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110-409: Breathing apparatus may be classified by type in several ways: The user respiratory interface is the delivery system by which the breathing apparatus guides the breathing gas flow to and from the user. Some form of facepiece, hood or helmet is usual, but for some medical interventions an invasive method may be necessary. Any given unit is a member of several types. The well-known recreational scuba set

220-491: A space suit . Actual usage varies, and breathing apparatus, breathing set, ventilator and respirator have similar and overlapping meanings which vary depending on the sources chosen. Breathing set appears to be a secondary synonym for breathing apparatus, as internet searches appear to all be redirected to breathing apparatus. According to Merriam-Webster , a ventilator can be a medical device to provide artificially assisted respiration, or equipment to circulate fresh air through

330-436: A toxic concentration of oxygen . Most breathing sets for hyperbaric use are ambient pressure underwater breathing apparatus, but breathing apparatus may be necessary in a pressurised tunnel or caisson due to contamination by hazardous materials. Minor leakage to the environment is usually of little importance. Open and closed circuit, self-contained, and remotely supplied systems are all in common use, but gas composition choice

440-422: A bite-grip, and sealed by the lips, is common in scuba equipment, snorkels , and some types of escape breathing apparatus. A mouthpiece is simple and effective, with minimal dead space, and reliably seals without need for adjustment, but must be actively held in place by the user, and can cause jaw fatigue over long periods. A mouthpiece retaining strap may be used to reduce jaw fatigue and the risk of losing grip on

550-401: A combination of ambient atmosphere and another of these sources. When using a pressurised gas supply, the breathing gas must be supplied to the respiratory interface at a suitable pressure for inhalation, which is close to ambient pressure. This is generally done by a breathing gas regulator, a pressure reduction regulator , which reduces the gas supply pressure from the supply line. Exhalation

660-472: A complex expression depends on its parts. Part of this process involves the distinction between sense and reference . Sense is given by the ideas and concepts associated with an expression while reference is the object to which an expression points. Semantics contrasts with syntax , which studies the rules that dictate how to create grammatically correct sentences, and pragmatics , which investigates how people use language in communication. Lexical semantics

770-493: A different context. For example, the reference of the word here depends on the location in which it is used. A closely related approach is possible world semantics, which allows expressions to refer not only to entities in the actual world but also to entities in other possible worlds. According to this view, expressions like the first man to run a four-minute mile refer to different persons in different worlds. This view can also be used to analyze sentences that talk about what

880-440: A different sense have the same referent. For instance, the sentence "the morning star is the evening star" is informative and people can learn something from it. The sentence "the morning star is the morning star", by contrast, is an uninformative tautology since the expressions are identical not only on the level of reference but also on the level of sense. Compositionality is a key aspect of how languages construct meaning. It

990-411: A facepiece, is a component which covers the mouth and nose, sometimes also the eyes and other parts of the face, and may seal against the face. A breathing mask is usually effective, allows mouth and nose breathing, and can usually be sealed adequately without effort by the user. A wide range of designs are available depending on the application. The disadvantages are that the user cannot eat or drink while

1100-533: A hose to supply gas from the supply panel and in some cases a return hose for the exhaled gas. Remotely supplied applications include: Self-contained applications include: The user respiratory interface, also commonly referred to as the facepiece, is the delivery system by which the breathing apparatus controls breathing gas flow to and from the user. The choice of interface type and the fit can significantly influence convenience, effectiveness, comfort, and sometimes safety. Several types are in use: A nasal cannula

1210-413: A more complex meaning structure. In the expression "Beethoven likes Schubert", the verb like connects a liker to the object of their liking. Other sentence parts modify meaning rather than form new connections. For instance, the adjective red modifies the color of another entity in the expression red car . A further compositional device is variable binding, which is used to determine the reference of

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1320-525: A motor to pass ambient air through the filter, or unpowered, relying on the wearer's breathing to draw ambient air through the filter. The distinguishing features of a respirator in this context appear to be that the air is not significantly compressed at any stage, is filtered, and is at approximately ambient pressure. The HSE definition for breathing apparatus is that they use a supply of breathing quality gas from an independent source, such as air compressors or compressed gas cylinders. In this case compression of

1430-414: A particular language. Some semanticists also include the study of lexical units other than words in the field of lexical semantics. Compound expressions like being under the weather have a non-literal meaning that acts as a unit and is not a direct function of its parts. Another topic concerns the meaning of morphemes that make up words, for instance, how negative prefixes like in- and dis- affect

1540-413: A particular language. The same symbol may refer to one object in one language, to another object in a different language, and to no object in another language. Many other concepts are used to describe semantic phenomena. The semantic role of an expression is the function it fulfills in a sentence. In the sentence "the boy kicked the ball", the boy has the role of the agent who performs an action. The ball

