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Tuesday, November 8, 2022

Hydraulic analogy

From Wikipedia, the free encyclopedia
 
Analogy between a hydraulic circuit (left) and an electronic circuit (right).

The electronic–hydraulic analogy (derisively referred to as the drain-pipe theory by Oliver Lodge) is the most widely used analogy for "electron fluid" in a metal conductor. Since electric current is invisible and the processes in play in electronics are often difficult to demonstrate, the various electronic components are represented by hydraulic equivalents. Electricity (as well as heat) was originally understood to be a kind of fluid, and the names of certain electric quantities (such as current) are derived from hydraulic equivalents. As with all analogies, it demands an intuitive and competent understanding of the baseline paradigms (electronics and hydraulics).

Paradigms

There is no unique paradigm for establishing this analogy. Two paradigms can be used to introduce the concept to students using pressure induced by gravity or by pumps.

In the version with pressure induced by gravity, large tanks of water are held up high, or are filled to differing water levels, and the potential energy of the water head is the pressure source. This is reminiscent of electrical diagrams with an up arrow pointing to +V, grounded pins that otherwise are not shown connecting to anything, and so on. This has the advantage of associating electric potential with gravitational potential.

A second paradigm is a completely enclosed version with pumps providing pressure only and no gravity. This is reminiscent of a circuit diagram with a voltage source shown and the wires actually completing a circuit. This paradigm is further discussed below.

Other paradigms highlight the similarities between equations governing the flow of fluid and the flow of charge. Flow and pressure variables can be calculated in both steady and transient fluid flow situations with the use of the hydraulic ohm analogy. Hydraulic ohms are the units of hydraulic impedance, which is defined as the ratio of pressure to volume flow rate. The pressure and volume flow variables are treated as phasors in this definition, so possess a phase as well as magnitude.

A slightly different paradigm is used in acoustics, where acoustic impedance is defined as a relationship between acoustic pressure and acoustic particle velocity. In this paradigm, a large cavity with a hole is analogous to a capacitor that stores compressional energy when the time-dependent pressure deviates from atmospheric pressure. A hole (or long tube) is analogous to an inductor that stores kinetic energy associated with the flow of air.

Hydraulic analogy with horizontal water flow

Voltage, current, and charge

In general, electric potential is equivalent to hydraulic head. This model assumes that the water is flowing horizontally, so that the force of gravity can be ignored. In this case, electric potential is equivalent to pressure. The voltage (or voltage drop or potential difference) is a difference in pressure between two points. Electric potential and voltage are usually measured in volts.

Electric current is equivalent to a hydraulic volume flow rate; that is, the volumetric quantity of flowing water over time. Usually measured in amperes.

Electric charge is equivalent to a quantity of water.

Basic circuit elements

A relatively wide hose completely filled with water is equivalent to a conducting wire. A rigidly mounted pipe is equivalent to a trace on a circuit board. When comparing to a trace or wire, the hose or pipe should be thought of as having semi-permanent caps on the ends. Connecting one end of a wire to a circuit is equivalent to un-capping one end of the hose and attaching it to another. With few exceptions (such as a high-voltage power source), a wire with only one end attached to a circuit will do nothing; the hose remains capped on the free end, and thus adds nothing to the circuit.

A resistor is equivalent to a constriction in the bore of a pipe which requires more pressure to pass the same amount of water. All pipes have some resistance to flow, just as all wires and traces have some resistance to current.

A node (or junction) in Kirchhoff's junction rule is equivalent to a pipe tee. The net flow of water into a piping tee (filled with water) must equal the net flow out.

A capacitor is equivalent to a tank with one connection at each end and a rubber sheet dividing the tank in two lengthwise (a hydraulic accumulator). When water is forced into one pipe, equal water is simultaneously forced out of the other pipe, yet no water can penetrate the rubber diaphragm. Energy is stored by the stretching of the rubber. As more current flows "through" the capacitor, the back-pressure (voltage) becomes greater, thus current "leads" voltage in a capacitor. As the back-pressure from the stretched rubber approaches the applied pressure, the current becomes less and less. Thus capacitors "filter out" constant pressure differences and slowly varying, low-frequency pressure differences, while allowing rapid changes in pressure to pass through.

An inductor is equivalent to a heavy paddle wheel placed in the current. The mass of the wheel and the size of the blades restrict the water's ability to rapidly change its rate of flow (current) through the wheel due to the effects of inertia, but, given time, a constant flowing stream will pass mostly unimpeded through the wheel, as it turns at the same speed as the water flow. The mass and surface area of the wheel and its blades are analogous to inductance, and friction between its axle and the axle bearings corresponds to the resistance that accompanies any non-superconducting inductor.

