A clicker , sometimes called a cricket , is any device that makes a clicking sound, usually when deliberately activated by its user.
104-400: They usually consist of a piece of thin metal or plastic held in a casing so that the metal is slightly torqued; depressing one end of the metal causes it to pop out of alignment and releasing it causes it to pop back into alignment, each time making a sharp click. With some clickers, the user depresses the metal directly with thumb or finger; with others, a button extends above the surface of
208-476: A designer , a contractor , a construction manager , or other advisors); such specialists are normally appointed for their expertise in project delivery and construction management and will help the owner define the project brief , agree on a budget and schedule , liaise with relevant public authorities, and procure materials and the services of other specialists (the supply chain , comprising subcontractors and materials suppliers). Contracts are agreed for
312-578: A plasma (physics) is a metallic conductor and the charged particles in a plasma have many properties in common with those of electrons in elemental metals, particularly for white dwarf stars. Metals are relatively good conductors of heat , which in metals is transported mainly by the conduction electrons. At higher temperatures the electrons can occupy slightly higher energy levels given by Fermi–Dirac statistics . These have slightly higher momenta ( kinetic energy ) and can pass on thermal energy. The empirical Wiedemann–Franz law states that in many metals
416-435: A semiconducting metalloid such as boron has an electrical conductivity 1.5 × 10 S/cm. With one exception, metallic elements reduce their electrical conductivity when heated. Plutonium increases its electrical conductivity when heated in the temperature range of around −175 to +125 °C, with anomalously large thermal expansion coefficient and a phase change from monoclinic to face-centered cubic near 100 °C. There
520-422: A "live" environment (where residents or businesses remain living in or operating on the site) requires particular care, planning and communication. When applicable, a proposed construction project must comply with local land-use planning policies including zoning and building code requirements. A project will normally be assessed (by the 'authority having jurisdiction', AHJ, typically the municipality where
624-454: A base metal as it is oxidized relatively easily, although it does not react with HCl. The term noble metal (also for elements) is commonly used in opposition to base metal . Noble metals are less reactive, resistant to corrosion or oxidation , unlike most base metals . They tend to be precious metals, often due to perceived rarity. Examples include gold, platinum, silver, rhodium , iridium, and palladium. In alchemy and numismatics ,
728-445: A building or other asset that affect safety, including its use, expansion, structural integrity, and fire protection , usually require municipality approval. Depending on the type of project, mortgage bankers , accountants , and cost engineers may participate in creating an overall plan for the financial management of a construction project. The presence of the mortgage banker is highly likely, even in relatively small projects since
832-640: A business to lead both design and construction ( design-build ); or they may directly appoint a designer, contractor and specialist subcontractors ( construction management ). Some forms of procurement emphasize collaborative relationships ( partnering , alliancing) between the client, the contractor, and other stakeholders within a construction project, seeking to ameliorate often highly competitive and adversarial industry practices. DfMA (design for manufacture and assembly) approaches also emphasize early collaboration with manufacturers and suppliers regarding products and components. Construction or refurbishment work in
936-479: A conceptual cost estimate performed by a building estimator . As portions of a project are completed, they may be sold, supplanting one lender or owner for another, while the logistical requirements of having the right trades and materials available for each stage of the building construction project carry forward. Public–private partnerships (PPPs) or private finance initiatives (PFIs) may also be used to help deliver major projects. According to McKinsey in 2019,
1040-443: A few—beryllium, chromium, manganese, gallium, and bismuth—are brittle. Arsenic and antimony, if admitted as metals, are brittle. Low values of the ratio of bulk elastic modulus to shear modulus ( Pugh's criterion ) are indicative of intrinsic brittleness. A material is brittle if it is hard for dislocations to move, which is often associated with large Burgers vectors and only a limited number of slip planes. A refractory metal
1144-511: A lower atomic number) by neutron capture , with the two main modes of this repetitive capture being the s-process and the r-process . In the s-process ("s" stands for "slow"), singular captures are separated by years or decades, allowing the less stable nuclei to beta decay , while in the r-process ("rapid"), captures happen faster than nuclei can decay. Therefore, the s-process takes a more-or-less clear path: for example, stable cadmium-110 nuclei are successively bombarded by free neutrons inside
SECTION 10
#17331053098701248-514: A real metal. In this respect they resemble degenerate semiconductors . This explains why the electrical properties of semimetals are partway between those of metals and semiconductors . There are additional types, in particular Weyl and Dirac semimetals . The classic elemental semimetallic elements are arsenic , antimony , bismuth , α- tin (gray tin) and graphite . There are also chemical compounds , such as mercury telluride (HgTe), and some conductive polymers . Metallic elements up to
1352-407: A result of a neutron star merger, thereby increasing the abundance of elements heavier than helium in the interstellar medium . When gravitational attraction causes this matter to coalesce and collapse new stars and planets are formed . The Earth's crust is made of approximately 25% of metallic elements by weight, of which 80% are light metals such as sodium, magnesium, and aluminium. Despite