1650-408: A person to function in irrespirable or poisonous gases or fluids; contains a supply of oxygen and a regenerator which removes the carbon dioxide exhaled", which is the description of any type or application of rebreather. The US Occupational Safety and Health Administration (OSHA) uses the source of the breathing gas to distinguish between types of breathing apparatus, and considers respirators to be

1760-430: A slight overpressure, also known as positive pressure , to prevent contamination by ambient gas, as leakage from the breathing set is generally less harmful than breathing the ambient gas. This subclass includes both self-contained and airline supplied units, and self-contained units may use rebreather technology to extend gas endurance. A breathing set intended for use in hyperbaric environments must not supply gas with

1870-405: A small reservoir below the nose during exhalation and delivers it in a bolus at the beginning of the next inhalation, which ensures that most of it reaches the parts of the lung in which gas exchange occurs, and little is wasted in dead space. A nasal mask covers the nose and seals against the upper lip, the sides of the nose, and the bridge of the nose. A nasal pillow mask seals on the rim of

1980-409: A space suit is circulated by an electric fan). When powered by breathing effort, rebreather units will have an elevated work of breathing, particularly with high gas densities at great depth, which is a limiting factor for diving rebreathers, even when the diluent is helium. Breathing apparatus can also be categorised as self-contained, where everything is carried by the user, or remotely supplied, with

2090-549: A space, while a respirator is usually a mask worn to protect the user from particulate contaminants in the air, but can also mean a device for providing artificial respiration. The usage in the sense of a filtering mask dates to the early 19th century and the artificial respiration sense dates to the second half of the 19th century, so both are well established. The UK Health and Safety Executive (HSE) distinguishes between respirators and breathing apparatus. Respirators are described as filtering devices , which may be powered, using

2200-445: A speaker remains silent on a certain topic. A closely related distinction by the semiotician Charles W. Morris holds that semantics studies the relation between words and the world, pragmatics examines the relation between words and users, and syntax focuses on the relation between different words. Semantics is related to etymology , which studies how words and their meanings changed in the course of history. Another connected field

2310-438: A strict distinction between meaning and syntax and by relying on various formal devices to explore the relation between meaning and cognition. Computational semantics examines how the meaning of natural language expressions can be represented and processed on computers. It often relies on the insights of formal semantics and applies them to problems that can be computationally solved. Some of its key problems include computing

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2420-459: A strong sense, the principle of compositionality states that the meaning of a complex expression is not just affected by its parts and how they are combined but fully determined this way. It is controversial whether this claim is correct or whether additional aspects influence meaning. For example, context may affect the meaning of expressions; idioms like " kick the bucket " carry figurative or non-literal meanings that are not directly reducible to

2530-508: A term. For example, the last part of the expression "the woman who likes Beethoven" specifies which woman is meant. Parse trees can be used to show the underlying hierarchy employed to combine the different parts. Various grammatical devices, like the gerund form, also contribute to meaning and are studied by grammatical semantics. Formal semantics uses formal tools from logic and mathematics to analyze meaning in natural languages. It aims to develop precise logical formalisms to clarify

2640-407: A text that come before and after it. Context affects the meaning of various expressions, like the deictic expression here and the anaphoric expression she . A syntactic environment is extensional or transparent if it is always possible to exchange expressions with the same reference without affecting the truth value of the sentence. For example, the environment of the sentence "the number 8

2750-421: A type or class of breathing apparatus: An atmosphere-supplying respirator is a breathing apparatus that supplies the user with breathing gas from a source independent of the ambient atmosphere, such as supplied-air respirators (SARs) and self-contained breathing apparatus (SCBA). A self-contained breathing apparatus (SCBA) is a type of atmosphere-supplying breathing apparatus in which the breathing gas source

2860-457: A uniform signifying rank , and the presence of vultures indicating a nearby animal carcass. Semantics further contrasts with pragmatics , which is interested in how people use language in communication. An expression like "That's what I'm talking about" can mean many things depending on who says it and in what situation. Semantics is interested in the possible meanings of expressions: what they can and cannot mean in general. In this regard, it

2970-427: A word means by looking at its letters and one needs to consult a dictionary instead. Compositionality is often used to explain how people can formulate and understand an almost infinite number of meanings even though the amount of words and cognitive resources is finite. Many sentences that people read are sentences that they have never seen before and they are nonetheless able to understand them. When interpreted in

3080-484: Is hermeneutics , which is the art or science of interpretation and is concerned with the right methodology of interpreting text in general and scripture in particular. Metasemantics examines the metaphysical foundations of meaning and aims to explain where it comes from or how it arises. The word semantics originated from the Ancient Greek adjective semantikos , meaning 'relating to signs', which

