Humeanism

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Humeanism refers to the philosophy of David Hume and to the tradition of thought inspired by him. Hume was an influential Scottish philosopher well known for his empirical approach, which he applied to various fields in philosophy. In the philosophy of science, he is notable for developing the regularity theory of causation, which in its strongest form states that causation is nothing but constant conjunction of certain types of events without any underlying forces responsible for this regularity of conjunction. This is closely connected to his metaphysical thesis that there are no necessary connections between distinct entities. The Humean theory of action defines actions as bodily behavior caused by mental states and processes without the need to refer to an agent responsible for this. The slogan of Hume's theory of practical reason is that "reason is...the slave of the passions". It restricts the sphere of practical reason to instrumental rationality concerning which means to employ to achieve a given end. But it denies reason a direct role regarding which ends to follow. Central to Hume's position in metaethics is the is-ought distinction. It states that is-statements, which concern facts about the natural world, do not imply ought-statements, which are moral or evaluative claims about what should be done or what has value. In philosophy of mind, Hume is well known for his development of the bundle theory of the self. It states that the self is to be understood as a bundle of mental states and not as a substance acting as the bearer of these states, as is the traditional conception. Many of these positions were initially motivated by Hume's empirical outlook. It emphasizes the need to ground one's theories in experience and faults the opposed theories for failing to do so. But many philosophers within the Humean tradition have gone beyond these methodological restrictions and have drawn various metaphysical conclusions from Hume's ideas.

Contents

• 1 Causality and necessity
• 2 Theory of action
• 3 Practical reason
• 4 Metaethics
• 5 Bundle theory of the self
• 6 References

Causality and necessity

Main article: Humean definition of causality

Causality is usually understood as a relation between two events where the earlier event is responsible for bringing about or necessitating the later event. Hume's account of causality has been influential. His first question is how to categorize causal relations. On his view, they belong either to relations of ideas or matters of fact. This distinction is referred to as Hume's fork. Relations of ideas involve necessary connections that are knowable apriori independently of experience. Matters of fact, on the other hand, concern contingent propositions about the world knowable only a posteriori through perception and memory. Causal relations fall under the category of matters of facts, according to Hume, since it is conceivable that they do not obtain, which would not be the case if they were necessary. For Hume's empiricist outlook, this means that causal relations should be studied by attending to sensory experience. The problem with this is that the causal relation itself is never given this way. Through visual perception, for example, we can know that a stone was first thrown in the direction of a window and that subsequently, the window broke. But we do not directly see that the throwing caused the breaking. This leads to Hume's skeptical conclusion: that, strictly speaking, we do not know that a causal relation was involved. Instead, we just assume it based on earlier experiences that had very similar chains of events as their contents. This results in a habit of expecting the later event given the impression of the earlier one. On the metaphysical level, this conclusion has often been interpreted as the thesis that causation is nothing but constant conjunction of certain types of events. This is sometimes termed the "simple regularity theory of causation".

A closely related metaphysical thesis is known as Hume's dictum: "[t]here is no object, which implies the existence of any other if we consider these objects in themselves". Jessica Wilson provides the following contemporary formulation: "[t]here are no metaphysically necessary connections between wholly distinct, intrinsically typed, entities". Hume's intuition motivating this thesis is that while experience presents us with certain ideas of various objects, it might as well have presented us with very different ideas. So when I perceive a bird on a tree, I might as well have perceived a bird without a tree or a tree without a bird. This is so because their essences do not depend upon one another. Followers and interpreters of Hume have sometimes used Hume's dictum as the metaphysical foundation of Hume's theory of causation. On this view, there cannot be any causal relation in a robust sense since this would involve one event necessitating another event, the possibility of which is denied by Hume's dictum.

Hume's dictum has been employed in various arguments in contemporary metaphysics. It can be used, for example, as an argument against nomological necessitarianism, the view that the laws of nature are necessary, i.e. are the same in all possible worlds. To see how this might work, consider the case of salt being thrown into a cup of water and subsequently dissolving. This can be described as a series of two events, a throwing-event and a dissolving-event. Necessitarians hold that all possible worlds with the throwing-event also contain a subsequent dissolving-event. But the two events are distinct entities, so according to Hume's dictum, it is possible to have one event without the other. David Lewis follows this line of thought in formulating his principle of recombination: "anything can coexist with anything else, at least provided they occupy distinct spatiotemporal positions. Likewise, anything can fail to coexist with anything else". Combined with the assumption that reality consists on the most fundamental level of nothing but a spatio-temporal distribution of local natural properties, this thesis is known as "Humean supervenience". It states that laws of nature and causal relations merely supervene on this distribution. An even wider application is to use Hume's dictum as an axiom of modality to determine which propositions or worlds are possible based on the notion of recombination.

Not all interpreters agree that the reductive metaphysical outlook on causation of the Humean tradition presented in the last paragraphs actually reflects Hume's own position. Some argue against the metaphysical aspect that Hume's view concerning causality remains within the field of epistemology as a skeptical position on the possibility of knowing about causal relations. Others, sometimes referred to as the "New Hume tradition", reject the reductive aspect by holding that Hume was, despite his skeptical outlook, a robust realist about causation.

Theory of action

Theories of action try to determine what actions are, specifically their essential features. One important feature of actions, which sets them apart from mere behavior, is that they are intentional or guided "under an idea". On this issue, Hume's analysis of action emphasizes the role of psychological faculties and states, like reasoning, sensation, memory, and passion. It is characteristic of his outlook that it manages to define action without reference to an agent. Agency arises instead from psychological states and processes like beliefs, desires and deliberation. Some actions are initiated upon concluding an explicit deliberation on which course of action to take. But for many other actions, this is not the case. Hume infers from this that "acts of the will" are not a necessary requirement for actions.