An alternative inductor model is simply a long pipe, perhaps coiled into a spiral for convenience. This fluid-inertia device is used in real life as an essential component of a hydraulic ram. The inertia of the water flowing through the pipe produces the inductance effect; inductors "filter out" rapid changes in flow, while allowing slow variations in current to be passed through. The drag imposed by the walls of the pipe is somewhat analogous to parasitic resistance. In either model, the pressure difference (voltage) across the device must be present before the current will start moving, thus in inductors, voltage "leads" current. As the current increases, approaching the limits imposed by its own internal friction and of the current that the rest of the circuit can provide, the pressure drop across the device becomes lower and lower.

An ideal voltage source (ideal battery) or ideal current source is a dynamic pump with feedback control. A pressure meter on both sides shows that regardless of the current being produced, this kind of pump produces constant pressure difference. If one terminal is kept fixed at ground, another analogy is a large body of water at a high elevation, sufficiently large that the drawn water does not affect the water level. To create the analog of an ideal current source, use a positive displacement pump: A current meter (little paddle wheel) shows that when this kind of pump is driven at a constant speed, it maintains a constant speed of the little paddle wheel.

Other circuit elements

A diode is equivalent to a one-way check valve with a slightly leaky valve seat. As with a diode, a small pressure difference is needed before the valve opens. And like a diode, too much reverse bias can damage or destroy the valve assembly.

A transistor is a valve in which a diaphragm, controlled by a low-current signal (either constant current for a BJT or constant pressure for a FET), moves a plunger which affects the current through another section of pipe.

CMOS is a combination of two MOSFET transistors. As the input pressure changes, the pistons allow the output to connect to either zero or positive pressure.

A memristor is a needle valve operated by a flow meter. As water flows through in the forward direction, the needle valve restricts flow more; as water flows the other direction, the needle valve opens further, providing less resistance.

Practical application

On the basis of this analogy Johan van Veen developed around 1937 a method to compute tidal currents with an electric analogue. After the North Sea flood of 1953 in The Netherlands he elaborated this idea, which eventually lead to the analog computer ‘’Deltar’’, which was used to make the hydraulic computations for the closures in the framework of the Delta Works.

Principal equivalents

EM wave speed (velocity of propagation) is equivalent to the speed of sound in water. When a light switch is flipped, the electric wave travels very quickly through the wires.

Charge flow speed (drift velocity) is equivalent to the particle speed of water. The moving charges themselves move rather slowly.

DC is equivalent to the a constant flow of water in a circuit of pipes.

Low frequency AC is equivalent to water oscillating back and forth in a pipe

Higher-frequency AC and transmission lines is somewhat equivalent to sound being transmitted through the water pipes, though this does not properly mirror the cyclical reversal of alternating electric current. As described, the fluid flow conveys pressure fluctuations, but fluids do not reverse at high rates in hydraulic systems, which the above "low frequency" entry does accurately describe. A better concept (if sound waves are to be the phenomenon) is that of direct current with high-frequency "ripple" superimposed.

Inductive spark used in induction coils is similar to water hammer, caused by the inertia of water

Equation examples

Some examples of analogous electrical and hydraulic equations:

type hydraulic electric thermal mechanical
quantity volume [m3] charge [C] heat [J] momentum [Ns]
quantity flux Volumetric flow rate [m3/s] current [A=C/s] heat transfer rate [J/s] velocity [m/s=J/Ns]
flux density velocity [m/s] current density [C/(m2·s) = A/m²] heat flux [W/m2] stress [N/m2 = Pa]
potential pressure [Pa=J/m3=N/m2] potential [V=J/C=W/A] temperature [K] force [N]
linear model Poiseuille's law Ohm's law Fourier's law dashpot

If the differential equations have the same form, the response will be similar.

Limits to the analogy

If taken too far, the water analogy can create misconceptions. For it to be useful, one must remain aware of the regions where electricity and water behave very differently.

Fields (Maxwell equations, inductance): Electrons can push or pull other distant electrons via their fields, while water molecules experience forces only from direct contact with other molecules. For this reason, waves in water travel at the speed of sound, but waves in a sea of charge will travel much faster as the forces from one electron are applied to many distant electrons and not to only the neighbors in direct contact. In a hydraulic transmission line, the energy flows as mechanical waves through the water, but in an electric transmission line the energy flows as fields in the space surrounding the wires, and does not flow inside the metal. Also, an accelerating electron will drag its neighbors along while attracting them, both because of magnetic forces.