3190-400: Is 8. Semanticists commonly distinguish the language they study, called object language, from the language they use to express their findings, called metalanguage . When a professor uses Japanese to teach their student how to interpret the language of first-order logic then the language of first-order logic is the object language and Japanese is the metalanguage. The same language may occupy

3300-529: Is a derivative of sēmeion , the noun for ' sign '. It was initially used for medical symptoms and only later acquired its wider meaning regarding any type of sign, including linguistic signs. The word semantics entered the English language from the French term semantique , which the linguist Michel Bréal first introduced at the end of the 19th century. Semantics studies meaning in language, which

3410-441: Is a self-contained, open circuit, demand supplied, high pressure stored air, ambient pressure, underwater diving type, delivered through a bite-grip secured mouthpiece. Semantically , the term breathing apparatus implies any set of equipment and materials specifically intended to enable or facilitate breathing, which could include equipment as basic as a snorkel or artificial airway , or as complex as an anaesthetic machine or

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3520-573: Is a type of respiratory interface that completely covers the head and neck, and optionally the shoulders or upper torso, with a loose-fitting bag, which may have a neck seal or be relatively close fitting at the neck or shoulders. They are used in escape breathing apparatus of several kinds ( escape hoods ), and as a route for supplementary oxygen ( oxygen hoods ). Breathing hoods with full length visors are commonly used with free-flow supplied air respirators for industrial work like in spray painting, boatbuilding, and woodworking workshops. A breathing helmet

3630-577: Is and how it arises. It investigates how expressions are built up from different layers of constituents, like morphemes , words , clauses , sentences , and texts , and how the meanings of the constituents affect one another. Semantics can focus on a specific language, like English, but in its widest sense, it investigates meaning structures relevant to all languages. As a descriptive discipline, it aims to determine how meaning works without prescribing what meaning people should associate with particular expressions. Some of its key questions are "How do

3740-409: Is any breathing apparatus that does not recycle any of the breathing gas, and discharges it all to the surroundings. Supply can be further classified as positive and negative pressure systems, based on the pressure maintained when flow has stopped, and whether the breathing gas pressure in the apparatus ever drops below ambient pressure. Open circuit systems without mixing during delivery are simple and

3850-439: Is carried by the user. A supplied-air respirator (SAR), or airline respirator, is a type of atmosphere-supplying breathing apparatus which uses a hose to supply breathing gas from a source which is not carried by the user. An air-purifying respirator is a breathing apparatus which uses a filter, cartridge, or canister, to remove specific air contaminants by passing ambient air through the air-purifying component. No distinction

3960-445: Is complicated by the possibility of oxygen toxicity and decompression requirements. The possibilities of nitrogen narcosis and excessive gas density causing unacceptably high work of breathing make the use of helium as a diluent necessary for use at greater depths. The large range of pressures possible complicate decompression necessary to avoid decompression sickness , and the use of special gas mixtures to accelerate decompression

4070-426: Is created through the combination of expressions belonging to different syntactic categories. Dynamic semantics is a subfield of formal semantics that focuses on how information grows over time. According to it, "meaning is context change potential": the meaning of a sentence is not given by the information it contains but by the information change it brings about relative to a context. Cognitive semantics studies

4180-445: Is described but an experience takes place, like when a girl sees a bird. In this case, the girl has the role of the experiencer. Other common semantic roles are location, source, goal, beneficiary, and stimulus. Lexical relations describe how words stand to one another. Two words are synonyms if they share the same or a very similar meaning, like car and automobile or buy and purchase . Antonyms have opposite meanings, such as

4290-408: Is even" is extensional because replacing the expression the number 8 with the number of planets in the solar system does not change its truth value. For intensional or opaque contexts , this type of substitution is not always possible. For instance, the embedded clause in "Paco believes that the number 8 is even" is intensional since Paco may not know that the number of planets in the solar system

4400-399: Is fairly common. This either requires the diver to use several mixtures at different depths which could be toxic if used at the wrong depth, or for closed circuit apparatus which provides reliable control and monitoring of the gas mixture. As a malfunction which cuts off breathing gas supply to a diver at depth could be rapidly fatal, bailout breathing apparatus may be carried in addition to

4510-514: Is interested in how meanings evolve and change because of cultural phenomena associated with politics , religion, and customs . For example, address practices encode cultural values and social hierarchies, as in the difference of politeness of expressions like tu and usted in Spanish or du and Sie in German in contrast to English, which lacks these distinctions and uses

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4620-404: Is known as a constant flow, continuous flow, or free-flow system. The user inhales from the stream of fresh gas passing the face, and exhales back into the same stream. Supply rate must be sufficient that at reasonably foreseeable work rates, the inhaled gas does not include too much of the previously exhaled gas. This is simple, but wasteful of supplied gas. The gas can be supplied on demand, when

