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The Silkie (also known as the Silky or Chinese silk chicken) is a breed of chicken named for its atypically fluffy plumage, which is said to feel like silk and satin. The breed has several other unusual qualities, such as black skin and bones, blue earlobes, and five toes on each foot, whereas most chickens only have four. They are often exhibited in poultry shows, and also appear in various colors. In addition to their distinctive physical characteristics, Silkies are well known for their calm, friendly temperament. It is among the most docile of poultry. Hens are also exceptionally broody, and care for young well. Although they are fair layers themselves, laying only about three eggs a week, they are commonly used to hatch eggs from other breeds and bird species due to their broody nature.

This is a list of present-day cities by the time period over which they have been continuously inhabited as a city. The age claims listed are generally disputed. Differences in opinion can result from different definitions of "city" as well as "continuous habitation" and historical evidence is often disputed. Caveats (and sources) to the validity of each claim are discussed in the "Notes" column.

The Vulcan salutation is a hand gesture popularized by the 1960s television series Star Trek. It consists of a raised hand with the palm forward and the thumb extended, while the fingers are parted between the middle and ring finger.

PhotoDNA is a proprietary image-identification and content filtering technology widely used by online service providers.

Heat-assisted magnetic recording (HAMR) is a magnetic storage technology for greatly increasing the amount of data that can be stored on a magnetic device such as a hard disk drive by temporarily heating the disk material during writing, which makes it much more receptive to magnetic effects and allows writing to much smaller regions (and much higher levels of data on a disk).

The technology was initially seen as extremely difficult to achieve, with doubts expressed about its feasibility in 2013. The regions being written must be heated in a tiny area - small enough that diffraction prevents the use of normal laser focused heating - and requires a heating, writing and cooling cycle of less than 1 nanosecond, while also controlling the effects of repeated spot-heating on the drive platters, the drive-to-head contact, and the adjacent magnetic data which must not be affected. These challenges required the development of nano-scale surface plasmons (surface guided laser) instead of direct laser-based heating, new types of glass platters and heat-control coatings that tolerate rapid spot-heating without affecting the contact with the recording head or nearby data, new methods to mount the heating laser onto the drive head, and a wide range of other technical, development and control issues that needed to be overcome.

In February 2019, Seagate Technology announced that HAMR would be launched commercially in 2019, having been extensively tested at partners during 2017 and 2018. The first drives will be 16 TB, with 20 TB expected in 2020, 24 TB drives in advanced development, and 40 TB drives by around 2023. Its planned successor, known as heated-dot magnetic recording (HDMR), or bit-pattern recording, is also under development, although not expected to be available until at least 2025 or later. HAMR drives have the same form factor (size and layout) as existing traditional hard drives, and do not require any change to the computer or other device in which they are installed; they can be used identically to existing hard drives. HAMR is expected to be delayed commercially until 2022, with 10-platter hard drives using perpendicular recording (expected to be followed by SMR) being used as a stopgap solution.

The Up series of documentary films follows the lives of ten males and four females in England beginning in 1964, when they were seven years old. The first film was titled Seven Up!, with later films adjusting the number in the title to match the age of the subjects at the time of filming. The documentary has had nine episodes—one every seven years—thus spanning 56 years. The series has been produced by Granada Television for ITV, which has broadcast all of them except 42 Up (1998), which was broadcast on BBC One. Individual films and the series as a whole have received numerous accolades; in 1991, the then-latest instalment, 28 Up, was chosen for Roger Ebert's list of the ten greatest films of all time.

The children were selected for the original programme to represent the range of socio-economic backgrounds in Britain at that time, with the expectation that each child's social class would determine their future. The first instalment was made as a one-off edition of Granada Television's series, World in Action, directed by Canadian Paul Almond, with involvement by "a fresh-faced young researcher, a middle-class Cambridge graduate", Michael Apted, whose role in the initial programme included "trawling the nation's schools for 14 suitable subjects". About the first programme, Apted has said:

It was Paul's film ... but he was more interested in making a beautiful film about being seven, whereas I wanted to make a nasty piece of work about these kids who have it all, and these other kids who have nothing.

After Almond's direction of the original programme, director Michael Apted continued the series with new instalments every seven years, filming material from those of the fourteen who chose to participate. The aim of the continuing series is stated at the beginning of 7 Up as: "Why did we bring these together? Because we wanted a glimpse of England in the year 2000. The union leader and the business executive of the year 2000 are now seven years old." The most recent instalment, the ninth, titled 63 Up, premiered in the UK on ITV in 2019. A special episode featuring celebrity fans of the series, 7 Up & Me, also aired on ITV in 2019. Apted is reported to have said, "I hope to do 84 Up when I'll be 99"; however, he died in 2021.

