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The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity can be conceptualized as quantifying the internal frictional force that arises between adjacent layers of fluid that are in relative motion. For instance, when a fluid is forced through a tube, it flows more near the tube's axis than near its walls. In such a case, experiments show; this is because a force is required to overcome the friction between the layers of the fluid which are in relative motion: the strength of this force is proportional to the viscosity. A fluid that has no resistance to shear stress is known as an inviscid fluid. Zero viscosity is observed only at low temperatures in superfluids. Otherwise, the second law of thermodynamics requires all fluids to have positive viscosity. A fluid with a high viscosity, such as pitch, may appear to be a solid; the word "viscosity" is derived from the Latin "viscum", meaning mistletoe and a viscous glue made from mistletoe berries.

In materials science and engineering, one is interested in understanding the forces, or stresses, involved in the deformation of a material. For instance, if the material were a simple spring, the answer would be given by Hooke's law, which says that the force experienced by a spring is proportional to the distance displaced from equilibrium. Stresses which can be attributed to the deformation of a material from some rest state are called elastic stresses. In other materials, stresses are present which can be attributed to the rate of change of the deformation over time; these are called. For instance, in a fluid such as water the stresses which arise from shearing the fluid do not depend on the distance the fluid has been sheared. Viscosity is the material property which relates the viscous stresses in a material to the rate of change of a deformation. Although it applies to general flows, it is easy to visualize and define in a simple shearing flow, such as a planar Couette flow. In the Couette flow, a fluid is trapped between two infinitely large plates, one fixed and one in parallel motion at constant speed u.

If the speed of the top plate is low enough in steady state the fluid particles move parallel to it, their speed varies from 0 at the bottom to u at the top. Each layer of fluid moves faster than the one just below it, friction between them gives rise to a force resisting their relative motion. In particular, the fluid applies on the top plate a force in the direction opposite to its motion, an equal but opposite force on the bottom plate. An external force is therefore required in order to keep the top plate moving at constant speed. In many fluids, the flow velocity is observed to vary linearly from zero at the bottom to u at the top. Moreover, the magnitude F of the force acting on the top plate is found to be proportional to the speed u and the area A of each plate, inversely proportional to their separation y: F = μ A u y; the proportionality factor μ is the viscosity of the fluid, with units of Pa ⋅ s. The ratio u / y is called the rate of shear deformation or shear velocity, is the derivative of the fluid speed in the direction perpendicular to the plates.

If the velocity does not vary linearly with y the appropriate generalization is τ = μ ∂ u ∂ y, where τ = F / A, ∂ u / ∂ y is the local shear velocity. This expression is referred to as Newton's law of viscosity. In shearing flows with planar symmetry, it is what defines μ, it is a special case of the general definition of viscosity, which can be expressed in coordinate-free form. Use of the Greek letter mu for the viscosity is common among mechanical and chemical engineers, as well as physicists. However, the Greek letter eta is used by chemists and the IUPAC; the viscosity μ is sometimes referred to as the shear viscosity. However, at least one author discourages the use of this terminology, noting that μ can appear in nonshearing flows in addition to shearing flows. In general terms, the viscous stresses in a fluid are defined as those resulting from the relative velocity of different fluid particles; as such, the viscous stresses. If the velocity gradients are small to a first approximation the vi

GLPI is an open source IT Asset Management, issue tracking system and service desk system. This software is distributed under the GNU General Public License; as an open source technology, anyone can modify or develop the code. This way, contributors can participate in the development of the software by committing free and open source supplementary modules on GitHub. GLPI is a web-based application helping companies to manage their information system; the solution is able to build an inventory of all the organization's assets and to manage administrative and financial tasks. The systems's functionalities help IT Administrators to create a database of technical resources, as well as a management and history of maintenances actions. Users can declare requests thanks to the Helpdesk feature; the GLPI Community based-project was directed by the INDEPNET association. Through the years, GLPI became used by both communities and companies, leading to a need of professional services around the system. Whereas the INDEPNET Association did not intend to offer services around the software, in 2008 the Association created a Partners' Network in order to achieve various objectives: The first objective was to build an ecosystem where Partners could participate in GLPI Project.

Secondly, Partners would financially support the association, in order to ensure the necessary software development. And the ecosystem would guarantee a service delivery through a known and identified Network, directly connected to INDEPNET. In 2009, Teclib’ started to integrate the software, developed the GLPI code and implemented new features. During summer 2015, the GLPI's Community leaders decided to transfer the roadmap management and the development leadership to Teclib’, so that Teclib´becomes editor of the GLPI system ensuring the software R&D; the code keeps its open source nature. The GLPI system continues to be improved thanks to the co-partnership between the community and the editor. GLPI Project is an open source and collaborative community of developers and IT experts gathered to develop the GLPI software; this collaboration is achieved by different means: installation and use of GLPI, GLPI tests, upgrades submissions, documentation participations, features request. Since 2003, GLPI has been developed through more than 80 versions.