4730-454: Is limited to the meaning of linguistic expressions. It concerns how signs are interpreted and what information they contain. An example is the meaning of words provided in dictionary definitions by giving synonymous expressions or paraphrases, like defining the meaning of the term ram as adult male sheep . There are many forms of non-linguistic meaning that are not examined by semantics. Actions and policies can have meaning in relation to

4840-478: Is made based on the mechanism of passing the air through the purifying component – it may be the lungs of the user or a mechanical device. The breathing gas source may be the ambient atmosphere, compressed air supplied from a low pressure compressor in real time, oxygen enriched air supplied from an oxygen concentrator, high-pressure stored compressed air, supercritical compressed air , oxygen or blended gas mixtures, liquid oxygen , chemically generated oxygen, or

4950-446: Is possible or what is necessary: possibility is what is true in some possible worlds while necessity is what is true in all possible worlds. Ideational theories, also called mentalist theories, are not primarily interested in the reference of expressions and instead explain meaning in terms of the mental states of language users. One historically influential approach articulated by John Locke holds that expressions stand for ideas in

5060-480: Is relatively unobtrusive and is widely used for supplemental oxygen. The basic version is used to deliver continuous flow supplemental oxygen at rates from 1 to 6 litres per minute. It has two short prongs that fit into the nostrils for delivery, that are connected to a common tube, which is usually hooked over the ears for support. The more complex reservoir cannula is an oxygen conserving supplemental oxygen administration device which accumulates constant flow oxygen in

5170-531: Is required, it may allow a large saving of gas and be much simpler or lighter than the equivalent open circuit option. Rebreather systems can be closed or semi-closed circuit, have a pendulum or loop flow path configuration, and the gas can be circulated by the breathing of the user through non-return valves, (almost all self-contained units), by the energy of the injected fresh gas, (Dräger Modell 1915 "Bubikopf", DM20 and DM40, and US Navy Mk V helium helmet gas extenders,), or by an external power input (the oxygen in

5280-430: Is sometimes defined as the study of context-independent meaning. Pragmatics examines which of these possible meanings is relevant in a particular case. In contrast to semantics, it is interested in actual performance rather than in the general linguistic competence underlying this performance. This includes the topic of additional meaning that can be inferred even though it is not literally expressed, like what it means if

5390-444: Is sometimes divided into two complementary approaches: semasiology and onomasiology . Semasiology starts from words and examines what their meaning is. It is interested in whether words have one or several meanings and how those meanings are related to one another. Instead of going from word to meaning, onomasiology goes from meaning to word. It starts with a concept and examines what names this concept has or how it can be expressed in

5500-504: Is sometimes understood as a mental phenomenon that helps people identify the objects to which an expression refers. Some semanticists focus primarily on sense or primarily on reference in their analysis of meaning. To grasp the full meaning of an expression, it is usually necessary to understand both to what entities in the world it refers and how it describes them. The distinction between sense and reference can explain identity statements , which can be used to show how two expressions with

5610-567: Is sufficient that a pressure suit is not needed. Both rebreather and open circuit equipment have been used in this application, where either pure oxygen or supplemental oxygen is provided by the equipment. Minor leakage in either direction usually only affects efficiency and gas endurance, as the ambient air is usually only hypoxic due to low ambient pressure. Breathing apparatus are used for mine escape and rescue, firefighting, or working in hypoxic or toxic atmospheres at pressures near to normal atmospheric pressure . These may supply breathing gas at

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5720-413: Is the branch of semantics that studies word meaning . It examines whether words have one or several meanings and in what lexical relations they stand to one another. Phrasal semantics studies the meaning of sentences by exploring the phenomenon of compositionality or how new meanings can be created by arranging words. Formal semantics relies on logic and mathematics to provide precise frameworks of

5830-416: Is the idea that the meaning of a complex expression is a function of the meanings of its parts. It is possible to understand the meaning of the sentence "Zuzana owns a dog" by understanding what the words Zuzana , owns , a and dog mean and how they are combined. In this regard, the meaning of complex expressions like sentences is different from word meaning since it is normally not possible to deduce what

5940-419: Is the object to which the expression points. The sense of an expression is the way in which it refers to that object or how the object is interpreted. For example, the expressions morning star and evening star refer to the same planet, just like the expressions 2 + 2 and 3 + 1 refer to the same number. The meanings of these expressions differ not on the level of reference but on the level of sense. Sense

6050-404: Is the theme or patient of this action as something that does not act itself but is involved in or affected by the action. The same entity can be both agent and patient, like when someone cuts themselves. An entity has the semantic role of an instrument if it is used to perform the action, for instance, when cutting something with a knife then the knife is the instrument. For some sentences, no action