1456-483: A role as investments and a store of value . Palladium and platinum, as of summer 2024, were valued at slightly less than half the price of gold, while silver is substantially less expensive. In electrochemistry, a valve metal is a metal which passes current in only one direction due to the formation of any insulating oxide later. There are many ceramic compounds which have metallic electrical conduction, but are not simple combinations of metallic elements. (They are not
1560-433: A rule is inapplicable (the bridge design will not cause a collapse), or that the custom is no longer needed (acceptance of live-work spaces has grown in the community). During the construction of a building, a municipal building inspector usually inspects the ongoing work periodically to ensure that construction adheres to the approved plans and the local building code. Once construction is complete, any later changes made to
1664-400: A star until they form cadmium-115 nuclei which are unstable and decay to form indium-115 (which is nearly stable, with a half-life 30 000 times the age of the universe). These nuclei capture neutrons and form indium-116, which is unstable, and decays to form tin-116, and so on. In contrast, there is no such path in the r-process. The s-process stops at bismuth due to the short half-lives of
1768-516: A treat, a click allows the owner to mark the precise moment the desired behavior is executed. This sound technology article is a stub . You can help Misplaced Pages by expanding it . Metal A metal (from Ancient Greek μέταλλον ( métallon ) 'mine, quarry, metal') is a material that, when polished or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. These properties are all associated with having electrons available at
1872-410: Is a verb : the act of building, and the noun is construction: how something is built or the nature of its structure. In its most widely used context, construction covers the processes involved in delivering buildings , infrastructure , industrial facilities, and associated activities through to the end of their life. It typically starts with planning , financing , and design that continues until
1976-403: Is a metal that is very resistant to heat and wear. Which metals belong to this category varies; the most common definition includes niobium, molybdenum, tantalum, tungsten, and rhenium as well as their alloys. They all have melting points above 2000 °C, and a high hardness at room temperature. Several compounds such as titanium nitride are also described as refractory metals. A white metal
2080-611: Is any of a range of white-colored alloys with relatively low melting points used mainly for decorative purposes. In Britain, the fine art trade uses the term "white metal" in auction catalogues to describe foreign silver items which do not carry British Assay Office marks, but which are nonetheless understood to be silver and are priced accordingly. A heavy metal is any relatively dense metal, either single element or multielement. Magnesium , aluminium and titanium alloys are light metals of significant commercial importance. Their densities of 1.7, 2.7 and 4.5 g/cm range from 19 to 56% of
2184-480: Is composed mostly of iron, is thought to be the source of Earth's protective magnetic field. The core lies above Earth's solid inner core and below its mantle. If it could be rearranged into a column having a 5 m (54 sq ft) footprint it would have a height of nearly 700 light years. The magnetic field shields the Earth from the charged particles of the solar wind, and cosmic rays that would otherwise strip away
SECTION 20
#17331053098702288-611: Is due to the freely moving electrons which reflect light. Although most elemental metals have higher densities than nonmetals , there is a wide variation in their densities, lithium being the least dense (0.534 g/cm ) and osmium (22.59 g/cm ) the most dense. Some of the 6d transition metals are expected to be denser than osmium, but their known isotopes are too unstable for bulk production to be possible Magnesium, aluminium and titanium are light metals of significant commercial importance. Their respective densities of 1.7, 2.7, and 4.5 g/cm can be compared to those of
2392-620: Is evidence that this and comparable behavior in transuranic elements is due to more complex relativistic and spin interactions which are not captured in simple models. All of the metallic alloys as well as conducting ceramics and polymers are metals by the same definition; for instance titanium nitride has delocalized states at the Fermi level. They have electrical conductivities similar to those of elemental metals. Liquid forms are also metallic conductors or electricity, for instance mercury . In normal conditions no gases are metallic conductors. However,
2496-544: Is no external voltage . When a voltage is applied some move a little faster in a given direction, some a little slower so there is a net drift velocity which leads to an electric current. This involves small changes in which wavefunctions the electrons are in, changing to those with the higher momenta. Quantum mechanics dictates that one can only have one electron in a given state, the Pauli exclusion principle . Therefore there have to be empty delocalized electron states (with
2600-474: Is not. In the context of metals, an alloy is a substance having metallic properties which is composed of two or more elements . Often at least one of these is a metallic element; the term "alloy" is sometimes used more generally as in silicon–germanium alloys. An alloy may have a variable or fixed composition. For example, gold and silver form an alloy in which the proportions of gold or silver can be varied; titanium and silicon form an alloy TiSi 2 in which
2704-575: Is positioned at the center of a cube of eight others. In fcc and hcp, each atom is surrounded by twelve others, but the stacking of the layers differs. Some metals adopt different structures depending on the temperature. Many other metals with different elements have more complicated structures, such as rock-salt structure in titanium nitride or perovskite (structure) in some nickelates. The electronic structure of metals means they are relatively good conductors of electricity . The electrons all have different momenta , which average to zero when there
