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Shingled Magnetic Recording
Shingled magnetic recording (SMR) is a magnetic storage data recording technology used in hard disk drives (HDDs) to increase storage density and overall per-drive storage capacity. Conventional hard disk drives record data by writing non-overlapping magnetic tracks parallel to each other (perpendicular magnetic recording, PMR), while shingled recording writes new tracks that overlap part of the previously written magnetic track, leaving the previous track narrower and allowing for higher track density. Thus, the tracks partially overlap similar to roof shingles. This approach was selected because, if the writing head is made too narrow, it cannot provide the very high fields required in the recording layer of the disk.:7–9 The overlapping-tracks architecture complicates the writing process since writing to one track also overwrites an adjacent track. If adjacent tracks contain valid data, they must be rewritten as well. As a result, SMR drives are divided into many append-only (sequential) zones of overlapping tracks that need to be rewritten entirely when full, resembling flash blocks in solid state drives. Device-managed SMR devices hide this complexity by managing it in the firmware, presenting an interface like any other hard disk. Other SMR devices are host-managed and depend on the operating system to know how to handle the drive, and only write sequentially to certain regions of the drive. :11 ff. While SMR drives can use DRAM and flash memory caches to improve writing performance, continuous writing of large amount of data is noticeably slower than with PMR drives.
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  • 01 Dec 2022
Topic Review
Ionocraft
An ionocraft or ion-propelled aircraft (commonly known as a lifter or hexalifter) is a device that uses an electrical electrohydrodynamic (EHD) phenomenon to produce thrust in the air without requiring any combustion or moving parts. The term "ionocraft" dates back to the 1960s, an era in which EHD experiments were at their peak. In its basic form, it simply consists of two parallel conductive electrodes, one in the form of a fine wire and another which may be formed out of wire grid, tubes or foil skirts with a smooth round surface. When such an arrangement is powered by high voltage (in the range of a few kilovolts), it produces thrust. The ionocraft forms part of the EHD thruster family, but is a special case in which the ionisation and accelerating stages are combined into a single stage. The device is a popular science fair project for students. It is also popular among anti-gravity or so-called "electrogravitics" proponents, due to the research of Thomas Townsend Brown, who built these devices in the 1920s and incorrectly believed that he had found a way to modify gravity using electric fields. The term "lifter" is an accurate description because it is not an anti-gravity device; rather, it produces lift using the same basic principle as a rocket, i.e. from the equal but opposite force upward generated by the driving force downward, specifically by driving the ionized air downward in the case of the ionocraft. Much like a rocket or a jet engine (it can actually be much more thrust efficient than a jet engine), the force that an ionocraft generates is consistently oriented along its own axis, regardless of the surrounding gravitational field. Claims of the device also working in a vacuum have been disproved. Ionocraft require many safety precautions due to the high voltage required for their operation; nevertheless, a large subculture has grown up around this simple EHD thrusting device and its physics are now known to a much better extent.
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  • 01 Dec 2022
Topic Review
Phthalocyanine Blue BN
Phthalocyanine Blue BN, also called by many names (EINECS 205-685-1), is a bright, crystalline, synthetic blue pigment from the group of phthalocyanine dyes. Its brilliant blue is frequently used in paints and dyes. It is highly valued for its superior properties such as light fastness, tinting strength, covering power and resistance to the effects of alkalis and acids. It has the appearance of a blue powder, insoluble in most solvents including water.