6160-404: Is true. Many related disciplines investigate language and meaning. Semantics contrasts with other subfields of linguistics focused on distinct aspects of language. Phonology studies the different types of sounds used in languages and how sounds are connected to form words while syntax examines the rules that dictate how to arrange words to create sentences. These divisions are reflected in

6270-450: Is used if the different meanings are closely related to one another, like the meanings of the word head , which can refer to the topmost part of the human body or the top-ranking person in an organization. The meaning of words can often be subdivided into meaning components called semantic features . The word horse has the semantic feature animate but lacks the semantic feature human . It may not always be possible to fully reconstruct

6380-495: Is usual to use oxygen rebreather systems, as they are relatively safe, simple and efficient compared to open circuit, and do not inherently affect suit internal pressure. Liquid air has also been used for space suits, which implies an internal suit pressure close to normal atmospheric pressure, and open circuit. Leakage to or from the outside environment generally indicates a system failure and an emergency. Positive and negative pressure systems can have slightly different meanings in

6490-409: Is usually defined as a rigid respiratory user interface covering the head that also provides head protection against impact and penetration. In medical terminology, a breathing helmet is synonymous with a breathing hood, and need not have any rigid protective structure. Breathing apparatus may be used in various pressure regimes: hyperbaric for diving, tunneling, and caisson work, normobaric where

6600-470: Is usually to the surroundings at ambient pressure, but in special cases such as built-in breathing systems and gas reclaim systems , it may be exhausted to a significantly lower pressure, sometimes at a remote location, and may require a back-pressure regulator to do this safely. Supplied gas breathing apparatus can be categorised by how the gas is supplied to the user. There are several combinations of options The gas can be supplied continuously, in what

6710-399: The use theory , and inferentialist semantics . The study of semantic phenomena began during antiquity but was not recognized as an independent field of inquiry until the 19th century. Semantics is relevant to the fields of formal logic, computer science , and psychology . Semantics is the study of meaning in languages . It is a systematic inquiry that examines what linguistic meaning

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6820-598: The vocabulary as a whole. This includes the study of lexical relations between words, such as whether two terms are synonyms or antonyms. Lexical semantics categorizes words based on semantic features they share and groups them into semantic fields unified by a common subject. This information is used to create taxonomies to organize lexical knowledge, for example, by distinguishing between physical and abstract entities and subdividing physical entities into stuff and individuated entities . Further topics of interest are polysemy, ambiguity, and vagueness . Lexical semantics

6930-422: The ambient atmosphere is unbreathable, or supplemental oxygen is needed for medical reasons, and hypobaric at high altitudes and in space. High altitude breathing apparatus is used for unpressurised (ambient pressure) aeronautical and mountaineering activities where the oxygen content of the natural atmosphere is insufficient for maintaining physical activity, consciousness, or life, but the atmospheric pressure

7040-413: The breathing space. This also has the physiological effect of assisting inhalation and resisting exhalation, but should not affect the total work of breathing. Negative pressure means that the pressure inside the facepiece is lower than the ambient pressure outside the facepiece at some point during inhalation, and a good seal on the facepiece is required to prevent leakage of the ambient gas or liquid into

7150-407: The breathing space. This pressure offset is usually constant over all or several breaths, depending on the cause, and has the opposite effect of assisting exhalation and resisting inhalation, also with no net effect on the total work of breathing. Semantically Semantics is the study of linguistic meaning . It examines what meaning is, how words get their meaning, and how the meaning of

7260-486: The carbon dioxide from, and add oxygen to, a user's exhaled breath, allowing unused oxygen and diluent (if present) to be recycled. A rebreather system may be used for any application of a supplied gas breathing set. It may be more complex than open circuit if the mixture must be controlled, and for short endurance applications may be heavier. There may be a greater fire hazard due to high oxygen concentration. In other applications, when long endurance and reasonably light weight

7370-475: The chin, and the full-face mask covers the eyes as well as the nose and mouth, and can have a dead space so large that an inner orinasal mask is provided to reduce the dead space. A diving half-mask used in scuba and freediving covers the eyes and nose, and is not breathing apparatus. A full-face mask is generally only used when including the eyes in the protected space is necessary, and often includes an inner orinasal mask to reduce dead space. A breathing hood

7480-420: The cognitive conceptual structures of humans are universal or relative to their linguistic background. Another research topic concerns the psychological processes involved in the application of grammar. Other investigated phenomena include categorization, which is understood as a cognitive heuristic to avoid information overload by regarding different entities in the same way, and embodiment , which concerns how

7590-454: The conditions under which it would be true. This can happen even if one does not know whether the conditions are fulfilled. The semiotic triangle , also called the triangle of meaning, is a model used to explain the relation between language, language users, and the world, represented in the model as Symbol , Thought or Reference , and Referent . The symbol is a linguistic signifier , either in its spoken or written form. The central idea of