2808-405: Is the discipline of safely and efficiently tearing down buildings and other artificial structures . Demolition contrasts with deconstruction , which involves taking a building apart while carefully preserving valuable elements for reuse purposes ( recycling – see also circular economy ). The output of the global construction industry was worth an estimated $ 10.8 trillion in 2017, and in 2018
2912-937: Is the process of adding structures to areas of land, also known as real property sites. Typically, a project is instigated by or with the owner of the property (who may be an individual or an organisation); occasionally, land may be compulsorily purchased from the owner for public use. Residential construction may be undertaken by individual land-owners ( self-built ), by specialist housebuilders , by property developers , by general contractors , or by providers of public or social housing (e.g.: local authorities, housing associations ). Where local zoning or planning policies allow, mixed-use developments may comprise both residential and non-residential construction (e.g.: retail, leisure, offices, public buildings, etc.). Residential construction practices, technologies , and resources must conform to local building authority's regulations and codes of practice . Materials readily available in
3016-425: Is the proportion of its matter made up of the heavier chemical elements. The strength and resilience of some metals has led to their frequent use in, for example, high-rise building and bridge construction , as well as most vehicles, many home appliances , tools, pipes, and railroad tracks. Precious metals were historically used as coinage , but in the modern era, coinage metals have extended to at least 23 of
3120-413: Is the second largest construction market with a 2018 output of $ 1.581 trillion. Construction is a major source of employment in most countries; high reliance on small businesses, and under-representation of women are common traits. For example: According to McKinsey research, productivity growth per worker in construction has lagged behind many other industries across different countries including in
3224-550: The Bronze Age , a class of professional craftsmen , like bricklayers and carpenters , appeared. Occasionally, slaves were used for construction work. In the Middle Ages , the artisan craftsmen were organized into guilds . In the 19th century, steam-powered machinery appeared, and later, diesel- and electric-powered vehicles such as cranes , excavators and bulldozers . Fast-track construction has been increasingly popular in
Clicker - Misplaced Pages Continue
3328-469: The Burgers vector of the dislocations are fairly small, which also means that the energy needed to produce one is small. In contrast, in an ionic compound like table salt the Burgers vectors are much larger and the energy to move a dislocation is far higher. Reversible elastic deformation in metals can be described well by Hooke's Law for the restoring forces, where the stress is linearly proportional to
3432-484: The Fermi level , as against nonmetallic materials which do not. Metals are typically ductile (can be drawn into wires) and malleable (they can be hammered into thin sheets). A metal may be a chemical element such as iron ; an alloy such as stainless steel ; or a molecular compound such as polymeric sulfur nitride . The general science of metals is called metallurgy , a subtopic of materials science ; aspects of
3536-587: The United States and in European countries. In the United States, construction productivity per worker has declined by half since the 1960s. The twenty-five largest countries in the world by construction GVA (2018) Some workers may be engaged in manual labour as unskilled or semi-skilled workers; they may be skilled tradespeople; or they may be supervisory or managerial personnel. Under safety legislation in
3640-474: The architect , engineer or builder acts for the client as the project coordinator. They design the works, prepare specifications and design deliverables (models, drawings, etc.), administer the contract, tender the works, and manage the works from inception to completion. In parallel, there are direct contractual links between the client and the main contractor, who, in turn, has direct contractual relationships with subcontractors. The arrangement continues until
3744-415: The periodic table . If there are several, the most stable allotrope is considered. The situation changes with pressure: at extremely high pressures, all elements (and indeed all substances) are expected to metallize. Arsenic (As) has both a stable metallic allotrope and a metastable semiconducting allotrope at standard conditions. A similar situation affects carbon (C): graphite is metallic, but diamond
3848-539: The strain . A temperature change may lead to the movement of structural defects in the metal such as grain boundaries , point vacancies , line and screw dislocations , stacking faults and twins in both crystalline and non-crystalline metals. Internal slip , creep , and metal fatigue may also ensue. The atoms of simple metallic substances are often in one of three common crystal structures , namely body-centered cubic (bcc), face-centered cubic (fcc), and hexagonal close-packed (hcp). In bcc, each atom
3952-414: The type of building , non-residential building construction can be procured by a wide range of private and public organisations, including local authorities, educational and religious bodies, transport undertakings, retailers, hoteliers, property developers, financial institutions and other private companies. Most construction in these sectors is undertaken by general contractors . Civil engineering covers
4056-486: The vicinity of iron (in the periodic table) are largely made via stellar nucleosynthesis . In this process, lighter elements from hydrogen to silicon undergo successive fusion reactions inside stars, releasing light and heat and forming heavier elements with higher atomic numbers. Heavier elements are not usually formed this way since fusion reactions involving such nuclei would consume rather than release energy. Rather, they are largely synthesised (from elements with