Charge: Unlike water, movable charge carriers can be positive or negative, and conductors can exhibit an overall positive or negative net charge. The mobile carriers in electric currents are usually electrons, but sometimes they are charged positively, such as the positive ions in an electrolyte, the H+ ions in proton conductors or holes in p-type semiconductors and some (very rare) conductors.

Leaking pipes: The electric charge of an electrical circuit and its elements is usually almost equal to zero, hence it is (almost) constant. This is formalized in Kirchhoff's current law, which does not have an analogy to hydraulic systems, where the amount of the liquid is not usually constant. Even with incompressible liquid the system may contain such elements as pistons and open pools, so the volume of liquid contained in a part of the system can change. For this reason, continuing electric currents require closed loops rather than hydraulics' open source/sink resembling spigots and buckets.

Fluid velocity and resistance of metals: As with water hoses, the carrier drift velocity in conductors is directly proportional to current. However, water only experiences drag via the pipes' inner surface, while charges are slowed at all points within a metal, as with water forced through a filter. Also, typical velocity of charge carriers within a conductor is less than centimeters per minute, and the "electrical friction" is extremely high. If charges ever flowed as fast as water can flow in pipes, the electric current would be immense, and the conductors would become incandescently hot and perhaps vaporize. To model the resistance and the charge-velocity of metals, perhaps a pipe packed with sponge, or a narrow straw filled with syrup, would be a better analogy than a large-diameter water pipe.

Quantum mechanics: Solid conductors and insulators contain charges at more than one discrete level of atomic orbit energy, while the water in one region of a pipe can only have a single value of pressure. For this reason there is no hydraulic explanation for such things as a battery's charge pumping ability, a diode's depletion layer and voltage drop, solar cell functions, Peltier effect, etc., however equivalent devices can be designed which exhibit similar responses, although some of the mechanisms would only serve to regulate the flow curves rather than to contribute to the component's primary function.

In order for the model to be useful, the reader or student must have a substantial understanding of the model (hydraulic) system's principles. It also requires that the principles can be transferred to the target (electrical) system. Hydraulic systems are deceptively simple: the phenomenon of pump cavitation is a known, complex problem that few people outside of the fluid power or irrigation industries would understand. For those who do, the hydraulic analogy is amusing, as no "cavitation" equivalent exists in electrical engineering. The hydraulic analogy can give a mistaken sense of understanding that will be exposed once a detailed description of electrical circuit theory is required.

One must also consider the difficulties in trying to make an analogy match reality completely. The above "electrical friction" example, where the hydraulic analog is a pipe filled with sponge material, illustrates the problem: the model must be increased in complexity beyond any realistic scenario.

Medicine in ancient Rome

From Wikipedia, the free encyclopedia
 
Ancient Roman coin depicting Vejovis, the Roman god of medicine throwing a thunderbolt

Medicine in ancient Rome was highly influenced by ancient Greek medicine, but also developed new practices through knowledge of the Hippocratic Corpus combined with use of the treatment of diet, regimen, along with surgical procedures. This was most notably seen through the works of two of the prominent Greek physicians, Dioscorides and Galen, who practiced medicine and recorded their discoveries. This is contrary to two other physicians like Soranus of Ephesus and Asclepiades of Bithynia, who practiced medicine both in outside territories and in ancient Roman territory, subsequently. Dioscorides was a Roman army physician, Soranus was a representative for the Methodic school of medicine, Galen performed public demonstrations, and Asclepiades was a leading Roman physician. These four physicians all had knowledge of medicine, ailments, and treatments that were healing, long lasting and influential to human history.

Ancient Roman medicine was divided into specializations such as ophthalmology and urology. To increase their knowledge of the human body, physicians used a variety of surgical procedures for dissection that were carried out using many different instruments including forceps, scalpels and catheters.

Introduction

The Roman Empire was a complex and vigorous combination of Greek and Roman cultural elements forged through centuries of contact. Later Latin authors, notably Cato and Pliny, believed in a specific traditional Roman type of healing based on herbs, chants, prayers and charms easily available to and by the head of household.

Greek medicine was introduced into Italy with the establishment and development of military and political contacts between the two regions. It was not until the introduction of the healing god Asclepius in 291 BC and the arrival of the Greek doctor Archagathus in 219 BC that foreign medicine was publicly accepted in Rome, mainly due to future overall adaptation to the Roman practices.