7700-472: The context of breathing apparatus depending on whether the context is medical or non-medical applications. In this context these terms refer to the protection of the breathing circuit against leakage of contaminants. Positive pressure means that the area around the mouth or nose inside the facepiece remains slightly higher than the ambient pressure outside the breathing apparatus facepiece at all times while in use, so that ambient gas or liquid cannot leak into

7810-408: The context, like the deictic terms here and I . To avoid these problems, referential theories often introduce additional devices. Some identify meaning not directly with objects but with functions that point to objects. This additional level has the advantage of taking the context of an expression into account since the same expression may point to one object in one context and to another object in

7920-478: The contrast between alive and dead or fast and slow . One term is a hyponym of another term if the meaning of the first term is included in the meaning of the second term. For example, ant is a hyponym of insect . A prototype is a hyponym that has characteristic features of the type it belongs to. A robin is a prototype of a bird but a penguin is not. Two words with the same pronunciation are homophones like flour and flower , while two words with

8030-399: The corresponding physical object. The relation is only established indirectly through the mind of the language user. When they see the symbol, it evokes a mental image or a concept, which establishes the connection to the physical object. This process is only possible if the language user learned the meaning of the symbol before. The meaning of a specific symbol is governed by the conventions of

8140-541: The fact that it is possible to master some aspects of a language while lacking others, like when a person knows how to pronounce a word without knowing its meaning. As a subfield of semiotics, semantics has a more narrow focus on meaning in language while semiotics studies both linguistic and non-linguistic signs. Semiotics investigates additional topics like the meaning of non-verbal communication , conventional symbols , and natural signs independent of human interaction. Examples include nodding to signal agreement, stripes on

8250-423: The foreground while the base is the background that provides the context of this aspect without being at the center of attention. For example, the profile of the word hypotenuse is a straight line while the base is a right-angled triangle of which the hypotenuse forms a part. Cognitive semantics further compares the conceptual patterns and linguistic typologies across languages and considers to what extent

8360-523: The gas supplied is consistent and reliable. Both constant flow and demand supply can also provide gas from two sources, one of them being the ambient atmosphere, in what is generally referred to as supplemental oxygen provision, frequently used for medical purposes where the user is at risk for medical hypoxia, and at high altitudes where the oxygen partial pressure is naturally low. Closed and semi-closed circuit breathing sets, also known as rebreathers and gas extenders , are breathing apparatus that absorb

8470-408: The goal they serve. Fields like religion and spirituality are interested in the meaning of life , which is about finding a purpose in life or the significance of existence in general. Linguistic meaning can be analyzed on different levels. Word meaning is studied by lexical semantics and investigates the denotation of individual words. It is often related to concepts of entities, like how

8580-453: The language user's bodily experience affects the meaning of expressions. Frame semantics is an important subfield of cognitive semantics. Its central idea is that the meaning of terms cannot be understood in isolation from each other but needs to be analyzed on the background of the conceptual structures they depend on. These structures are made explicit in terms of semantic frames. For example, words like bride, groom, and honeymoon evoke in

8690-435: The mask is in place, and some models may interfere with speech, while others may have relatively large dead space. Three basic configurations are distinguished by the area they cover. The orinasal mask, also called oro-nasal, oral-nasal, or quarter mask, covers the mouth and nostrils and seals to the front of the face on the bridge and sides of the nose and mouth and the chin with little dead space. The half-mask extends below

8800-457: The meaning of a word by identifying all its semantic features. A semantic or lexical field is a group of words that are all related to the same activity or subject. For instance, the semantic field of cooking includes words like bake , boil , spice , and pan . The context of an expression refers to the situation or circumstances in which it is used and includes time, location, speaker, and audience. It also encompasses other passages in

8910-446: The meaning of an expression is the part of reality to which it points. Ideational theories identify meaning with mental states like the ideas that an expression evokes in the minds of language users. According to causal theories, meaning is determined by causes and effects, which behaviorist semantics analyzes in terms of stimulus and response. Further theories of meaning include truth-conditional semantics , verificationist theories,

9020-492: The meaning of complex expressions by analyzing their parts, handling ambiguity, vagueness, and context-dependence, and using the extracted information in automatic reasoning . It forms part of computational linguistics , artificial intelligence , and cognitive science . Its applications include machine learning and machine translation . Cultural semantics studies the relation between linguistic meaning and culture. It compares conceptual structures in different languages and

9130-407: The meaning of particular expressions, like the semantics of the word fairy . As a field of inquiry, semantics has both an internal and an external side. The internal side is interested in the connection between words and the mental phenomena they evoke, like ideas and conceptual representations. The external side examines how words refer to objects in the world and under what conditions a sentence