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  • 01 Dec 2022
Topic Review
Virtual Synchrony
Virtual synchrony is an interprocess message passing (sometimes called ordered, reliable multicast) technology. Virtual synchrony systems allow programs running in a network to organize themselves into process groups, and to send messages to groups (as opposed to sending them to specific processes). Each message is delivered to all the group members, in the identical order, and this is true even when two messages are transmitted simultaneously by different senders. Application design and implementation is greatly simplified by this property: every group member sees the same events (group membership changes and incoming messages) in the same order. A virtually synchronous service is typically implemented using a style of programming called state machine replication, in which a service is first implemented using a single program that receives inputs from clients through some form of remote message passing infrastructure, then enters a new state and responds in a deterministic manner. The initial implementation is then transformed so that multiple instances of the program can be launched on different machines, using a virtually synchronous message passing system to replicate the incoming messages over the members. The replicas will see the same events in the same order, and are in the same states, hence they will make the same state transitions and remain in a consistent state. The replication of the service provides a form of fault-tolerance: if a replica fails (by crashing), the others remain and can continue to provide responses. Different members of the replica group can also be programmed to subdivide the workload, typically by using the group membership to determine their respective roles. This permits a group of N members to run as much as N times faster than a single member, or to handle N times as many requests, while continuing to offer fault-tolerance in the event of a crash. Virtual synchrony is distinguished from classical state machine replication because the model includes features whereby a programmer can request early (optimistic) delivery of messages, or relaxed forms of ordering. When used appropriately, these features can enable substantial speedup. However, the programmer needs to be sure that the relaxation of guarantees will not compromise correctness. For example, in a service that uses locking to protect concurrently updated data, the messaging system can be instructed to use an inexpensive form of message ordering, in which the messaging system respects the ordering in which individual senders send messages (FIFO guarantee) but does not attempt to impose an agreed order if messages are sent concurrently by different senders. Provided that the sender indeed held locks on the data, it can be shown that FIFO ordering suffices for correctness. The benefit is that FIFO ordering is much less costly to implement than total ordering for concurrent messages. To give another example, by delivering messages optimistically, virtual synchrony systems can outperform the Paxos that is normally required for implementation of state machine replication: Paxos normally requires a 2-phase protocol, whereas optimistic virtual synchrony protocols can deliver messages immediately upon their arrival. However, this could result in a violation of the safety property of the state machine replication model. To prevent such problems, the programmer who uses this feature is required to invoke a primitive called flush, which delays the caller until any optimistically delivered messages have reached all of the group members. Provided that the programmer understands this behavior and is careful to call flush before interacting with external clients or persistent storage, higher performance can be achieved without loss of safety. The flexibility associated with these limited forms of event reordering and optimistic early delivery permit virtual synchrony platforms to achieve extremely high data rates while still preserving very strong fault-tolerance and consistency guarantees.
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  • 01 Dec 2022
Topic Review
Contract (Canon Law)
The canon law of contract follows that of the civil jurisdiction in which canon law operates. (Latin contractus; Old French contract; Modern French contrat; Italian contratto).
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  • 01 Dec 2022
Topic Review
Air Source Heat Pumps
An air source heat pump (ASHP) is a system that transfers heat from outside to inside a building, or vice versa. Under the principles of vapor compression refrigeration, an ASHP uses a refrigerant system involving a compressor and a condenser to absorb heat at one place and release it at another. They can be used as a space heater or cooler, and are sometimes called "reverse-cycle air conditioners". In domestic heating use, an ASHP absorbs heat from outside air and releases it inside the building, as hot air, hot water-filled radiators, underfloor heating and/or domestic hot water supply. The same system can often do the reverse in summer, cooling the inside of the house. When correctly specified, an ASHP can offer a full central heating solution and domestic hot water up to 80 °C.
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  • 01 Dec 2022
Topic Review
Completion (Algebra)
In abstract algebra, a completion is any of several related functors on rings and modules that result in complete topological rings and modules. Completion is similar to localization, and together they are among the most basic tools in analysing commutative rings. Complete commutative rings have a simpler structure than general ones, and Hensel's lemma applies to them. In algebraic geometry, a completion of a ring of functions R on a space X concentrates on a formal neighborhood of a point of X: heuristically, this is a neighborhood so small that all Taylor series centered at the point are convergent. An algebraic completion is constructed in a manner analogous to completion of a metric space with Cauchy sequences, and agrees with it in case R has a metric given by a non-Archimedean absolute value.