Setting aside some of the broader implications of the Greek influence on Roman society, the effect of ancient Greek medicine, ethnography, and meteorology was particularly pertinent to two fields: architecture and health care. This was particularly important from the perspective of the Roman army, in which there were many medical advances. A medical corpus was established, permanent physicians were appointed, the valetudinaria (military hospitals) were established, and in Caesar's time, the first traces of systematic care for the wounded appeared. The variety and nature of the surgical instruments discovered in Roman remains indicate a good knowledge of surgery.

Roman medicine

Roman medicine was highly influenced by the Greek medical tradition. Prior to the introduction of Greek medicine Roman medicine was a combination of religion and magic. The first Roman physicians were religious figures with no medical training or the head of the family. The first professional physicians were Greek physicians. Asclepiades of Bithynia arrived in 124 BC. He was a popular physician known for his kindness to his patients often prescribing wine, rest and a swinging couch. The incorporation of Greek medicine into Roman society allowed Rome to transform into a monumental city by 100 BC. Like Greek physicians, Roman physicians relied on naturalistic observations rather than on spiritual rituals; but that does not imply an absence of spiritual belief. Tragic famines and plagues were often attributed to divine punishment; and appeasement of the gods through rituals was believed to alleviate such events. Miasma was perceived to be the root cause of many diseases, whether caused by famine, wars, or plague. The concept of contagion was formulated, resulting in practices of quarantine and improved sanitation. The Romans established systems of public hygiene indicating there was an understanding that this was of importance to public health. This can be seen in their practices of burying the dead outside the city walls, their large supplies of water available through aqueducts, public bathing areas and public sewage systems. They also began draining swamps in close proximity to cities.

One of the first prominent doctors in Rome was Galen. He became an expert on the human anatomy by dissecting animals, including monkeys, in Greece. Due to his prominence and expertise in ancient Rome, Galen became Emperor Marcus Aurelius' personal physician.

Caduceus of Mercury; Stadtmuseum Rapperswil-Jona, Rapperswil, Switzerland

In 46 BC, Julius Caesar granted Roman citizenship to physicians when the Roman army had a need for trained surgeons. The Romans conquered the city of Alexandria in 30 BC, which was an important center for learning; its Great Library held countless volumes of ancient Greek medical information. The Romans adopted into their medical practices many of the practices and procedures they found in the Great Library. Augustus gave immunity to physicians from paying taxes and public duties in 10 AD. These incentives to physicians caused physicians to flood to Rome not all were educated physicians some were practicing without the proper education or training. Many of the those making false claims were claiming to be specialist. These incentives were eventually only offered to a certain number of physicians per region that worked for the public.

Greek symbols and gods greatly influenced ancient Roman medicine. The caduceus was originally associated with Hermes, the Greek god of commerce. He carried a staff wrapped with two snakes, known as the caduceus. This symbol later became associated with the Roman god Mercury. Later, in the 7th century, the caduceus became associated with health and medicine due to its association with the Azoth, the alchemical "universal solvent".

Opposition to Greek medicine in Rome / Pre-Physicians

Cato the Elder despised every aspect of Greek society the Romans decided to mimic including sculptures, literature and medicine. He regarded the welcome given in Rome to Greek medicine and physicians as a major threat. In Rome, before there were doctors, the paterfamilias (head of the family) was responsible for treating the sick. Cato the Elder himself examined those who lived near him, often prescribing cabbage as a treatment for many ailments ranging from constipation to deafness. He would issue precise instructions on how to prepare the cabbage for patients with specific ailments. He also used cabbage in liquid form. For example, a mixture of cabbage, water, and wine would be embedded in a deaf man's ear to allow his hearing to be restored. Cato would treat fractured or broken appendages with two ends of a cut reed that were bandaged around the injury.

Contributors

Many Greek doctors came to Rome. Many of them strongly believed in achieving the right balance of the four humors and restoring the natural heat of patients. Around 200 BC many wealthy families in Rome had personal Greek physicians. By around 50 BC, it was more common than not to have a Greek physician. Physicians were also more inclined to study anthropology, biology and physiology because of the great impact that philosophy had on them. The popular belief was that philosophy created interest in medicine as opposed to medicine creating an interest in philosophy.