The most prominent philosopher of action in the Humean tradition is Donald Davidson. Following Hume in defining actions without reference to an agent, he holds that actions are bodily movements that are caused by intentions. The intentions themselves are explained in terms of beliefs and desires. For example, the action of flipping a light switch rests, on the one hand, on the agent's belief that this bodily movement would turn on the light and, on the other hand, on the desire to have light. According to Davidson, it is not just the bodily behavior that counts as the action but also the consequences that follow from it. So the movement of the finger flipping the switch is part of the action as well as the electrons moving through the wire and the light bulb turning on. Some consequences are included in the action even though the agent did not intend them to happen. It is sufficient that what the agent does "can be described under an aspect that makes it intentional". So, for example, if flipping the light switch alerts the burglar then alerting the burglar is part of the agent's actions.

One important objection to Davidson's and similar Humean theories focuses on the central role assigned to causation in defining action as bodily behavior caused by intention. The problem has been referred to as wayward or deviant causal chains. A causal chain is wayward if the intention caused its goal to realize but in a very unusual way that was not intended, e.g. because the skills of the agent are not exercised in the way planned. For example, a rock climber forms the intention to kill the climber below him by letting go of the rope. A wayward causal chain would be that, instead of opening the holding hand intentionally, the intention makes the first climber so nervous that the rope slips through his hand and thus leads to the other climber's death. Davidson addresses this issue by excluding cases of wayward causation from his account since they are not examples of intentional behavior in the strict sense. So bodily behavior only constitutes an action if it was caused by intentions in the right way. But this response has been criticized because of its vagueness since spelling out what "right way" means has proved rather difficult.

Practical reason

The slogan of Hume's theory of practical reason is that "reason is...the slave of the passions". It expresses the idea that it is the function of practical reason to find the means for realizing pre-given ends. Important for this issue is the distinction between means and ends. Ends are based on intrinsic desires, which are about things want for their own sake or are valuable in themselves. Means, on the other hand, are based on instrumental desires which want something for the sake of something else and thereby depend on other desires. So on this view, practical reason is about how to achieve something but it does not concern itself with what should be achieved. What should be achieved is determined by the agent's intrinsic desires. This may vary a lot from person to person since different people want very different things.

In contemporary philosophy, Hume's theory of practical reason is often understood in terms of norms of rationality. On the one hand, it is the thesis that we should be motivated to employ the means necessary for the ends we have. Failing to do so would be irrational. Expressed in terms of practical reasons, it states that if an agent has a reason to realize an end, this reason is transmitted from the end to the means, i.e. the agent also has a derivative reason to employ the means. This thesis is seldom contested since it seems quite intuitive. Failing to follow this requirement is a form of error, not only when judged from an external perspective, but even from the agent's own perspective: the agent cannot plead that he does not care since he already has a desire for the corresponding end.

On the other hand, contemporary Humeanism about practical reason includes the assertion that only our desires determine which initial reasons we have. So having a desire to swim at the beach provides the agent with a reason to do so, which in turn provides him with a reason to travel to the beach. On this view, whether the agent has this desire is not a matter of being rational or not. Rationality just requires that an agent who wants to swim at the beach should be motivated to travel there. This thesis has proved most controversial. Some have argued that desires do not provide reasons at all, or only in special cases. This position is often combined with an externalist view of rationality: that reasons are given not from the agent's psychological states but from objective facts about the world, for example, from what would be objectively best. This is reflected, for example, in the view that some desires are bad or irrational and can be criticized on these grounds. On this position, psychological states like desires may be motivational reasons, which move the agent, but not normative reasons, which determine what should be done. Others allow that desires provide reasons in the relevant sense but deny that this role is played only by desires. So there may be other psychological states or processes, like evaluative beliefs or deliberation, that also determine what we should do. This can be combined with the thesis that practical reason has something to say about which ends we should follow, for example, by having an impact either on these other states or on desires directly.

A common dispute between Humeans and Anti-Humeans in the field of practical reason concerns the status of morality. Anti-Humeans often assert that everyone has a reason to be moral. But this seems to be incompatible with the Humean position, according to which reasons depend on desires and not everyone has a desire to be moral. This poses the following threat: it may lead to cases where an agent simply justifies his immoral actions by pointing out that he had no desire to be moral. One way to respond to this problem is to draw a clear distinction between rationality and morality. If rationality is concerned with what should be done according to the agent's own perspective then it may well be rational to act immorally in cases when the agent lacks moral desires. Such actions are then rationally justified but immoral nonetheless. But it is a contested issue whether there really is such a gap between rationality and morality.

Metaethics

Central to Hume's position in metaethics is the is-ought distinction. It is guided by the idea that there is an important difference between is-statements, which concern facts about the natural world, and ought-statements, which are moral or evaluative claims about what should be done or what has value. The key aspect of this difference is that is-statements do not imply ought-statements. This is important, according to Hume, because this type of mistaken inference has been a frequent source of error in the history of philosophy. Based on this distinction, interpreters have often attributed various related philosophical theses to Hume in relation to contemporary debates in metaethics. One of these theses concerns the dispute between cognitivism and non-cognitivism. Cognitivists assert that ought-statements are truth-apt, i.e. are either true or false. They resemble is-statements in this sense, which is rejected by non-cognitivists. Some non-cognitivists deny that ought-statements have meaning at all. But the more common approach is to account for their meaning in other ways. Prescriptivists treat ought-statements as prescriptions or commands, which are meaningful without having a truth-value. Emotivists, on the other hand, hold that ought-statements merely express the speaker's emotional attitudes in the form of approval or disapproval. The debate between cognitivism and non-cognitivism concerns the semantic level about the meaning and truth-value of statements. It is reflected on the metaphysical level as the dispute about whether normative facts about what should be the case are part of reality, as realists claim, or not, as anti-realists contend. Based on Hume's denial that ought-statements are about facts, he is usually interpreted as an anti-realist. But interpreters of Hume have raised various doubts both for labeling him as an anti-realist and as a non-cognitivist.