4160-581: The "vast majority of large construction projects go over budget and take 20% longer than expected". A construction project is a complex net of construction contracts and other legal obligations, each of which all parties must carefully consider. A contract is the exchange of a set of obligations between two or more parties, and provides structures to manage issues. For example, construction delays can be costly, so construction contracts set out clear expectations and clear paths to manage delays. Poorly drafted contracts can lead to confusion and costly disputes. At
4264-461: The 21st century. Some estimates suggest that 40% of construction projects are now fast-track construction. Broadly, there are three sectors of construction: buildings, infrastructure and industrial: The industry can also be classified into sectors or markets. For example, Engineering News-Record ( ENR ), a US-based construction trade magazine, has compiled and reported data about the size of design and construction contractors. In 2014, it split
Clicker - Misplaced Pages Continue
4368-447: The 21st-century introduction of building information modeling (BIM) processes has involved the use of computer-generated models that can be used in their own right or to generate drawings and other visualisations as well as capturing non-geometric data about building components and systems. On some projects, work on-site will not start until design work is largely complete; on others, some design work may be undertaken concurrently with
4472-439: The Fermi energy. Many elements and compounds become metallic under high pressures, for example, iodine gradually becomes a metal at a pressure of between 40 and 170 thousand times atmospheric pressure . Sodium becomes a nonmetal at pressure of just under two million times atmospheric pressure, and at even higher pressures it is expected to become a metal again. When discussing the periodic table and some chemical properties
4576-585: The United Kingdom, for example, construction workers are defined as people "who work for or under the control of a contractor on a construction site"; in Canada, this can include people whose work includes ensuring conformance with building codes and regulations, and those who supervise other workers. Laborers comprise a large grouping in most national construction industries. In the United States, for example, in May 2021
4680-425: The addition of chromium , nickel , and molybdenum to carbon steels (more than 10%) results in stainless steels with enhanced corrosion resistance. Other significant metallic alloys are those of aluminum , titanium , copper , and magnesium . Copper alloys have been known since prehistory— bronze gave the Bronze Age its name—and have many applications today, most importantly in electrical wiring. The alloys of
4784-599: The air to form oxides over various timescales ( potassium burns in seconds while iron rusts over years) which depend upon whether the native oxide forms a passivation layer that acts as a diffusion barrier . Some others, like palladium , platinum , and gold , do not react with the atmosphere at all; gold can form compounds where it gains an electron (aurides, e.g. caesium auride ). The oxides of elemental metals are often basic . However, oxides with very high oxidation states such as CrO 3 , Mn 2 O 7 , and OsO 4 often have strictly acidic reactions; and oxides of
4888-413: The area generally dictate the construction materials used (e.g.: brick versus stone versus timber ). Costs of construction on a per square meter (or per square foot) basis for houses can vary dramatically based on site conditions, access routes, local regulations, economies of scale (custom-designed homes are often more expensive to build) and the availability of skilled tradespeople. Depending upon
4992-554: The asset as an advanced technological system requiring close integration of many sub-systems and their individual components, including sustainability. For buildings, building engineering is an emerging discipline that attempts to meet this new challenge. Traditionally, design has involved the production of sketches , architectural and engineering drawings , and specifications . Until the late 20th century, drawings were largely hand- drafted ; adoption of computer-aided design (CAD) technologies then improved design productivity, while
5096-415: The asset is built and ready for use. Construction also covers repairs and maintenance work, any works to expand, extend and improve the asset, and its eventual demolition , dismantling or decommissioning . The construction industry contributes significantly to many countries' gross domestic products ( GDP ). Global expenditure on construction activities was about $ 4 trillion in 2012. In 2022, expenditure on
5200-419: The budget on the job, and a construction manager , design engineer , construction engineer or architect supervises it. Those involved with the design and execution must consider zoning requirements and legal issues, environmental impact of the project, scheduling , budgeting and bidding , construction site safety , availability and transportation of building materials , logistics, and inconvenience to
5304-478: The casing so that depressing the button makes the metal click. Clickers were first used by marine mammal trainer Karen Pryor as a way of communicating with their animals. Dolphins and whales communicate underwater through a series of clicks and whistles known as echolocation , and the clicker allowed a trainer to produce signals they were more likely to understand. Nowadays, clickers are used to train all kinds of animals, most commonly dogs. When associated with
SECTION 50
#17331053098705408-445: The chemical elements. There is also extensive use of multi-element metals such as titanium nitride or degenerate semiconductors in the semiconductor industry. The history of refined metals is thought to begin with the use of copper about 11,000 years ago. Gold, silver, iron (as meteoric iron), lead, and brass were likewise in use before the first known appearance of bronze in the fifth millennium BCE. Subsequent developments include