Dioscorides

Illustration of Dioscorides

Pedanius Dioscorides (c. 40–90 AD), was a Greek botanist, pharmacologist and physician who practiced in Rome during the reign of Nero. Dioscorides studied botany and pharmacology in Tarsus. He became a well-known army surgeon. While traveling with the army, Dioscorides was able to experiment with the medical properties of many plants. Compared to his predecessors, his work was considered the largest and most thorough in regards to naming and writing about medicines, many of Dioscorides predecessors work was lost. Dioscorides wrote a 5-volume encyclopedia, De materia medica, which listed over 600 herbal cures, forming an influential and long-lasting pharmacopoeia. De materia medica was used extensively by doctors for the following 1500 years. Within his five books, Dioscorides mentions approximately 1,000 simple drugs. Also . . . contained in his books, Dioscorides refers to opium and mandragora as a sleeping potion that can be used as a natural surgical anesthetic.

Galen

A group of physicians in an image from the Vienna Dioscurides; Galen is depicted top center.

Galen of Pergamon (129 – c. AD 216) was a prominent Greek physician, whose theories dominated Western medical science for well over a millennium. By the age of 20, he had served for four years in the local temple as a therapeutes ("attendant" or "associate") of Asclepius. Although Galen studied the human body, dissection of human corpses was against Roman law, so instead he used pigs, apes, sheep, goats, and other animals. Through studying animal dissections, Galen applied his animal anatomy findings and developed a theory of human anatomy.

Galen moved to Rome in 162. There he lectured, wrote extensively, and performed public demonstrations of his anatomical knowledge. He soon gained a reputation as an experienced physician, attracting to his practice a large number of patients. Among them was the consul Flavius Boethius, who introduced him to the imperial court, where he became a physician to Emperor Marcus Aurelius. Despite being a member of the court, Galen reputedly shunned Latin, preferring to speak and write in his native Greek. He treated Roman emperors Lucius Verus, Commodus, and Septimius Severus. In 166, Galen returned to Pergamon, but went back to Rome for good in 169.

Galen followed Hippocrates' theory of the four humours, believing that one's health depended on the balance between the four main fluids of the body (blood, yellow bile, black bile, and phlegm). Food was believed to be the initial object that allowed the stabilization of these humours. By contrast, drugs, venesection, cautery and surgery were drastic and were to be used only when diet and regimen could no longer help. The survival and amendment of Hippocratic medicine is attributed to Galen, who coupled the four qualities of cold, heat, dry, and wet with the four main fluids of the body, would remain in health care for another millennia or so.

Galen wrote a short essay called "The Best Doctor Is Also A Philosopher", where he writes that a physician needs to be knowledgeable about not just the physical, but additionally logical and ethical philosophy. He writes that a physician "must be skilled at reasoning about the problems presented to him, must understand the nature and function of the body within the physician world, and must practice temperance and despise all money". The ideal physician treats both the poor and elite fairly and is a student of all that affects health. Galen thought that eleven years of study was an adequate amount of time to make a competent physician. He references Hippocrates throughout his writings, saying that Hippocratic literature is the basis for physicians' conduct and treatments. The writings of Galen survived longer than the writings of any other medical researchers of antiquity. Galen also wrote an astrological doctrine, De diebus decretorus (Critical Days Book III), in which he describes the importance of astrology in prognosis and diagnosis.

Asclepiades

Bust of Asclepiades

Asclepiades studied to be a physician in Alexandria and practiced medicine in Asia Minor as well as Greece before he moved to Rome in the 1st century BC. His knowledge of medicine allowed him to flourish as a physician. Asclepiades was a leading physician in Rome and was a close friend of Cicero.

He developed his own version of the molecular structure of the human body. Asclepiades' atomic model contained multi-shaped atoms that passed through bodily pores. These atoms were either round, square, triangular. Asclepiades noted that as long as the atoms were flowing freely and continuously, then the health of the human was maintained. He believed that if the atoms were too large or the pores were too constricted, then illness would present in multiple symptoms such as fever, spasms, or in more severe cases paralysis.

Asclepiades strongly believed in hot and cold baths as a remedy for illness; his techniques purposely did not inflict severe pain upon the patient. Asclepiades used techniques with the intent to cause the least amount of discomfort while continuing to cure the patient. His other remedies included music therapy to induce sedation, and consuming wine to cure headache and a fever. Asclepiades is the first documented physician in Rome to use massage therapy.

