AFRINIC's attempts of concealing the gravity of the thefts by reclaiming the stolen IP resources, with little to no consideration of the consequences on the African Internet Connectivity. These businesses are now taking the matter to the Mauritius Courts by filing lawsuits against AFRINIC's management.

Cloud Innovation Ltd vs AFRINIC
AFRINIC has been in a feud with Cloud Innovation (CI) since July 2021, as it intended to revoke over 6 million IP addresses from the company backing the claim by stating a breach in policy. However, Afrinic's attempt to seize IP addresses currently under Cloud Innovation's domain backfired, as by bringing the issue directly to court, without an effort to de-escalate the matter, the RIR did not follow its own in-house policies.

As a result of the unfounded claims advanced by Afrinic, the Supreme Court of Mauritius ordered that Afrinic bank accounts be frozen, thereby crippling its operations. On July 15, due to court order, Afrinic restored CI's IP address blocks. However, the RIR's bank assets remained frozen until October 15, when they were granted the removal of the freezing order against AFRINIC in the Mauritius Court. The litigation is still ongoing.

With the amount of IP addresses involved and Cloud Innovation's large international customer base, this litigation is said to be potentially impacting a large majority of the Internet's connectivity and operations. Internet professionals all over the world have raised concerns about the possible consequences that would result from Cloud Innovation's membership being possibly terminated.

In 2022, Cloud Innovation won in court against AFRINIC, with a Supreme Court Judge ruling in favor of the plaintiff, CI, and against AFRINIC. The Supreme Court Judge concluded that the lawsuits were caused by the registry's dogged “determination… to terminate (the plaintiff’s) membership.” At the same time, the judge found no evidence of the lawsuits being indeed vexatious, asking how “in these circumstances… can it be held against the applicant […] that it resorted to the court to preserve its rights?”

Africa on Cloud (PTY) Ltd v Afrinic
An Injunction has been issued against AFRINIC's board's illegal attempt to extend Director's term, In particular, board seat number 6 is currently being held by Abdalla Omari. This seat was given to Mr. Omari through the passing of an illegal resolution to extend a board member's office without an election.

Crystal Web (Pty) Ltd v AFRINIC
An order has been granted to Crystal Web, one of resources member of AFRINIC, to suspend the CEO of AFRINIC, Eddy Mabano Kayihura, after he tried to censor the community discussion list of AFRINIC because a resource member had uncovered information linking the CEO with a known terrorist supporter, Furthermore, Eddy has been the subject of many controversial and corruptions allegations over the short 2 years since he was in the office,. During his tenure as CEO, nearly 50 lawsuits have been filed against AFRINIC, with AFRINIC having been sued by over 8 different parties, including internal parties.

Lawsuit by suspended CEO Kayihura Mabano Eddy against AFRINIC
In July 2022, Eddy Kayihura tried to bypass member-based elections by the ATU to appoint directors though the court, thereby violating the bottom-up process in which the RIR is built on and hampering the intended effect of the internet self-governance model.

Interfere with rule of law and its home nation's sovereignty
The other four RIRs sent a letter in the name of Number Resources Organization (NRO) to the Mauritius government requesting government recognition of AFRINIC's international status.

This letter was not received well by the global community, and Sander Steffan, one of the NRO's number council members, described such a move as "neo-colonialism".

A formal board member of AFRINIC, CTO of Liquid Labs, also sent a letter to the Mauritius government requesting that they not act on the NRO letter by stating "please disregard it in its entirety and that the legal process be allowed to play out as per the Mauritian legal system".

International media at large has also been against this letter with one media personality calling it "causing collateral damage". Another referenced such action as a top-down approach (contradicting to bottom-up approach RIR was founded on) and questioned why RIR resisted the ITU proposal to take them over in the immunity is what they want.

The NRO letter called Cloud Innovation a vexatious litigant, but a week later a judgment from the supreme court was delivered that specifically noted Cloud Innovation is not a vexatious litigant. The judgement criticized AFRINIC for trying to pervert the course of justice.

IPv4 exhaustion
In April 2017, AFRINIC became the last regional Internet registry to run down to its last /8 block of IPv4 addresses (102/8), thus triggering the final phase of its IPv4 exhaustion policy. As a result, AFRINIC then implemented a soft landing policy for allocating the last /8 to its users, in which, since Phase 2 of the exhaustion period (started in January 2020 ), each AFRINIC customer is eligible for just one final maximum allocation of a /22 block of IPv4 addresses until the block is exhausted.

AFRINIC training
AFRINIC conducts a number of training courses in a wide variety of locations around the region. These courses are designed to educate participants to proficiently configure, manage and administer their Internet services and infrastructure and to embrace current best practices.

WHOIS database
The AFRINIC WHOIS Database contains registration details of IP addresses and AS numbers originally allocated by AFRINIC. It shows the organizations that hold the resources, where the allocations were made, and contact details for the networks. The organizations that hold those resources are responsible for updating their information in the database. The database can be searched by using the web interface on the AFRINIC site or by directing your whois client to whois.afrinic.net (for example, whois -h whois.afrinic.net 196.1.0.0/24).

The AFRINIC membership
Major Internet Service Providers (ISPs), Internet exchange point (IXPs), governments and academic institutions.

Policy development process
AFRINIC's policies are developed by the membership and broader Internet community. The major media for policy development are the face-to-face Public Policy Meetings, which are held twice each year, and mailing list discussions.

Economies
AFRINIC's service region is divided into six sub-regions in Africa for statistic gathering purposes and for Board of Directors elections to ensure regional representation.

These sub-regions are: Northern, Western, Central, Eastern, Southern and the Indian Ocean.

AFRINIC's service region also includes several islands located in the Atlantic Ocean which are listed in the Western or Central African regions.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: AFRINIC


text:
Turacin

Turacin is a naturally occurring red pigment that is 6% copper complexed to uroporphyrin III. Arthur Herbert Church discovered turacin in 1869.

It is found only in the bird family Musophagidae, the turacos. Other birds derive their red coloration from carotenoids (bright and orange-reds) or phaeomelanins (rusty and brownish-reds).

It is often assumed that this coloration will wash out when the birds are bathing or after heavy rains, but this is true only if the water used for bathing happens to be very alkaline.

The copper(II) uroporphyrin III pigment in turaco feathers was studied using electron spin resonance by Jack Peisach first with Blumberg and later with Mims.

title: Turacin