5512-447: The client enters into separate contracts with the designer (architect or engineer), a construction manager , and individual trade contractors . The client takes on the contractual role, while the construction or project manager provides the active role of managing the separate trade contracts, and ensuring that they complete all work smoothly and effectively together. This approach is often used to speed up procurement processes, to allow
5616-410: The client greater flexibility in design variation throughout the contract, to enable the appointment of individual work contractors, to separate contractual responsibility on each individual throughout the contract, and to provide greater client control. In the industrialized world, construction usually involves the translation of designs into reality. Most commonly (i.e.: in a design-bid-build project),
5720-533: The construction industry exceeded $ 11 trillion a year, equivalent to about 13 percent of global GDP . This spending was forecasted to rise to around $ 14.8 trillion in 2030. The construction industry promotes economic development and brings many non-monetary benefits to many countries, but it is one of the most hazardous industries. For example, about 20% (1,061) of US industry fatalities in 2019 happened in construction. The first huts and shelters were constructed by hand or with simple tools. As cities grew during
5824-665: The construction sector employed just over 7.5 million people, of whom just over 820,000 were laborers, while 573,000 were carpenters , 508,000 were electricians , 258,000 were equipment operators and 230,000 were construction managers. Like most business sectors, there is also substantial white-collar employment in construction – 681,000 US workers were recorded by the United States Department of Labor as in 'office and administrative support occupations' in May 2021. Large-scale construction requires collaboration across multiple disciplines. A project manager normally manages
5928-750: The data into nine market segments: transportation, petroleum , buildings, power, industrial, water, manufacturing, sewage/waste, telecom , hazardous waste , and a tenth category for other projects. ENR used data on transportation, sewage, hazardous waste and water to rank firms as heavy contractors. The Standard Industrial Classification and the newer North American Industry Classification System classify companies that perform or engage in construction into three subsectors: building construction, heavy and civil engineering construction, and specialty trade contractors. There are also categories for professional services firms (e.g., engineering , architecture , surveying , project management ). Building construction
6032-426: The delivery of services by all businesses, alongside other detailed plans aimed at ensuring legal, timely, on-budget and safe delivery of the specified works. Design, finance, and legal aspects overlap and interrelate. The design must be not only structurally sound and appropriate for the use and location, but must also be financially possible to build, and legal to use. The financial structure must be adequate to build
6136-406: The densities of other structural metals, such as iron (7.9) and copper (8.9) and their alloys. The term base metal refers to a metal that is easily oxidized or corroded , such as reacting easily with dilute hydrochloric acid (HCl) to form a metal chloride and hydrogen . The term is normally used for the elements, and examples include iron, nickel , lead , and zinc. Copper is considered
6240-440: The design provided and must pay amounts that are legally owed. Legal structures integrate design with other activities and enforce financial and other construction processes. These processes also affect procurement strategies. Clients may, for example, appoint a business to design the project, after which a competitive process is undertaken to appoint a lead contractor to construct the asset ( design–bid–build ); they may appoint
6344-451: The design team is employed by (i.e. in contract with) the property owner. Depending upon the type of project, a design team may include architects , civil engineers , mechanical engineers , electrical engineers , structural engineers , fire protection engineers , planning consultants , architectural consultants, and archaeological consultants. A 'lead designer' will normally be identified to help coordinate different disciplinary inputs to
SECTION 60
#17331053098706448-821: The design, construction, and maintenance of the physical and naturally built environment , including public works such as roads, bridges, canals, dams, tunnels, airports, water and sewerage systems, pipelines, and railways. Some general contractors have expertise in civil engineering; civil engineering contractors are firms dedicated to work in this sector, and may specialise in particular types of infrastructure. Industrial construction includes offshore construction (mainly of energy installations: oil and gas platforms , wind power ), mining and quarrying , refineries , breweries , distilleries and other processing plants, power stations , steel mills , warehouses and factories . Some construction projects are small renovations or repair jobs, like repainting or fixing leaks, where
6552-443: The desire to prevent indisputably bad phenomena, e.g. explosions or bridge collapses. Other legal requirements come from malum prohibitum considerations, or factors that are a matter of custom or expectation, such as isolating businesses from a business district or residences from a residential district. An attorney may seek changes or exemptions in the law that governs the land where the building will be built, either by arguing that
6656-495: The detailed structure of the metal's ion lattice. Taking into account the positive potential caused by the arrangement of the ion cores enables consideration of the electronic band structure and binding energy of a metal. Various models are applicable, the simplest being the nearly free electron model . Modern methods such as density functional theory are typically used. The elements which form metals usually form cations through electron loss. Most will react with oxygen in