Aulus Cornelius Celsus

Celsus (25 BC–AD 50) was a Roman encyclopaedist who wrote a general encyclopaedia about many subjects. His exact place of birth as well as when he lived are unknown; however, it is known he lived during the reigns of Augustus and Tiberius. The only surviving work from his larger encyclopaedia is De Medicina. This work contains eight volumes, two of which are on surgery. De Medicina provides some of the best accounts of Roman medicine during his time. Its contents proved to be valuable even into the 15th century after Pope Nicolas V rediscovered it, becoming the first medical book to be published in 1478. It is still debated if he practiced medicine himself or just compiled the works of the time, much of it from Greek sources. This is important because at the time Greeks were looked down upon by the Romans and thus so was the work of doctors.

In his book he discussed the two different schools of thought at the time relating to medicine he calls "Empirics" and "Dogmatics". Empirics followed empirical observation while Dogmatics needed to understand the theory behind how a treatment works. Celsus is also credited with writing on four of the five characteristics of inflammation, redness (rubor), swelling (tumour), heat (calor), and pain (dolor). Galen would write about the fifth, loss of function (functio laesa).

Soranus

Soranus was a Greek physician born in Ephesus, who lived during the reigns of Trajan and Hadrian (98–138 AD). According to the Suda, he trained at the Alexandria School of Medicine and practiced in Rome. Soranus was a part of the Methodic school of Asclepiades, which fostered the ideals of the Hippocratic doctrine. He was the chief representative of the Methodic school of physicians. Soranus's most notable work was his book gynaecology, in which he discussed many topics that are considered modern ideas such as birth control, pregnancy, midwife's duties, and post-childbirth care. His treatise Gynaecology is extant (first published in 1838, later by V. Rose, in 1882, with a 6th-century Latin translation by Muscio, a physician of the same school). He accounts for the internal difficulties that could arise during labor from both the mother and the fetus. He also did work with fractures, surgery, and embryology.

Hospitals

Plan of valetudinarium, near Düsseldorf, Germany. Late 1st century

The Roman medical system saw the establishment of the first hospitals; these were reserved for slaves and soldiers. Physicians were assigned to follow armies or ships, tending to the injured. In Rome, death was caused by a combination of poor sanitation, famine, disease, epidemics, malnutrition, and warfare that led to high Roman mortality rates. The development of health services was prolonged by the unsympathetic attitudes of the Romans towards the sick, superstition, and religious beliefs.

Ancient Roman hospitals were established by the 1st century BC as military hospitals known as valetudinaria. The valetudinaria began as a small cluster of tents and fortresses dedicated to wounded soldiers. The original hospitals were built along major roads, and soon became part of Roman fort architecture. They were usually placed near the outer wall in a quiet part of the fortification. The earliest known Roman hospitals of the Roman Empire were built in the 1st and 2nd centuries AD, in the reign of the emperor Trajan. The Roman military established these hospitals, as the army's expansion beyond the Italian Peninsula meant that the wounded could no longer be cared for in private homes. Over time, the temporary forts developed into permanent facilities. It is possible that some valteduinaria were established at earlier parts of history. They may also have been established by Julius Caesar. Other hospitals were possibly built during the reign of Augustus or Claudius.

Capsarii tending to injured soldiers depicted on Trajan's Column

Valetudinaria were field hospitals or flying military camps primarily used to treat soldiers in the military. Access to these hospitals was likely an important perk of military service. The care these institutions provided was likely highly professional for the time, and they were capable of holding up to 200 patients. Celsus describes these hospitals as large and staffed by "over-worked doctors". These over-worked doctors were known as the medici. Alongside the medici, there was a group of veterinarians, administrators, and wound dressers, known as veteranarii, optio valetudinarii, and capsarii respectively. Other hospitals were designed to care for slaves. Slave valetudinaria were of lower quality then the military hospitals, with less equipment and poorer doctors. Roman writers compared these institutions to veterinary care, and equated the treatment these hospitals gave to barbarity.

A standard valetudinarium was a rectangular building consisting of four wings, connected by an entrance hall that could be used as a triage center. Each legion's hospital was constructed to accommodate 6% to 10% of the legion's 5,000 men. The building also included a large hall, reception ward, dispensary, kitchen, staff quarters, and washing and latrine facilities. All of these hospitals were the exact same shape and layout, and one was located in every castra.

Doctors could also set up public clinics in tabernae. Tabernae were another way of getting medical attention in ancient Rome. These facilities very expensive, and there was no inpatient care. This method was rare, it was far more common for the physician to arrive at the patient's house. People who could not afford a doctor or go to a valetudinaria would pray at a temple of Asclepius, the Roman god of medicine, for healing.