9240-655: The meaning of the name George Washington is the person with this name. General terms refer not to a single entity but to the set of objects to which this term applies. In this regard, the meaning of the term cat is the set of all cats. Similarly, verbs usually refer to classes of actions or events and adjectives refer to properties of individuals and events. Simple referential theories face problems for meaningful expressions that have no clear referent. Names like Pegasus and Santa Claus have meaning even though they do not point to existing entities. Other difficulties concern cases in which different expressions are about

9350-421: The meaning of the words they are part of, as in inanimate and dishonest . Phrasal semantics studies the meaning of sentences. It relies on the principle of compositionality to explore how the meaning of complex expressions arises from the combination of their parts. The different parts can be analyzed as subject , predicate , or argument . The subject of a sentence usually refers to a specific entity while

9460-413: The meanings of their parts. Truth is a property of statements that accurately present the world and true statements are in accord with reality . Whether a statement is true usually depends on the relation between the statement and the rest of the world. The truth conditions of a statement are the way the world needs to be for the statement to be true. For example, it belongs to the truth conditions of

9570-492: The meanings of words combine to create the meanings of sentences?", "How do meanings relate to the minds of language users, and to the things words refer to?", and "What is the connection between what a word means, and the contexts in which it is used?". The main disciplines engaged in semantics are linguistics , semiotics , and philosophy . Besides its meaning as a field of inquiry, semantics can also refer to theories within this field, like truth-conditional semantics , and to

9680-467: The mind the frame of marriage. Conceptual semantics shares with cognitive semantics the idea of studying linguistic meaning from a psychological perspective by examining how humans conceptualize and experience the world. It holds that meaning is not about the objects to which expressions refer but about the cognitive structure of human concepts that connect thought, perception, and action. Conceptual semantics differs from cognitive semantics by introducing

9790-448: The model is that there is no direct relation between a linguistic expression and what it refers to, as was assumed by earlier dyadic models. This is expressed in the diagram by the dotted line between symbol and referent. The model holds instead that the relation between the two is mediated through a third component. For example, the term apple stands for a type of fruit but there is no direct connection between this string of letters and

9900-457: The mouthpiece in an emergency. A mouthpiece only allows mouth breathing of the delivered gas, and it may be necessary to block the nose to prevent bypass. A mouthpiece makes intelligible speech difficult or impossible, and eating or drinking require temporary removal. An oral mask fits inside the mouth between the teeth and lips, with a guide to prevent the tongue from obstructing the airway. They are not often used. A breathing mask, also called

10010-513: The nostrils. It is used in stable patients with sleep-disordered breathing. An artificial airway uses a medical device to provide a patent airway. This requires intervention by a competent person, and may be supraglottic, infraglottic, or surgically placed. These applications are mostly used in emergency medicine and surgery. Devices in this class include laryngeal mask airways , esophageal-tracheal combitubes , endotracheal tubes , and tracheostomy tubes . A mouthpiece , usually held in place by

10120-564: The predicate describes a feature of the subject or an event in which the subject participates. Arguments provide additional information to complete the predicate. For example, in the sentence "Mary hit the ball", Mary is the subject, hit is the predicate, and the ball is an argument. A more fine-grained categorization distinguishes between different semantic roles of words, such as agent, patient, theme, location, source, and goal. Verbs usually function as predicates and often help to establish connections between different expressions to form

10230-444: The primary gas supply. At extremes of ambient pressure, the user must be isolated from the environment to survive, as in single atmosphere diving suits , where the occupant is kept at surface atmospheric pressure, isolated from the high ambient pressure of the deep underwater environment, and pressure suits and space suits where the interior of the suit is pressurised above the external environmental pressure. In these applications it

10340-401: The problem of meaning from a psychological perspective or how the mind of the language user affects meaning. As a subdiscipline of cognitive linguistics , it sees language as a wide cognitive ability that is closely related to the conceptual structures used to understand and represent the world. Cognitive semanticists do not draw a sharp distinction between linguistic knowledge and knowledge of

10450-601: The pronoun you in either case. Closely related fields are intercultural semantics, cross-cultural semantics, and comparative semantics. Pragmatic semantics studies how the meaning of an expression is shaped by the situation in which it is used. It is based on the idea that communicative meaning is usually context-sensitive and depends on who participates in the exchange, what information they share, and what their intentions and background assumptions are. It focuses on communicative actions, of which linguistic expressions only form one part. Some theorists include these topics within

10560-497: The public meaning that expressions have, like the meaning found in general dictionary definitions. Speaker meaning, by contrast, is the private or subjective meaning that individuals associate with expressions. It can diverge from the literal meaning, like when a person associates the word needle with pain or drugs. Meaning is often analyzed in terms of sense and reference , also referred to as intension and extension or connotation and denotation . The referent of an expression

