In computing, particularly in the context of the Unix operating system and its workalikes, fork is an operation whereby a process creates a copy of itself. It is usually a system call, implemented in the kernel. Fork is the primary (and historically, only) method of process creation on Unix-like operating systems.
In multitasking operating systems, processes (running programs) need a way to create new processes, e.g. to run other programs. Fork and its variants are typically the only way of doing so in Unix-like systems. For a process to start the execution of a different program, it first forks to create a copy of itself. Then, the copy, called the "child process", calls the exec system call to overlay itself with the other program: it ceases execution of its former program in favor of the other.
In Unix systems equipped with virtual memory support (practically all modern variants), the fork operation creates a separate address space for the child. The child process has an exact copy of all the memory segments of the parent process, though if copy-on-write semantics are implemented, the physical memory need not be actually copied. Instead, virtual memory pages in both processes may refer to the same pages of physical memory until one of them writes to such a page: then it is copied. This optimization is important in the common case where fork is used in conjunction with exec to execute a new program: typically, the child process performs only a small set of actions before it ceases execution of its program in favour of the program to be started, and it requires very few, if any, of its parent's data structures.
A clone is a group of identical cells that share a common ancestry, meaning they are derived from the same cell.
Clonality implies the state of a cell or a substance being derived from one source or the other. Thus there are terms like polyclonal—derived from many clones; oligoclonal—derived from a few clones; and monoclonal—derived from one clone. These terms are most commonly used in context of antibodies or immunocytes.
This concept of clone assumes importance as all the cells that form a clone share common ancestry, which has a very significant consequence: shared genotype.
The process of immunological B-cell maturation involves transformation from an undifferentiated B cell to one that secretes antibodies with particular specificity. This differentiation and activation of the B cell occurs most rapidly after exposure to antigen by antigen-presenting cells in the reticuloendothelial system, and under modulation by T cells, and is closely intertwined with affinity maturation. B cells that respond most avidly to antigen are preferentially allowed to proliferate and mature, a process known as clonal selection.
In lymphocytic neoplastic diseases such as multiple myeloma and lymphoma, but also other illnesses, there can be a massive expansion of a single B-cell clone, detectable by measuring the excessively-produced antibodies, measured in a serum protein electrophoresis test or peripheral blood flow cytometry. Such an expansion is said to be "monoclonal", and monoclonal antibodies produced by such a group of B cells can cause illnesses such as amyloidosis and lupus, or can be indicative of an underlying malignancy. The concept of clonality is closely associated with malignancy, for example in diagnosing lymphomatoid skin lesions. The expansion of a particular clone of immune B cells is usually interpreted by clinicians as evidence of unrestricted cell growth, the hallmark of cancer.
A system is a set of interacting or interdependent component parts forming a complex/intricate whole. Every system is delineated by its spatial and temporal boundaries, surrounded and influenced by its environment, described by its structure and purpose and expressed in its functioning.
The term system may also refer to a set of rules that governs structure and/or behavior. Alternatively, and usually in the context of complex social systems, the term is used to describe the set of rules that govern structure and/or behavior.
The term "system" comes from the Latin word systēma, in turn from Greek σύστημα systēma: "whole compounded of several parts or members, system", literary "composition".
According to Marshall McLuhan,
"System" means "something to look at". You must have a very high visual gradient to have systematization. In philosophy, before Descartes, there was no "system". Plato had no "system". Aristotle had no "system".
In the 19th century the French physicist Nicolas Léonard Sadi Carnot, who studied thermodynamics, pioneered the development of the concept of a "system" in the natural sciences. In 1824 he studied the system which he called the working substance (typically a body of water vapor) in steam engines, in regards to the system's ability to do work when heat is applied to it. The working substance could be put in contact with either a boiler, a cold reservoir (a stream of cold water), or a piston (to which the working body could do work by pushing on it). In 1850, the German physicist Rudolf Clausius generalized this picture to include the concept of the surroundings and began to use the term "working body" when referring to the system.
System (ISSN 0346-251X) is a peer-reviewed academic journal covering the applications of educational technology and applied linguistics to problems of foreign language teaching and learning. It was established in 1973 and is published quarterly by Elsevier.
In physics, a physical system is a portion of the physical universe chosen for analysis. Everything outside the system is known as the environment. The environment is ignored except for its effects on itself. In a physical system, a lower probability states that the vector is equivalent to a higher complexity.
The split between system and environment is the analyst's choice, generally made to simplify the analysis. For example, the water in a lake, the water in half of a lake, or an individual molecule of water in the lake can each be considered a physical system. An isolated system is one that has negligible interaction with its environment. Often a system in this sense is chosen to correspond to the more usual meaning of system, such as a particular machine.
In the study of quantum coherence the "system" may refer to the microscopic properties of an object (e.g. the mean of a pendulum bob), while the relevant "environment" may be the internal degrees of freedom, described classically by the pendulum's thermal vibrations.
In rugby union, the "99" call was a policy of simultaneous retaliation by the Lions during their 1974 tour to South Africa. The tour was marred by on-pitch violence, which the match officials did little to control and the relative absence of cameras compared to the modern game made citing and punishment after the fact unlikely.
Lions' captain Willie John McBride therefore instigated a policy of "one in, all in" - that is, when one Lion retaliated, all other Lions were expected to join in the melee or hit the nearest Springbok. By doing so, the referee would be unable to identify any single instigator and so would be left with the choice of sending off all or none of the team. In this respect, the "99" call was extremely successful, as no Lions player was sent off during the tour.
According to former Wales international and Lion John Taylor, the 99 call resulted from an incident that occurred during the Lions' 1968 South Africa tour that saw John O'Shea become the first and to date only Lion to have been sent off during a Lions tour. In 2013, Taylor recalled that during a Lions tour match against Eastern Transvaal,