Surgery

Roman surgical instruments found at Pompeii
 

Surgery was typically used as a last resort because of the risks involved. When surgery did happen though, it was usually limited to the surface of the body because doctors recognized that injuries regarding the body's most important physiological functions (brain, heart, spine, etc.) could not usually be treated. There were a variety of surgical tools in ancient Rome. For example, bone levers were tools used to remove diseased bone tissue from the skull and to remove foreign objects (such as a weapon) from a bone. The ancient Romans were capable of performing techniques like cataract surgery and caesarean sections. They also could perform more outdated procedures such as bloodletting. Ancient Roman surgery was developed in the 2nd century from Greek techniques by doctors such as Galen.

Medicines

Diet

Correct diet was seen as essential to healthy living. Food was perceived to have a healing effect or a causative effect on disease, determined by its impact on the humors; as well as preventing disease. Some of these foods included rice, chic peas, and olives, which were widely used by the Roman military. At an archaeological site, other plants were found that were used for medicinal purposes such as lentils, garden peas, and figs. A variety of meats were also discovered at the site which were believed to be used for sick individuals. Poultry, eggs, and oysters were used as a diet for those with health issues. Moderation of foods was key to healthy living and gave rise to healthy eating philosophies. When diet no longer promoted health, drugs, phlebotomy, cautery, or surgery were used. Patients having control of their lives, managing their own preventative medical diets, and the freedom to seek physicians, indicates that patient autonomy was valued.

Herbal and other medicines

Roman physicians used a wide range of herbal and other medicines. Their ancient names, often derived from Greek, do not necessarily correspond to individual modern species, even if these have the same names. Known medicines include:

Roman medicines, according to Dioscorides
Probable
substance
Latin/Greek
name
Indication and Effects
Fennel Ippomarathron Cures painful urination; expels menstrual flow; stops bowel discharge; brings out breast milk; breaks kidney and urinary stones
Rhubarb Ra For flatulence, convulsions, internal disorders (stomach, spleen, liver, kidneys, womb, peritoneum), sciatica, asthma, rickets, dysentery, etc.
Gentian Gentiane Warming, astringent; for poisonous bites, liver disorders; induces abortion; treats deep ulcers, eye inflammation
Birthwort Aristolochia Poisonous; assists in childbirth
Liquorice Glukoriza Calms stomach; chest, liver, kidney and bladder disorders
Aloe Aloe Heals wounds (applied dry); removes boils; purgative; treats alopecia

Statues and healing shrines were sites of prayer and sacrifice for both the poor and the elite, and were common throughout the Roman Empire. Reverence for shrines and statues reflected a search for healing, guidance, and alternatives to ineffectual human physicians and drugs.

In 2013, Italian scientists studied the content of a Roman shipping vessel, known as the Relitto del Pozzino, sank off the coast of Populonia, Tuscany around 120 BC, which was excavated during the 1980s and 90s. The vessel had a medicine chest with pyxides inside, which contained medicinal tablets or pills full of a number of zinc compounds, as well as iron oxide, starch, beeswax, pine resin and other plant-derived materials, all probably served as some sort of eye medicine or eyewash.

Treatments

Healing sanctuaries

A physician's overall goal was to help those afflicted by disease or injury as best as they could; the physician's credibility rested on their successful cures. Of course they could not reliably cure ailments; sometimes the best they could hope for was that their treatments did not worsen their patients' problems. Many physicians were criticised by their peers for their inability to cure an apparently simple illness. Gaps in physician-provided care were filled with several types of supernatural healthcare; the Romans believed in the power of divine messages and healing. There have been descriptions of many gods from multiple religions that dealt with destruction or healing. For example, in 431 BC, in response to the plague running rampant all over the country of Italy, the temple of the Apollo Medicus was accredited with an influence of healing.

Altar in the temple of Aesculapius, Pompeii, Italy

Scattered across Greco-Roman and Egyptian history are descriptions of healing sanctuaries dedicated to the various healing gods. Sick or injured Romans would often flock to Asclepieia, temples dedicated to Asclepius, the god of healing, as it was believed that the god actually inhabited the sanctuary and would provide divine healing to supplicants. The process itself was simple: the sick person would give a specified donation to the temple, and then undergo a process called "incubation" in which they would relocate to a special room where the god would be able to contact them, often through dreams in which the god would either prescribe care or provide it themselves. Often the type of cure prescribed would be rather similar to the actual medical practices of physicians of the time. This type of supernatural care did not conflict with mainstream healthcare. Physicians would often recommend that patients go to a healing sanctuary when they were afflicted by an illness that the physician could not cure. This allowed the reputation of the physician to remain unharmed, as it was seen more as a referral than as a failure.