6760-535: The early stages of on-site activity (for example, work on a building's foundations may commence while designers are still working on the detailed designs of the building's internal spaces). Some projects may include elements that are designed for off-site construction (see also prefabrication and modular building ) and are then delivered to the site ready for erection, installation or assembly. Once contractors and other relevant professionals have been appointed and designs are sufficiently advanced, work may commence on
6864-429: The electronic and thermal properties are also within the scope of condensed matter physics and solid-state chemistry , it is a multidisciplinary topic. In colloquial use materials such as steel alloys are referred to as metals, while others such as polymers, wood or ceramics are nonmetallic materials . A metal conducts electricity at a temperature of absolute zero , which is a consequence of delocalized states at
6968-456: The elements from fermium (Fm) onwards are shown in gray because they are extremely radioactive and have never been produced in bulk. Theoretical and experimental evidence suggests that these uninvestigated elements should be metals, except for oganesson (Og) which DFT calculations indicate would be a semiconductor. Metallic Network covalent Molecular covalent Single atoms Unknown Background color shows bonding of simple substances in
7072-433: The f-block elements. They have a strong affinity for oxygen and mostly exist as relatively low-density silicate minerals. Chalcophile elements are mainly the less reactive d-block elements, and the period 4–6 p-block metals. They are usually found in (insoluble) sulfide minerals. Being denser than the lithophiles, hence sinking lower into the crust at the time of its solidification, the chalcophiles tend to be less abundant than
7176-412: The first feature of the permanent structure has been put in place, such as pile driving, or the pouring of slabs or footings. Commissioning is the process of verifying that all subsystems of a new building (or other assets) work as intended to achieve the owner's project requirements and as designed by the project's architects and engineers. A period after handover (or practical completion) during which
7280-720: The higher momenta) available at the highest occupied energies as sketched in the Figure. In a semiconductor like silicon or a nonmetal like strontium titanate there is an energy gap between the highest filled states of the electrons and the lowest unfilled, so no accessible states with slightly higher momenta. Consequently, semiconductors and nonmetals are poor conductors, although they can carry some current when doped with elements that introduce additional partially occupied energy states at higher temperatures. The elemental metals have electrical conductivity values of from 6.9 × 10 S /cm for manganese to 6.3 × 10 S/cm for silver . In contrast,
7384-436: The known examples of half-metals are oxides , sulfides , or Heusler alloys . A semimetal is a material with a small energy overlap between the bottom of the conduction band and the top of the valence band , but they do not overlap in momentum space . Unlike a regular metal, semimetals have charge carriers of both types (holes and electrons), although the charge carriers typically occur in much smaller numbers than in
7488-482: The less electropositive metals such as BeO, Al 2 O 3 , and PbO, can display both basic and acidic properties. The latter are termed amphoteric oxides. The elements that form exclusively metallic structures under ordinary conditions are shown in yellow on the periodic table below. The remaining elements either form covalent network structures (light blue), molecular covalent structures (dark blue), or remain as single atoms (violet). Astatine (At), francium (Fr), and
7592-408: The lithophiles. On the other hand, gold is a siderophile, or iron-loving element. It does not readily form compounds with either oxygen or sulfur. At the time of the Earth's formation, and as the most noble (inert) of metallic elements, gold sank into the core due to its tendency to form high-density metallic alloys. Consequently, it is relatively rare. Some other (less) noble ones—molybdenum, rhenium,
7696-407: The metallic alloys in use today, the alloys of iron ( steel , stainless steel , cast iron , tool steel , alloy steel ) make up the largest proportion both by quantity and commercial value. Iron alloyed with various proportions of carbon gives low-, mid-, and high-carbon steels, with increasing carbon levels reducing ductility and toughness. The addition of silicon will produce cast irons, while
7800-401: The next two elements, polonium and astatine, which decay to bismuth or lead. The r-process is so fast it can skip this zone of instability and go on to create heavier elements such as thorium and uranium. Metals condense in planets as a result of stellar evolution and destruction processes. Stars lose much of their mass when it is ejected late in their lifetimes, and sometimes thereafter as
7904-493: The nitrogen. However, unlike most elemental metals, ceramic metals are often not particularly ductile. Their uses are widespread, for instance titanium nitride finds use in orthopedic devices and as a wear resistant coating. In many cases their utility depends upon there being effective deposition methods so they can be used as thin film coatings. There are many polymers which have metallic electrical conduction, typically associated with extended aromatic components such as in
8008-618: The older structural metals, like iron at 7.9 and copper at 8.9 g/cm . The most common lightweight metals are aluminium and magnesium alloys. Metals are typically malleable and ductile, deforming under stress without cleaving . The nondirectional nature of metallic bonding contributes to the ductility of most metallic solids, where the Peierls stress is relatively low allowing for dislocation motion, and there are also many combinations of planes and directions for plastic deformation . Due to their having close packed arrangements of atoms
8112-702: The other three metals have been developed relatively recently; due to their chemical reactivity they need electrolytic extraction processes. The alloys of aluminum, titanium, and magnesium are valued for their high strength-to-weight ratios; magnesium can also provide electromagnetic shielding . These materials are ideal for situations where high strength-to-weight ratio is more important than material cost, such as in aerospace and some automotive applications. Alloys specially designed for highly demanding applications, such as jet engines , may contain more than ten elements. Metals can be categorised by their composition, physical or chemical properties. Categories described in