The Delphi method or Delphi technique ( DEL-fy; also known as Estimate-Talk-Estimate or ETE) is a structured communication technique or method, originally developed as a systematic, interactive forecasting method which relies on a panel of experts. The technique can also be adapted for use in face-to-face meetings, and is then called mini-Delphi or Estimate-Talk-Estimate (ETE). Delphi has been widely used for business forecasting and has certain advantages over another structured forecasting approach, prediction markets.

Delphi is based on the principle that forecasts (or decisions) from a structured group of individuals are more accurate than those from unstructured groups. The experts answer questionnaires in two or more rounds. After each round, a facilitator or change agent provides an anonymised summary of the experts' forecasts from the previous round as well as the reasons they provided for their judgments. Thus, experts are encouraged to revise their earlier answers in light of the replies of other members of their panel. It is believed that during this process the range of the answers will decrease and the group will converge towards the "correct" answer. Finally, the process is stopped after a predefined stop criterion (e.g., number of rounds, achievement of consensus, stability of results), and the mean or median scores of the final rounds determine the results.

Special attention has to be paid to the formulation of the Delphi theses and the definition and selection of the experts in order to avoid methodological weaknesses that severely threaten the validity and reliability of the results.

In linear algebra, the singular value decomposition (SVD) is a factorization of a real or complex matrix that generalizes the eigendecomposition of a square normal matrix to any ${\displaystyle m\times n}$ matrix via an extension of the polar decomposition.

Specifically, the singular value decomposition of an ${\displaystyle m\times n}$ real or complex matrix ${\displaystyle \mathbf {M} }$ is a factorization of the form ${\displaystyle \mathbf {U\Sigma V^{*}} }$, where ${\displaystyle \mathbf {U} }$ is an ${\displaystyle m\times m}$ real or complex unitary matrix, ${\displaystyle \mathbf {\Sigma } }$ is an ${\displaystyle m\times n}$ rectangular diagonal matrix with non-negative real numbers on the diagonal, and ${\displaystyle \mathbf {V} }$ is an ${\displaystyle n\times n}$ real or complex unitary matrix. If ${\displaystyle \mathbf {M} }$ is real, ${\displaystyle \mathbf {U} }$ and ${\displaystyle \mathbf {V} =\mathbf {V^{*}} }$ are real orthonormal matrices.

The diagonal entries ${\displaystyle \sigma _{i}=\Sigma _{ii}}$ of ${\displaystyle \mathbf {\Sigma } }$ are known as the singular values of ${\displaystyle \mathbf {M} }$. The number of non-zero singular values is equal to the rank of ${\displaystyle \mathbf {M} }$. The columns of ${\displaystyle \mathbf {U} }$ and the columns of ${\displaystyle \mathbf {V} }$ are called the left-singular vectors and right-singular vectors of ${\displaystyle \mathbf {M} }$, respectively.

The SVD is not unique. It is always possible to choose the decomposition so that the singular values ${\displaystyle \Sigma _{ii}}$are in descending order. In this case, Σ (but not always U and V) is uniquely determined by M.

The term sometimes refers to the compact SVD, a similar decomposition ${\displaystyle \mathbf {M} =\mathbf {U\Sigma V^{*}} }$ in which Σ is square diagonal of size ${\displaystyle r\times r}$, where ${\displaystyle r\leq \min\{m,n\}}$ is the rank of M, and has only the non-zero singular values. In this variant, ${\displaystyle \mathbf {U} }$ is an ${\displaystyle m\times r}$ matrix and ${\displaystyle \mathbf {V} }$ is an ${\displaystyle n\times r}$ matrix, such that ${\displaystyle \mathbf {U^{*}U} =\mathbf {V^{*}V} =\mathbf {I} _{r\times r}}$.

Mathematical applications of the SVD include computing the pseudoinverse, matrix approximation, and determining the rank, range, and null space of a matrix. The SVD is also extremely useful in all areas of science, engineering, and statistics, such as signal processing, least squares fitting of data, and process control.

The bus factor is a measurement of the risk resulting from information and capabilities not being shared among team members, derived from the phrase "in case they get hit by a bus." It is also known as the bread truck scenario, lottery factor, truck factor, bus/truck number, or lorry factor.

The concept is similar to the much older idea of key person risk, but considers the consequences of losing key technical experts, versus financial or managerial executives (who are theoretically replaceable at an insurable cost). Personnel must be both key and irreplaceable to contribute to the bus factor; losing a replaceable or non-key person would not result in a bus-factor effect.

The term was first applied to software development, where a team member might create critical components by crafting code that performs well, but which also is unavailable to other team members, such as work that was undocumented, never shared, encrypted, obfuscated, unpublished, or otherwise incomprehensible to others. Thus a key component would be effectively lost as a direct consequence of the absence of that team member, making the member key. If this component was key to the project's advancement, the project would stall.