Bundle theory of the self

In philosophy of mind, Hume is well known for his development of the bundle theory of the self. In his analyses, he uses the terms "self", "mind" and "person" interchangeably. He denies the traditional conception, usually associated with René Descartes, that the mind is constituted by a substance or an immaterial soul that acts as the bearer of all its mental states. The key to Hume's critique of this conception comes from his empirical outlook: that such a substance is never given as part of our experience. Instead, introspection only shows a manifold of mental states, referred to by Hume as "perceptions". For Hume, this epistemic finding implies a semantic conclusion: that the words "mind" or "self" cannot mean substance of mental states but must mean bundle of perceptions. This is the case because, according to Hume, words are associated with ideas and ideas are based on impressions. So without impressions of a mental substance, we lack the corresponding idea. Hume's theory is often interpreted as involving an ontological claim about what selves actually are, which goes beyond the semantic claim about what the word "self" means but. But others contend that this constitutes a misinterpretation of Hume since he restricts his claims to the epistemic and semantic level.

One problem for the bundle theory of the self is how to account for the unity of the self. This is usually understood in terms of diachronic unity, i.e. how the mind is unified with itself at different times or how it persists through time. But it can also be understood in terms of synchronic unity, i.e. how at one specific time, there is unity among the different mental states had by the same subject. A substance, unlike a simple collection, can explain either type of unity. This is why bundles are not equated with mere collections, the difference being that the bundled elements are linked to each other by a relation often referred to as "compresence", "co-personality" or "co-consciousness". Hume tried to understand this relation in terms of resemblance and causality. On this account, two perceptions belong to the same mind if they resemble each other and/or stand in the right causal relations to each other. Hume's particular version of this approach is usually rejected, but there are various other proposals on how to solve this problem compatible with the bundle theory. They include accounting for the unity in terms of psychological continuity or seeing it as a primitive aspect of the compresence-relation.

Hyperglycemia

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https://en.wikipedia.org/wiki/Hyperglycemia 

Hyperglycemia
Other names	High blood sugar, hyperglycaemia, hyperglycæmia
White hexagons in the image represent glucose molecules, which are increased in the lower image.
Specialty	Endocrinology

Hyperglycemia is a condition in which an excessive amount of glucose circulates in the blood plasma. This is generally a blood sugar level higher than 11.1 mmol/l (200 mg/dL), but symptoms may not start to become noticeable until even higher values such as 13.9–16.7 mmol/l (~250–300 mg/dL). A subject with a consistent range between ~5.6 and ~7 mmol/l (100–126 mg/dL) (American Diabetes Association guidelines) is considered slightly hyperglycemic, and above 7 mmol/l (126 mg/dL) is generally held to have diabetes. For diabetics, glucose levels that are considered to be too hyperglycemic can vary from person to person, mainly due to the person's renal threshold of glucose and overall glucose tolerance. On average, however, chronic levels above 10–12 mmol/L (180–216 mg/dL) can produce noticeable organ damage over time.

Signs and symptoms

The degree of hyperglycemia can change over time depending on the metabolic cause, for example, impaired glucose tolerance or fasting glucose, and it can depend on treatment. Temporary hyperglycemia is often benign and asymptomatic. Blood glucose levels can rise well above normal and cause pathological and functional changes for significant periods without producing any permanent effects or symptoms. During this asymptomatic period, an abnormality in carbohydrate metabolism can occur which can be tested by measuring plasma glucose. Chronic hyperglycemia at above normal levels can produce a very wide variety of serious complications over a period of years, including kidney damage, neurological damage, cardiovascular damage, damage to the retina or damage to feet and legs. Diabetic neuropathy may be a result of long-term hyperglycemia. Impairment of growth and susceptibility to certain infections can occur as a result of chronic hyperglycemia.

Acute hyperglycemia involving glucose levels that are extremely high is a medical emergency and can rapidly produce serious complications (such as fluid loss through osmotic diuresis). It is most often seen in persons who have uncontrolled insulin-dependent diabetes.

The following symptoms may be associated with acute or chronic hyperglycemia, with the first three composing the classic hyperglycemic triad:

• Polyphagia – frequent hunger, especially pronounced hunger
• Polydipsia – frequent thirst, especially excessive thirst
• Polyuria – increased volume of urination (not an increased frequency, although it is a common consequence)
• Blurred vision
• Fatigue
• Restlessness
• Weight loss or weight gain
• Poor wound healing (cuts, scrapes, etc.)
• Dry mouth
• Dry or itchy skin
• Tingling in feet or heels
• Erectile dysfunction
• Recurrent infections, external ear infections (swimmer's ear)
• Delayed gastric emptying
• Cardiac arrhythmia
• Stupor
• Coma
• Seizures
• Abnormal movements: chorea, choreoathetosis, ballism, dystonia, opsoclonus-myoclonus, parkinsonism, hemifacial spasm, and Holmes tremor

Frequent hunger without other symptoms can also indicate that blood sugar levels are too low. This may occur when people who have diabetes take too much oral hypoglycemic medication or insulin for the amount of food they eat. The resulting drop in blood sugar level to below the normal range prompts a hunger response.

Polydipsia and polyuria occur when blood glucose levels rise high enough to result in excretion of excess glucose via the kidneys, which leads to the presence of glucose in the urine. This produces an osmotic diuresis.