10670-450: The relation between expressions and their denotation. One of its key tasks is to provide frameworks of how language represents the world, for example, using ontological models to show how linguistic expressions map to the entities of that model. A common idea is that words refer to individual objects or groups of objects while sentences relate to events and states. Sentences are mapped to a truth value based on whether their description of

10780-489: The relation between language and meaning. Cognitive semantics examines meaning from a psychological perspective and assumes a close relation between language ability and the conceptual structures used to understand the world. Other branches of semantics include conceptual semantics , computational semantics , and cultural semantics. Theories of meaning are general explanations of the nature of meaning and how expressions are endowed with it. According to referential theories ,

10890-403: The role of object language and metalanguage at the same time. This is the case in monolingual English dictionaries , in which both the entry term belonging to the object language and the definition text belonging to the metalanguage are taken from the English language. Lexical semantics is the sub-field of semantics that studies word meaning. It examines semantic aspects of individual words and

11000-402: The same entity. For instance, the expressions Roger Bannister and the first man to run a four-minute mile refer to the same person but do not mean exactly the same thing. This is particularly relevant when talking about beliefs since a person may understand both expressions without knowing that they point to the same entity. A further problem is given by expressions whose meaning depends on

11110-412: The same proposition, like the English sentence "the tree is green" and the German sentence "der Baum ist grün" . Utterance meaning is studied by pragmatics and is about the meaning of an expression on a particular occasion. Sentence meaning and utterance meaning come apart in cases where expressions are used in a non-literal way, as is often the case with irony . Semantics is primarily interested in

11220-427: The same spelling are homonyms , like a bank of a river in contrast to a bank as a financial institution. Hyponymy is closely related to meronymy , which describes the relation between part and whole. For instance, wheel is a meronym of car . An expression is ambiguous if it has more than one possible meaning. In some cases, it is possible to disambiguate them to discern the intended meaning. The term polysemy

11330-440: The scope of semantics while others consider them part of the distinct discipline of pragmatics. Theories of meaning explain what meaning is, what meaning an expression has, and how the relation between expression and meaning is established. Referential theories state that the meaning of an expression is the entity to which it points. The meaning of singular terms like names is the individual to which they refer. For example,

11440-410: The sentence "it is raining outside" that raindrops are falling from the sky. The sentence is true if it is used in a situation in which the truth conditions are fulfilled, i.e., if there is actually rain outside. Truth conditions play a central role in semantics and some theories rely exclusively on truth conditions to analyze meaning. To understand a statement usually implies that one has an idea about

11550-475: The speaker's mind. According to this view, the meaning of the word dog is the idea that people have of dogs. Language is seen as a medium used to transfer ideas from the speaker to the audience. After having learned the same meaning of signs, the speaker can produce a sign that corresponds to the idea in their mind and the perception of this sign evokes the same idea in the mind of the audience. Compressed air Too Many Requests If you report this error to

11660-512: The supply gas at some stage is implied. Both respirators and breathing apparatus are classed as respiratory protective equipment by the HSE. Vocabulary.com describes a breathing apparatus as "a device that facilitates breathing in cases of respiratory failure", which is a functional description of a medical ventilator, or a resuscitator. McGraw-Hill Dictionary of Scientific & Technical Terms defines breathing apparatus as "An appliance that enables

11770-471: The user inhales, using the pressure drop at the start of inhalation to control the opening of a demand valve, and the automatically stops when there is no demand. This is more conservative in gas usage, but has a higher work of breathing. It requires a facepiece that seals moderately well to the user, with a small internal volume to limit dead space. Some demand supplied breathing apparatus can be swithced to continuous flow mode. Open circuit breathing apparatus

11880-407: The word dog is associated with the concept of the four-legged domestic animal. Sentence meaning falls into the field of phrasal semantics and concerns the denotation of full sentences. It usually expresses a concept applying to a type of situation, as in the sentence "the dog has ruined my blue skirt". The meaning of a sentence is often referred to as a proposition . Different sentences can express

11990-432: The world and see them instead as interrelated phenomena. They study how the interaction between language and human cognition affects the conceptual organization in very general domains like space, time, causation, and action. The contrast between profile and base is sometimes used to articulate the underlying knowledge structure. The profile of a linguistic expression is the aspect of the knowledge structure that it brings to

12100-542: The world is in correspondence with its ontological model. Formal semantics further examines how to use formal mechanisms to represent linguistic phenomena such as quantification , intensionality , noun phrases , plurals , mass terms, tense , and modality . Montague semantics is an early and influential theory in formal semantics that provides a detailed analysis of how the English language can be represented using mathematical logic. It relies on higher-order logic , lambda calculus , and type theory to show how meaning

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