Major releases include: As an ITSM software, the main features of GLPI are the following: Multi-entity management Multilingual management and support Multi user support and Multiple Authentication System Administrative and Financial management Inventory functionalities Incident and request management tracking and monitoring features Problem and change management Licenses management Assignment of equipment: location and groups Simplified interface to allow end users to fill a support ticket Asset and helpdesk reports: hardware, network or interventions Moreover, GLPI has many plugins that add further features. GLPI Software can be installed and set up in two different ways, either through the community forge or through a professional network. GLPI is using the following technologies: PHP 5.6 or higher MySQL / MariaDB regarding the database HTML for the Web pages JavaScript for some core functionalities CSS respecting style sheets XML for report generation IT asset management Issue tracking system Comparison of help desk issue tracking software Comparison of ticket-tracking systems Service desk OCS Inventory Antal, Barzan "Tony".

"7: Integrating OCS-NG with GLPI". OCS Inventory NG 1.02. Packt. ISBN 978-1-84951110-0. Patrice, Thebault. GLPI: Installation et configuration d'une solution de gestion de parc et de helpdesk. ENI. ISBN 978-2-7460-7008-0. Prodromou, Evelthon. "At Your Fingertips - Managing resource information in GLPI". Linux-magazine. No. 103. Official website

As a ship's boat, the pinnace is a light boat, propelled by oars or sails, carried aboard merchant and war vessels in the Age of Sail to serve as a tender. The pinnace was rowed but could be rigged with a sail for use in favorable winds. A pinnace would ferry passengers and mail, communicate between vessels, scout to sound anchorages, convey water and provisions, or carry armed sailors for boarding expeditions; the Spanish favored them as lightweight smuggling vessels. In modern parlance, "pinnace" has come to mean an auxiliary vessel that does not fit under the "launch" or "lifeboat" definitions. Identification of some pinnaces in contemporary historical documents is difficult because there was no standardization of pinnace design, be the type "small" or "large"; the term seems to have been applied to variants of what may be called the full-rigged pinnace, rather than the alternative use of the term for a larger vessel's boat. Furthermore, several ship type and rig terms were used in the 17th century, but with different definitions from those applied today.

Re-assessment of the design of some 17th-century ships not designated "pinnace" sometimes uncovers the unexpected. For example, in the 17th century, brigantine referred to a two-masted sailing ship, square-rigged on the foremast, fore-and-aft rigged on the main mast; the designation "brig" did not exist until the early 18th century, by which time vessels described as pinnaces had been well known for at least a century and a half. By the late 17th century, a brigantine in the Royal Navy was a small, square-rigged, two-masted ship that could be rowed as well as sailed. "Brig" referred to any ship, square-rigged on both masts. When "brig" and "brigantine" were too applied, other possibilities for ship types were obscured. There is the problem in sorting out what is meant by a "barque" in the early 17th century; the "barque" or "bark" rig as we understand it was not known in the first half of the 17th century, so what is meant by a "barque" is not clear. "When Governor Winthrop of the Massachusetts Bay Colony wrote of'barques', he referred to ships that were both'small' and'large' and weighed 12 to 40 tons", thereby suggesting the two types of pinnace and their usual range in tonnage.

Decked over, the "small" pinnace was able to support a variety of rigs, each of which conferred maximum utility to specific missions such as fishing, cargo transport and storage, or open ocean voyaging. The mature "small" pinnace design emerged as versatile with several different options and rigs possible; the expected popularity of the pinnace in the Massachusetts Bay Colony during the first half of the 17th century is documented. By the 1630s, historical records mention many ships trading or fishing with the Massachusetts Bay Colony, some of which were built in-colony. Above all, the fishing trade had taken hold off the shores of New England, was successful; the pinnace may have been the preferred, multi-use small ship of the first decades of English settlement in "Virginia". With the introduction of steam propulsion came the steam pinnace. Coal burning warships were vulnerable when at anchor, immobile until they could get a head of steam. Steam pinnaces were designed to be small enough to be carried by the capital ships they were allocated to and in addition to other duties were armed to act as picket boats.

One example of a ship utilizing many steam pinnace was HMS London in Zanzibar while suppressing the slave trade in the region:Slavery was legal in all Muslim countries, HM ships could only become involved with slaving when it took place on the high seas. The boats of HMS London were kept at five minutes' notice, ready equipped with water, salt pork, arms, local currency and a small cask of rum. Manned by eight or nine sailors, with a midshipman or junior lieutenant in command, a boat was away from the London for two or three weeks anchoring every night, the men off watch sleeping along the thwarts. History of the Museum's PinnaceRoyal Naval Museum