Signs and symptoms of diabetic ketoacidosis may include:

• Ketoacidosis
• Kussmaul hyperventilation (deep, rapid breathing)
• Confusion or a decreased level of consciousness
• Dehydration due to glycosuria and osmotic diuresis
• Increased thirst
• 'Fruity' smelling breath odor
• Nausea and vomiting
• Abdominal pain
• Impairment of cognitive function, along with increased sadness and anxiety
• Weight loss

Hyperglycemia causes a decrease in cognitive performance, specifically in processing speed, executive function, and performance. Decreased cognitive performance may cause forgetfulness and concentration loss.

Complications

In untreated hyperglycemia, a condition called ketoacidosis may develop because decreased insulin levels increase the activity of hormone sensitive lipase. The degradation of triacylglycerides by hormone-sensitive lipase produces free fatty acids that are eventually converted to acetyl-coA by beta-oxidation.

Ketoacidosis is a life-threatening condition which requires immediate treatment. Symptoms include: shortness of breath, breath that smells fruity (such as pear drops), nausea and vomiting, and very dry mouth. Chronic hyperglycemia (high blood sugar) injures the heart in patients without a history of heart disease or diabetes and is strongly associated with heart attacks and death in subjects with no coronary heart disease or history of heart failure.

Also, a life-threatening consequence of hyperglycemia is nonketotic hyperosmolar syndrome.

Perioperative hyperglycemia has been associated with immunosuppression, increased infections, osmotic diuresis, delayed wound healing, delayed gastric emptying, sympatho-adrenergic stimulation, and increased mortality.  In addition, it reduces skin graft success, exacerbates brain, spinal cord, and renal damage by ischemia, worsens neurologic outcomes in traumatic head injuries, and is associated with postoperative cognitive dysfunction following CABG.

Causes

Hyperglycemia may be caused by: diabetes, various (non-diabetic) endocrine disorders (insulin resistance and thyroid, adrenal, pancreatic, and pituitary disorders), sepsis and certain infections, intracranial diseases (e.g. encephalitis, brain tumors (especially if near the pituitary gland), brain haemorrhages, and meningitis) (frequently overlooked), convulsions, end-stage terminal disease, prolonged/major surgeries, excessive eating, severe stress, and physical trauma.

Endocrine

Chronic, persistent hyperglycaemia is most often a result of diabetes. Several hormones act to increase blood glucose levels and may thus cause hyperglycaemia when present in excess, including: cortisol, catecholamines, growth hormone, glucagon, and thyroid hormones. Hyperglycaemia may thus be seen in: Cushing's syndrome, pheochromocytoma, acromegaly, hyperglucagonemia, and hyperthyroidism.

Diabetes mellitus

Chronic hyperglycemia that persists even in fasting states is most commonly caused by diabetes mellitus. In fact, chronic hyperglycemia is the defining characteristic of the disease. Intermittent hyperglycemia may be present in prediabetic states. Acute episodes of hyperglycemia without an obvious cause may indicate developing diabetes or a predisposition to the disorder.

In diabetes mellitus, hyperglycemia is usually caused by low insulin levels (diabetes mellitus type 1) and/or by resistance to insulin at the cellular level (diabetes mellitus type 2), depending on the type and state of the disease. Low insulin levels and/or insulin resistance prevent the body from converting glucose into glycogen (a starch-like source of energy stored mostly in the liver), which in turn makes it difficult or impossible to remove excess glucose from the blood. With normal glucose levels, the total amount of glucose in the blood at any given moment is only enough to provide energy to the body for 20–30 minutes, and so glucose levels must be precisely maintained by the body's internal control mechanisms. When the mechanisms fail in a way that allows glucose to rise to abnormal levels, hyperglycemia is the result.

Ketoacidosis may be the first symptom of immune-mediated diabetes, particularly in children and adolescents. Also, patients with immune-mediated diabetes, can change from modest fasting hyperglycemia to severe hyperglycemia and even ketoacidosis as a result of stress or an infection.

Insulin resistance

Obesity has been contributing to increased insulin resistance due to the population's daily caloric intake rising. Insulin resistance increases hyperglycemia because the body becomes over saturated by glucose. Insulin resistance desensitizes insulin receptors, preventing insulin from lowering blood sugar levels.

The leading cause of hyperglycemia in type 2 diabetes is the failure of insulin to suppress glucose production by glycolysis and gluconeogenesis due to insulin resistance. Insulin normally inhibits glycogenolysis, but fails to do so in a condition of insulin resistance, resulting in increased glucose production. In the liver, FOXO6 normally promotes gluconeogenesis in the fasted state, but insulin blocks Fox06 upon feeding. In a condition of insulin resistance insulin fails to block FoxO6, resulting in continued gluconeogenesis even upon feeding.

Medications

Certain medications increase the risk of hyperglycemia, including: corticosteroids, octreotide, beta blockers, epinephrine, thiazide diuretics, statins, niacin, pentamidine, protease inhibitors, L-asparaginase, and antipsychotics. The acute administration of stimulants such as amphetamines typically produces hyperglycemia; chronic use, however, produces hypoglycemia.

Thiazides are used to treat type 2 diabetes but it also causes severe hyperglycemia.

Stress

A high proportion of patients suffering an acute stress such as stroke or myocardial infarction may develop hyperglycemia, even in the absence of a diagnosis of diabetes. (Or perhaps stroke or myocardial infarction was caused by hyperglycemia and undiagnosed diabetes.) Human and animal studies suggest that this is not benign, and that stress-induced hyperglycemia is associated with a high risk of mortality after both stroke and myocardial infarction. Somatostatinomas and aldosteronoma-induced hypokalemia can cause hyperglycemia but usually disappears after the removal of the tumour.