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  • 01 Dec 2022
Topic Review
ITER
International Thermonuclear Experimental Reactor is an international nuclear fusion research and engineering megaproject, which will be the world's largest magnetic confinement plasma physics experiment. It is an experimental tokamak nuclear fusion reactor that is being built next to the Cadarache facility in Saint-Paul-lès-Durance, in Provence, southern France. The ITER thermonuclear fusion reactor has been designed to produce a fusion plasma equivalent to 500 megawatts (MW) of thermal output power for around twenty minutes while 50 megawatts of thermal power are injected into the tokamak, resulting in a ten-fold gain of plasma heating power. Thereby the machine aims to demonstrate the principle of producing more thermal power from the fusion process than is used to heat the plasma, something that has not yet been achieved in any fusion reactor. The total electricity consumed by the reactor and facilities will range from 110 MW up to 620 MW peak for 30-second periods during plasma operation. Thermal-to-electric conversion is not included in the design because ITER will not produce sufficient power for net electrical production. The emitted heat from the fusion reaction will be vented to the atmosphere. The project is funded and run by seven member entities—the European Union, India , Japan , China , Russia , South Korea and the United States . The EU, as host party for the ITER complex, is contributing about 45 percent of the cost, with the other six parties contributing approximately 9 percent each. In 2016 the ITER organization signed a technical cooperation agreement with the national nuclear fusion agency of Australia , granting this country access to research results of ITER in exchange for construction of selected parts of the ITER machine. Construction of the ITER Tokamak complex started in 2013 and the building costs were over US$14 billion by June 2015. The construction of the facility is expected to be completed in 2025 when commissioning of the reactor can commence. Initial plasma experiments are scheduled to begin in 2025, with full deuterium–tritium fusion experiments starting in 2035. If ITER becomes operational, it will become the largest magnetic confinement plasma physics experiment in use with a plasma volume of 840 cubic meters, surpassing the Joint European Torus by almost a factor of 10. The goal of ITER is to demonstrate the scientific and technological feasibility of fusion energy for peaceful use. It is the largest of more than 100 fusion reactors built since the 1950s. ITER's planned successor, DEMO, is expected to be the first fusion reactor to produce electricity in an experimental environment. DEMO's anticipated success is expected to lead to full-scale electricity-producing fusion power stations and future commercial reactors.
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  • 01 Dec 2022
Topic Review
Forensic Podiatry
Forensic Podiatry is a subdiscipline of forensic science in which specialized podiatric knowledge including foot and lower limb anatomy, musculoskeletal function, deformities and diseases of the foot, ankle, lower extremities, and at times, the entire human body is used in the examination of foot-related evidence in the context of a criminal investigation. Forensic Podiatry has been defined as: The application of sound and researched podiatry knowledge and experience in forensic investigations, to show the association of an individual with a scene of crime, or to answer any other legal question concerned with the foot or footwear that requires knowledge of the functioning foot. Those who specialize in this field need to have gained knowledge and experience in podiatry and also in forensic science and practice. Forensic Podiatry is usually used to assist in the process of human identification, but can also be employed to help address issues relating to questions that have arisen within the context of forensic enquiry. Such questions could include whether or not a shoe could have had multiple wearers, what the effects of a shoe not fitting correctly could have been, whether or not someone could have placed their foot into a shoe that was too small for the postulated wearer's foot and other matters involving the podiatric interpretation of relevant evidential materials.
  • 1.9K
  • 01 Dec 2022
Topic Review
μ-Recursive Function
In mathematical logic and computer science, the general recursive functions (often shortened to recursive functions) or μ-recursive functions are a class of partial functions from natural numbers to natural numbers that are "computable" in an intuitive sense. In computability theory, it is shown that the μ-recursive functions are precisely the functions that can be computed by Turing machines(this is one of the theorems that supports the Church–Turing thesis). The μ-recursive functions are closely related to primitive recursive functions, and their inductive definition (below) builds upon that of the primitive recursive functions. However, not every μ-recursive function is a primitive recursive function—the most famous example is the Ackermann function. Other equivalent classes of functions are the λ-recursive functions and the functions that can be computed by Markov algorithms. The subset of all total recursive functions with values in {0,1} is known in computational complexity theory as the complexity class R.
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  • 01 Dec 2022
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