8216-486: The overall budget is adequate, presenting a temporary issue. Cost overruns with government projects have occurred when the contractor identified change orders or project changes that increased costs, which are not subject to competition from other firms as they have already been eliminated from consideration after the initial bid. Fraud is also an issue of growing significance within construction. Large projects can involve highly complex financial plans and often start with
8320-441: The overall design. This may be aided by integration of previously separate disciplines (often undertaken by separate firms) into multi-disciplinary firms with experts from all related fields, or by firms establishing relationships to support design-build processes. The increasing complexity of construction projects creates the need for design professionals trained in all phases of a project's life-cycle and develop an appreciation of
8424-400: The overall scarcity of some heavier metals such as copper, they can become concentrated in economically extractable quantities as a result of mountain building, erosion, or other geological processes. Metallic elements are primarily found as lithophiles (rock-loving) or chalcophiles (ore-loving). Lithophile elements are mainly the s-block elements, the more reactive of the d-block elements, and
8528-409: The owner may act as designer, paymaster and laborer for the entire project. However, more complex or ambitious projects usually require additional multi-disciplinary expertise and manpower, so the owner may commission one or more specialist businesses to undertake detailed planning, design, construction and handover of the work. Often the owner will appoint one business to oversee the project (this may be
8632-405: The owner may identify any shortcomings in relation to the building specification ('defects'), with a view to the contractor correcting the defect. Maintenance involves functional checks, servicing, repairing or replacing of necessary devices, equipment, machinery , building infrastructure, and supporting utilities in industrial, business, governmental, and residential installations. Demolition
8736-478: The owner's equity in the property is the most obvious source of funding for a building project. Accountants act to study the expected monetary flow over the life of the project and to monitor the payouts throughout the process. Professionals including cost engineers, estimators and quantity surveyors apply expertise to relate the work and materials involved to a proper valuation. Financial planning ensures adequate safeguards and contingency plans are in place before
8840-420: The platinum group metals (ruthenium, rhodium, palladium, osmium, iridium, and platinum), germanium, and tin—can be counted as siderophiles but only in terms of their primary occurrence in the Earth (core, mantle, and crust), rather the crust. These otherwise occur in the crust, in small quantities, chiefly as chalcophiles (less so in their native form). The rotating fluid outer core of the Earth's interior, which
8944-547: The polymers indicated in the Figure. The conduction of the aromatic regions is similar to that of graphite, so is highly directional. A half-metal is any substance that acts as a conductor to electrons of one spin orientation, but as an insulator or semiconductor to those of the opposite spin. They were first described in 1983, as an explanation for the electrical properties of manganese -based Heusler alloys . Although all half-metals are ferromagnetic (or ferrimagnetic ), most ferromagnets are not half-metals. Many of
9048-401: The production of early forms of steel; the discovery of sodium —the first light metal —in 1809; the rise of modern alloy steels ; and, since the end of World War II, the development of more sophisticated alloys. Most metals are shiny and lustrous , at least when polished, or fractured. Sheets of metal thicker than a few micrometres appear opaque, but gold leaf transmits green light. This
9152-414: The project brief and then selects a preferred supplier. Often this will be a consortium involving a design firm and a contractor (sometimes more than one of each). In the United States, departments of transportation usually use design-build contracts as a way of progressing projects where states lack the skills or resources, particularly for very large projects. In a construction management arrangement,
9256-435: The project is ready for handover. Design-build became more common from the late 20th century, and involves the client contracting a single entity to provide design and construction. In some cases, the design-build package can also include finding the site, arranging funding and applying for all necessary statutory consents. Typically, the client invites several Design & Build (D&B) contractors to submit proposals to meet
9360-405: The project is started, and ensures that the plan is properly executed over the life of the project. Construction projects can suffer from preventable financial problems. Underbids happen when builders ask for too little money to complete the project. Cash flow problems exist when the present amount of funding cannot cover the current costs for labour and materials; such problems may arise even when
9464-518: The project site. Typically, a construction site will include a secure perimeter to restrict unauthorised access, site access control points, office and welfare accommodation for personnel from the main contractor and other firms involved in the project team, and storage areas for materials, machinery and equipment. According to the McGraw-Hill Dictionary of Architecture and Construction's definition, construction may be said to have started when