Stress causes hyperglycaemia via several mechanisms, including through metabolic and hormonal changes, and via increased proinflammatory cytokines that interrupt carbohydrate metabolism, leading to excessive glucose production and reduced uptake in tissues, can cause hyperglycemia.

Hormones such as the growth hormone, glucagon, cortisol and catecholamines, can cause hyperglycemia when they are present in the body in excess amounts.

Diagnosis

Monitoring

It is critical for patients who monitor glucose levels at home to be aware of which units of measurement their glucose meter uses. Glucose levels are measured in either:

1. Millimoles per liter (mmol/l) is the SI standard unit used in most countries around the world.
2. Milligrams per deciliter (mg/dl) is used in some countries such as the United States, Japan, France, Egypt and Colombia.

Scientific journals are moving towards using mmol/l; some journals now use mmol/l as the primary unit but quote mg/dl in parentheses.

Glucose levels vary before and after meals, and at various times of day; the definition of "normal" varies among medical professionals. In general, the normal range for most people (fasting adults) is about 4 to 6 mmol/l or 80 to 110 mg/dl. (where 4 mmol/l or 80 mg/dl is "optimal".) A subject with a consistent range above 7 mmol/l or 126 mg/dl is generally held to have hyperglycemia, whereas a consistent range below 4 mmol/l or 70 mg/dl is considered hypoglycemic. In fasting adults, blood plasma glucose should not exceed 7 mmol/l or 126 mg/dL. Sustained higher levels of blood sugar cause damage to the blood vessels and to the organs they supply, leading to the complications of diabetes.

Chronic hyperglycemia can be measured via the HbA1c test. The definition of acute hyperglycemia varies by study, with mmol/l levels from 8 to 15 (mg/dl levels from 144 to 270).

Defects in insulin secretion, insulin action, or both, results in hyperglycemia.

Chronic hyperglycemia can be measured by clinical urine tests which can detect sugar in the urine or microalbuminuria which could be a symptom of diabetes.

Group aerobic exercises

Treatment

Treatment of hyperglycemia requires elimination of the underlying cause, such as diabetes. Acute hyperglycemia can be treated by direct administration of insulin in most cases. Severe hyperglycemia can be treated with oral hypoglycemic therapy and lifestyle modification.

Replacing white bread with whole wheat may help reduce hyperglycemia

In diabetes mellitus (by far the most common cause of chronic hyperglycemia), treatment aims at maintaining blood glucose at a level as close to normal as possible, in order to avoid serious long-term complications. This is done by a combination of proper diet, regular exercise, and insulin or other medication such as metformin, etc.

Those with hyperglycaemia can be treated using sulphonylureas or metformin or both. These drugs help by improving glycaemic control. Dipeptidyl peptidase 4 inhibitor alone or in combination with basal insulin can be used as a treatment for hyperglycemia with patients still in hospital.

Increasing aerobic exercise to at least 30 minutes will make better use of glucose accumulated in the body since glucose is being used for energy by the muscle.

Calorie restriction would be one of the main lifestyle changes because it reduces over eating which contributes to hyperglycemia.

Diets higher in healthy unsaturated fats and whole wheat carbohydrates such as the Mediterranean diet can help reduce carbohydrate intake to better control hyperglycemia. Diets such as intermittent fasting and ketogenic diet help reduce calorie consumption which could significantly reduce hyperglycemia.

Carbohydrates are the main cause for hyperglycemia, non whole wheat items should be substituted for whole wheat items. Fruits are a part of a complete nutritious diet, but the intake of fruit should be limited due to its high sugar content.

Epidemiology

Environmental factors

Hyperglycemia is lower in higher income groups since there is access to better education and resources. Low-middle income groups are more likely to develop hyperglycemia due to lack of education and access to food options. Living in warmer climates can reduce hyperglycemia due to increased physical activity while people are less active in colder climates.

Population

Hyperglycemia is one of the main symptoms of diabetes and it has substantially affected the population making it an epidemic due to the population's increased calorie consumption. Healthcare providers are trying to work more closely with people allowing them more freedom with interventions that suit their lifestyle. As physical inactivity and calorie consumption increases it makes individuals more susceptible to developing hyperglycemia. Hyperglycemia is caused by type 1 diabetes and non-whites have a higher susceptibility for it.

Etymology

The origin of the term is Greek: prefix ὑπέρ- hyper- "over-", γλυκός glycos "sweet wine, must", αἷμα haima "blood", -ία, -εια -ia suffix for abstract nouns of feminine gender.

Electromagnetic field

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Covariant formulation

Scientists

An electromagnetic field (also EM field or EMF) is a classical (i.e. non-quantum) field produced by accelerating electric charges. It is the field described by classical electrodynamics and is the classical counterpart to the quantized electromagnetic field tensor in quantum electrodynamics. The electromagnetic field propagates at the speed of light (in fact, this field can be identified as light) and interacts with charges and currents. Its quantum counterpart is one of the four fundamental forces of nature (the others are gravitation, weak interaction and strong interaction.)

The field can be viewed as the combination of an electric field and a magnetic field. The electric field is produced by stationary charges, and the magnetic field by moving charges (currents); these two are often described as the sources of the field. The way in which charges and currents interact with the electromagnetic field is described by Maxwell's equations and the Lorentz force law. The force created by the electric field is much stronger than the force created by the magnetic field.

From a classical perspective in the history of electromagnetism, the electromagnetic field can be regarded as a smooth, continuous field, propagated in a wavelike manner. By contrast, from the perspective of quantum field theory, this field is seen as quantized; meaning that the free quantum field (i.e. non-interacting field) can be expressed as the Fourier sum of creation and annihilation operators in energy-momentum space while the effects of the interacting quantum field may be analyzed in perturbation theory via the S-matrix with the aid of a whole host of mathematical techniques such as the Dyson series, Wick's theorem, correlation functions, time-evolution operators, Feynman diagrams etc. Note that the quantized field is still spatially continuous; its energy states however are discrete (the field's energy states must not be confused with its energy values, which are continuous; the quantum field's creation operators create multiple discrete states of energy called photons.)

A sinusoidal electromagnetic wave propagating along the positive z-axis, showing the electric field (blue) and magnetic field (red) vectors.

Structure

The electromagnetic field may be viewed in two distinct ways: a continuous structure or a discrete structure.

Continuous structure

Classically, electric and magnetic fields are thought of as being produced by smooth motions of charged objects. For example, oscillating charges produce variations in electric and magnetic fields that may be viewed in a 'smooth', continuous, wavelike fashion. In this case, energy is viewed as being transferred continuously through the electromagnetic field between any two locations. For instance, the metal atoms in a radio transmitter appear to transfer energy continuously. This view is useful to a certain extent (radiation of low frequency), however, problems are found at high frequencies (see ultraviolet catastrophe).

Discrete structure

The electromagnetic field may be thought of in a more 'coarse' way. Experiments reveal that in some circumstances electromagnetic energy transfer is better described as being carried in the form of packets called quanta with a fixed frequency. Planck's relation links the photon energy E of a photon to its frequency f through the equation:

${\displaystyle E=\,hf}$

where h is Planck's constant, and f is the frequency of the photon. Although modern quantum optics tells us that there also is a semi-classical explanation of the photoelectric effect—the emission of electrons from metallic surfaces subjected to electromagnetic radiation—the photon was historically (although not strictly necessarily) used to explain certain observations. It is found that increasing the intensity of the incident radiation (so long as one remains in the linear regime) increases only the number of electrons ejected, and has almost no effect on the energy distribution of their ejection. Only the frequency of the radiation is relevant to the energy of the ejected electrons.

This quantum picture of the electromagnetic field (which treats it as analogous to harmonic oscillators) has proven very successful, giving rise to quantum electrodynamics, a quantum field theory describing the interaction of electromagnetic radiation with charged matter. It also gives rise to quantum optics, which is different from quantum electrodynamics in that the matter itself is modelled using quantum mechanics rather than quantum field theory.

Dynamics

In the past, electrically charged objects were thought to produce two different, unrelated types of field associated with their charge property. An electric field is produced when the charge is stationary with respect to an observer measuring the properties of the charge, and a magnetic field as well as an electric field is produced when the charge moves, creating an electric current with respect to this observer. Over time, it was realized that the electric and magnetic fields are better thought of as two parts of a greater whole—the electromagnetic field. Until 1820, when the Danish physicist H. C. Ørsted showed the effect of electric current on a compass needle, electricity and magnetism had been viewed as unrelated phenomena. In 1831, Michael Faraday made the seminal observation that time-varying magnetic fields could induce electric currents and then, in 1864, James Clerk Maxwell published his famous paper "A Dynamical Theory of the Electromagnetic Field".

Once this electromagnetic field has been produced from a given charge distribution, other charged or magnetised objects in this field may experience a force. If these other charges and currents are comparable in size to the sources producing the above electromagnetic field, then a new net electromagnetic field will be produced. Thus, the electromagnetic field may be viewed as a dynamic entity that causes other charges and currents to move, and which is also affected by them. These interactions are described by Maxwell's equations and the Lorentz force law. This discussion ignores the radiation reaction force. Note, however, this is not a statement of the ontic status of the electromagnetic field as a physical entity, but merely a methodological treatment; Indeed, the Standard Model predicates that the electromagnetic field is an emergent phenomenon of the fundamental particles, including photons.

Feedback loop

The behavior of the electromagnetic field can be divided into four different parts of a loop:

• the electric and magnetic fields are generated by moving electric charges,
• the electric and magnetic fields interact with each other,
• the electric and magnetic fields produce forces on electric charges,
• the electric charges move in space.

A common misunderstanding is that (a) the quanta of the fields act in the same manner as (b) the charged particles, such as electrons, that generate the fields. In our everyday world, electrons travel slowly through conductors with a drift velocity of a fraction of a centimeter per second and through a vacuum tube at speeds of around 1 thousand km/s, but fields propagate at the speed of light, approximately 300 thousand kilometers (or 186 thousand miles) a second. The speed ratio between charged particles in a conductor and field quanta is on the order of one to a million. Maxwell's equations relate (a) the presence and movement of charged particles with (b) the generation of fields. Those fields can then affect the force on, and can then move other slowly moving charged particles. Charged particles can move at relativistic speeds nearing field propagation speeds, but, as Albert Einstein showed, this requires enormous field energies, which are not present in our everyday experiences with electricity, magnetism, matter, and time and space.

The feedback loop can be summarized in a list, including phenomena belonging to each part of the loop:

• charged particles generate electric and magnetic fields
• the fields interact with each other
  • changing electric field acts like a current, generating 'vortex' of magnetic field
  • Faraday induction: changing magnetic field induces (negative) vortex of electric field
  • Lenz's law: negative feedback loop between electric and magnetic fields
• fields act upon particles
  • Lorentz force: force due to electromagnetic field
    • electric force: same direction as electric field
    • magnetic force: perpendicular both to magnetic field and to velocity of charge
• charged particles move
  • current is movement of particles
• charged particles generate more electric and magnetic fields; cycle repeats

Mathematical description

Main article: Mathematical descriptions of the electromagnetic field

There are different mathematical ways of representing the electromagnetic field. The first one views the electric and magnetic fields as three-dimensional vector fields. These vector fields each have a value defined at every point of space and time and are thus often regarded as functions of the space and time coordinates. As such, they are often written as E(x, y, z, t) (electric field) and B(x, y, z, t) (magnetic field).