9568-745: The project will be located) for its potential impacts on neighbouring properties, and upon existing infrastructure (transportation, social infrastructure, and utilities including water supply, sewerage, electricity, telecommunications, etc.). Data may be gathered through site analysis , site surveys and geotechnical investigations . Construction normally cannot start until planning permission has been granted, and may require preparatory work to ensure relevant infrastructure has been upgraded before building work can commence. Preparatory works will also include surveys of existing utility lines to avoid damage-causing outages and other hazardous situations. Some legal requirements come from malum in se considerations, or
9672-628: The public, including those caused by construction delays . Some models and policy-making organisations promote the engagement of local labour in construction projects as a means of tackling social exclusion and addressing skill shortages. In the UK, the Joseph Rowntree Foundation reported in 2000 on 25 projects which had aimed to offer training and employment opportunities for locally based school leavers and unemployed people. The Foundation published "a good practice resource book" in this regard at
9776-408: The ratio between thermal and electrical conductivities is proportional to temperature, with a proportionality constant that is roughly the same for all metals. The contribution of a metal's electrons to its heat capacity and thermal conductivity, and the electrical conductivity of the metal itself can be approximately calculated from the free electron model . However, this does not take into account
9880-415: The ratio of the two components is fixed (also known as an intermetallic compound ). Most pure metals are either too soft, brittle, or chemically reactive for practical use. Combining different ratios of metals and other elements in alloys modifies the properties to produce desirable characteristics, for instance more ductile, harder, resistant to corrosion, or have a more desirable color and luster. Of all
9984-489: The sale price of the metal(s) involved make it economically feasible to mine lower concentration sources. Construction This is an accepted version of this page Construction is a general term meaning the art and science of forming objects , systems , or organizations . It comes from the Latin word constructio (from com- "together" and struere "to pile up") and Old French construction . To 'construct'
10088-416: The same as cermets which are composites of a non-conducting ceramic and a conducting metal.) One set, the transition metal nitrides has significant ionic character to the bonding, so can be classified as both ceramics and metals. They have partially filled states at the Fermi level so are good thermal and electrical conductors, and there is often significant charge transfer from the transition metal atoms to
10192-647: The same time. Use of local labour and local materials were specified for the construction of the Danish Storebaelt bridge , but there were legal issues which were challenged in court and addressed by the European Court of Justice in 1993. The court held that a contract condition requiring use of local labour and local materials was incompatible with EU treaty principles . Later UK guidance noted that social and employment clauses, where used, must be compatible with relevant EU regulation. Employment of local labour
10296-473: The start of a project, legal advisors seek to identify ambiguities and other potential sources of trouble in the contract structures, and to present options for preventing problems. During projects, they work to avoid and resolve conflicts that arise. In each case, the lawyer facilitates an exchange of obligations that matches the reality of the project. Design-bid-build is the most common and well-established method of construction procurement. In this arrangement,
10400-584: The subsections below include ferrous and non-ferrous metals; brittle metals and refractory metals ; white metals; heavy and light metals; base , noble , and precious metals as well as both metallic ceramics and polymers . The term "ferrous" is derived from the Latin word meaning "containing iron". This can include pure iron, such as wrought iron , or an alloy such as steel . Ferrous metals are often magnetic , but not exclusively. Non-ferrous metals and alloys lack appreciable amounts of iron. While nearly all elemental metals are malleable or ductile,
10504-474: The term base metal is contrasted with precious metal , that is, those of high economic value. Most coins today are made of base metals with low intrinsic value ; in the past, coins frequently derived their value primarily from their precious metal content; gold , silver , platinum , and palladium each have an ISO 4217 currency code. Currently they have industrial uses such as platinum and palladium in catalytic converters , are used in jewellery and also
10608-634: The term metal is often used to denote those elements which in pure form and at standard conditions are metals in the sense of electrical conduction mentioned above. The related term metallic may also be used for types of dopant atoms or alloying elements. In astronomy metal refers to all chemical elements in a star that are heavier than helium . In this sense the first four "metals" collecting in stellar cores through nucleosynthesis are carbon , nitrogen , oxygen , and neon . A star fuses lighter atoms, mostly hydrogen and helium, into heavier atoms over its lifetime. The metallicity of an astronomical object
10712-496: The upper atmosphere (including the ozone layer that limits the transmission of ultraviolet radiation). Metallic elements are often extracted from the Earth by mining ores that are rich sources of the requisite elements, such as bauxite . Ores are located by prospecting techniques, followed by the exploration and examination of deposits. Mineral sources are generally divided into surface mines , which are mined by excavation using heavy equipment, and subsurface mines . In some cases,
10816-455: Was forecast to rise to $ 12.9 trillion by 2022, and to around $ 14.8 trillion in 2030. As a sector, construction accounts for more than 10% of global GDP (in developed countries , construction comprises 6–9% of GDP), and employs around 7% of the total employed workforce around the globe (accounting for over 273 million full- and part-time jobs in 2014). Since 2010, China has been the world's largest single construction market. The United States
#869130