If only the electric field (E) is non-zero, and is constant in time, the field is said to be an electrostatic field. Similarly, if only the magnetic field (B) is non-zero and is constant in time, the field is said to be a magnetostatic field. However, if either the electric or magnetic field has a time-dependence, then both fields must be considered together as a coupled electromagnetic field using Maxwell's equations.

With the advent of special relativity, physical laws became susceptible to the formalism of tensors. Maxwell's equations can be written in tensor form, generally viewed by physicists as a more elegant means of expressing physical laws.

The behavior of electric and magnetic fields, whether in cases of electrostatics, magnetostatics, or electrodynamics (electromagnetic fields), is governed by Maxwell's equations. In the vector field formalism, these are:

Gauss's law

${\displaystyle \nabla \cdot \mathbf {E} ={\frac {\rho }{\varepsilon _{0}}}}$

Gauss's law for magnetism

${\displaystyle \nabla \cdot \mathbf {B} =0}$

Faraday's law

${\displaystyle \nabla \times \mathbf {E} =-{\frac {\partial \mathbf {B} }{\partial t}}}$

Maxwell–Ampère law

${\displaystyle \nabla \times \mathbf {B} =\mu _{0}\mathbf {J} +\mu _{0}\varepsilon _{0}{\frac {\partial \mathbf {E} }{\partial t}}}$

where ${\displaystyle \rho }$ is the charge density, which can (and often does) depend on time and position, ${\displaystyle \varepsilon _{0}}$ is the permittivity of free space, ${\displaystyle \mu _{0}}$ is the permeability of free space, and J is the current density vector, also a function of time and position. The units used above are the standard SI units. Inside a linear material, Maxwell's equations change by switching the permeability and permittivity of free space with the permeability and permittivity of the linear material in question. Inside other materials which possess more complex responses to electromagnetic fields, these terms are often represented by complex numbers, or tensors.

The Lorentz force law governs the interaction of the electromagnetic field with charged matter.

When a field travels across to different media, the properties of the field change according to the various boundary conditions. These equations are derived from Maxwell's equations. The tangential components of the electric and magnetic fields as they relate on the boundary of two media are as follows:

$${\displaystyle \mathbf {E} _{1}=\mathbf {E} _{2}}$$

$${\displaystyle \mathbf {H} _{1}=\mathbf {H} _{2}}$$

(current-free)

$${\displaystyle \mathbf {D} _{1}=\mathbf {D} _{2}}$$

(charge-free)

$${\displaystyle \mathbf {B} _{1}=\mathbf {B} _{2}}$$

The angle of refraction of an electric field between media is related to the permittivity ${\displaystyle (\varepsilon )}$ of each medium:

$${\displaystyle {\frac {\tan \theta _{1}}{\tan \theta _{2}}}={\frac {\varepsilon _{r2}}{\varepsilon _{r1}}}}$$

The angle of refraction of a magnetic field between media is related to the permeability ${\displaystyle (\mu )}$ of each medium:

$${\displaystyle {\frac {\tan \theta _{1}}{\tan \theta _{2}}}={\frac {\mu _{r2}}{\mu _{r1}}}}$$

Properties of the field

Reciprocal behavior of electric and magnetic fields

The two Maxwell equations, Faraday's Law and the Ampère-Maxwell Law, illustrate a very practical feature of the electromagnetic field. Faraday's Law may be stated roughly as 'a changing magnetic field creates an electric field'. This is the principle behind the electric generator.

Ampere's Law roughly states that 'a changing electric field creates a magnetic field'. Thus, this law can be applied to generate a magnetic field and run an electric motor.

Behavior of the fields in the absence of charges or currents

Maxwell's equations take the form of an electromagnetic wave in a volume of space not containing charges or currents (free space) – that is, where ${\displaystyle \rho }$ and J are zero. Under these conditions, the electric and magnetic fields satisfy the electromagnetic wave equation:

${\displaystyle \left(\nabla ^{2}-{1 \over {c}^{2}}{\partial ^{2} \over \partial t^{2}}\right)\mathbf {E} \ \ =\ \ 0}$

${\displaystyle \left(\nabla ^{2}-{1 \over {c}^{2}}{\partial ^{2} \over \partial t^{2}}\right)\mathbf {B} \ \ =\ \ 0}$

James Clerk Maxwell was the first to obtain this relationship by his completion of Maxwell's equations with the addition of a displacement current term to Ampere's circuital law.

Relation to and comparison with other physical fields

Main article: Fundamental forces

Being one of the four fundamental forces of nature, it is useful to compare the electromagnetic field with the gravitational, strong and weak fields. The word 'force' is sometimes replaced by 'interaction' because modern particle physics models electromagnetism as an exchange of particles known as gauge bosons.

Electromagnetic and gravitational fields

Sources of electromagnetic fields consist of two types of charge – positive and negative. This contrasts with the sources of the gravitational field, which are masses. Masses are sometimes described as gravitational charges, the important feature of them being that there are only positive masses and no negative masses. Further, gravity differs from electromagnetism in that positive masses attract other positive masses whereas same charges in electromagnetism repel each other.

The relative strengths and ranges of the four interactions and other information are tabulated below:

Theory	Interaction	mediator	Relative Magnitude	Behavior	Range
Chromodynamics	Strong interaction	gluon	1038	1	10−15 m
Electrodynamics	Electromagnetic interaction	photon	1036	1/r2	infinite
Flavordynamics	Weak interaction	W and Z bosons	1025	1/r5 to 1/r7	10−16 m
Geometrodynamics	Gravitation	graviton (hypothesised)	100	1/r2	infinite

Applications

Static E and M fields and static EM fields

Main articles: electrostatics, magnetostatics, and magnetism

When an EM field (see electromagnetic tensor) is not varying in time, it may be seen as a purely electrical field or a purely magnetic field, or a mixture of both. However the general case of a static EM field with both electric and magnetic components present, is the case that appears to most observers. Observers who see only an electric or magnetic field component of a static EM field, have the other (electric or magnetic) component suppressed, due to the special case of the immobile state of the charges that produce the EM field in that case. In such cases the other component becomes manifest in other observer frames.

A consequence of this, is that any case that seems to consist of a "pure" static electric or magnetic field, can be converted to an EM field, with both E and M components present, by simply moving the observer into a frame of reference which is moving with regard to the frame in which only the "pure" electric or magnetic field appears. That is, a pure static electric field will show the familiar magnetic field associated with a current, in any frame of reference where the charge moves. Likewise, any new motion of a charge in a region that seemed previously to contain only a magnetic field, will show that the space now contains an electric field as well, which will be found to produce an additional Lorentz force upon the moving charge.

Thus, electrostatics, as well as magnetism and magnetostatics, are now seen as studies of the static EM field when a particular frame has been selected to suppress the other type of field, and since an EM field with both electric and magnetic will appear in any other frame, these "simpler" effects are merely the observer's. The "applications" of all such non-time varying (static) fields are discussed in the main articles linked in this section.

Time-varying EM fields in Maxwell’s equations

Main articles: near and far field, near field optics, virtual particle, dielectric heating, and Electromagnetic induction

An EM field that varies in time has two "causes" in Maxwell's equations. One is charges and currents (so-called "sources"), and the other cause for an E or M field is a change in the other type of field (this last cause also appears in "free space" very far from currents and charges).

An electromagnetic field very far from currents and charges (sources) is called electromagnetic radiation (EMR) since it radiates from the charges and currents in the source, and has no "feedback" effect on them, and is also not affected directly by them in the present time (rather, it is indirectly produced by a sequences of changes in fields radiating out from them in the past). EMR consists of the radiations in the electromagnetic spectrum, including radio waves, microwave, infrared, visible light, ultraviolet light, X-rays, and gamma rays. The many commercial applications of these radiations are discussed in the named and linked articles.

A notable application of visible light is that this type of energy from the Sun powers all life on Earth that either makes or uses oxygen.

A changing electromagnetic field which is physically close to currents and charges (see near and far field for a definition of "close") will have a dipole characteristic that is dominated by either a changing electric dipole, or a changing magnetic dipole. This type of dipole field near sources is called an electromagnetic near-field.

Changing electric dipole fields, as such, are used commercially as near-fields mainly as a source of dielectric heating. Otherwise, they appear parasitically around conductors which absorb EMR, and around antennas which have the purpose of generating EMR at greater distances.

Changing magnetic dipole fields (i.e., magnetic near-fields) are used commercially for many types of magnetic induction devices. These include motors and electrical transformers at low frequencies, and devices such as metal detectors and MRI scanner coils at higher frequencies. Sometimes these high-frequency magnetic fields change at radio frequencies without being far-field waves and thus radio waves; see RFID tags. See also near-field communication. Further uses of near-field EM effects commercially may be found in the article on virtual photons, since at the quantum level, these fields are represented by these particles. Far-field effects (EMR) in the quantum picture of radiation are represented by ordinary photons.

Other

• Electromagnetic field can be used to record data on static electricity.
• Old televisions can be traced with electromagnetic fields.

Health and safety

The potential effects of electromagnetic fields on human health vary widely depending on the frequency and intensity of the fields.

The potential health effects of the very low frequency EMFs surrounding power lines and electrical devices are the subject of on-going research and a significant amount of public debate. The US National Institute for Occupational Safety and Health (NIOSH) and other US government agencies do not consider EMFs a proven health hazard. NIOSH has issued some cautionary advisories but stresses that the data are currently too limited to draw good conclusions. In 2011, The WHO/International Agency for Research on Cancer (IARC) classified radiofrequency electromagnetic fields as possibly carcinogenic to humans (Group 2B), based on an increased risk for glioma, a malignant type of brain cancer, associated with wireless phone use.

Employees working at electrical equipment and installations can always be assumed to be exposed to electromagnetic fields. The exposure of office workers to fields generated by computers, monitors, etc. is negligible owing to the low field strengths. However, industrial installations for induction hardening and melting or on welding equipment may produce considerably higher field strengths and require further examination. If the exposure cannot be determined upon manufacturers' information, comparisons with similar systems or analytical calculations, measurements have to be accomplished. The results of the evaluation help to assess possible hazards to the safety and health of workers and to define protective measures. Since electromagnetic fields may influence passive or active implants of workers, it is essential to consider the exposure at their workplaces separately in the risk assessment.

On the other hand, radiation from other parts of the electromagnetic spectrum, such as ultraviolet light and gamma rays, are known to cause significant harm in some circumstances. For more information on the health effects due to specific electromagnetic phenomena and parts of the electromagnetic spectrum, see the following articles:

• Static electric fields: see Electric shock
• Static magnetic fields: see MRI#Safety
• Extremely low frequency (ELF): see Power lines#Health concerns
• Radio frequency (RF): see Electromagnetic radiation and health
• Mobile telephony: see Mobile phone radiation and health
• Light: see Laser safety
• Ultraviolet (UV): see Sunburn, Photokeratitis
• Gamma rays: see Gamma ray