Stab wounds

Roman physicians tried their best to help treat battlefield wounds. Celsus describes treatments early Roman doctors used for battlefield abdominal wounds. Celsus describes that doctors should first observe the color of the intestines to see that if they are “...livid or pallid or black…” in which case treatment is impossible. If the large intestine is found to be cut he says treatment is unlikely to be successful but suggests suturing the intestine. Treatment of abdominal wounds should occur quickly and for fear exposed intestines would dry out. Celsus suggests adding water to the intestines to prevent this. The Romans also knew about the delicate care needed for such complex wounds. Assistants with surgical hooks were used to stitch up large abdominal wounds. They were used to help separate the margins of the abdomen because both the inner membrane and the surface skin needed to be sutured with two sets of stitches because it could be broken easily. The Romans applied a variety of ointments and dressings to these wounds. Celsus describes 34 different ones.

Colostrum

Colostrum is the first form of milk produced by lactating mammals. Both Greek and Roman medical texts prescribe the use of a variety of substances, of varying medical and religious significance. Several substances, such as sulfur, asphalt and animal excrement, were associated with the practice of human purification. The practice of using a woman's breast milk as a medicine has very early roots in Egyptian medical texts. In several such texts there are references to the use of the milk of a woman who has given birth to a male child. This practice is said to be based on depictions in several statues of the goddess Isis breastfeeding her son, the god Horus. Both Egyptian and Greek texts state that the milk used for medicinal purposes should be strictly from a woman who has borne a male child. The treatments using breast milk differed vastly between Greek and Roman culture. In Greek medicine, milk was very rarely actually consumed. Instead, it was used in recipes for ointments and washes that would treat burns and other skin-related maladies. These treatments were exclusively given to women, as women's bodies were viewed as "polluted" in some sense. In stark contrast, the Roman use of colostrum was more widespread and varied. Stories suggest that adults drinking breast milk was viewed as socially acceptable, but was not common unless used for treatment. The milk was instead ingested by the patient, and the treatment was given to both men and women, which then allowed the views of the female body to be viewed as analogous compared to their male peers, rather than as the opposites they have been for centuries before. In general, while not every single fear about the changing medical views of female physiology went away, the Romans then seemed less concerned about the so-called "pollution" of a woman's body and therefore need to have the women have special requirements needed for "purification."

It has been shown in modern times that having patients ingest mother's milk (or colostrum) is actually a rather effective treatment due to the benefits associated with it. For example, the use of colostrum has been shown to prevent the growth of Staphylococcus bacteria, which are a known cause of several types of infection. Colostrum is about half as effective as some antibiotics prescribed to patients today. Colostrum is also effective against the bacterium chlamydia. Chlamydia is a sexually transmitted disease in which some subtypes of it can cause trachoma, which is a major source of cause for severe sight impairment, if not blindness. Colostrum was a reasonably effective treatment for Chlamydia in the absence of other antibiotics.

Diagnostic methods

Dreams

Dream interpretation was another avenue for treatment of illnesses by physicians. Often the interpretations of a patient's dreams would actually determine what treatment they received. A Hippocratic work titled Regimen in Acute Diseases details much of the principles outlined by Galen: specifically the humors and examples of how they could be used to prescribe treatment. The theme of this method is knowing the patient. To know how to treat a person, the physician must become familiar with and interpret the important aspects of their lives: the climate, their food intake, how much they sleep, how much they drink, any injuries. They would then draw conclusions about the patient and what must be done to set them back to equilibrium. The fourth book of the Regimen is the earliest mention of the topic of dream medicine. Dreams were used by physicians in diagnosis. They added another layer of depth to the physician's investigation of the patient. The soul was thought to serve the purpose that the brain has been discovered to serve. Sensation, pain, motion and other physiological concepts were thought to be the work of the soul. It was also thought that the soul continues the work of bodily upkeep even when a person is sleeping. Thus, dreams would show what ailed a person.

There were two types of dreams associated with medicine: prophetic and diagnostic. Prophetic dreams were divine in origin and foretold good or bad tidings for the future. Diagnostic dreams were a result of the soul telling what afflicted the body. If the dreams were of normal everyday events, their body was healthy and in equilibrium. The farther from the norm, and the more chaotic the dreams were, the more ill the patient was. The treatments that were recommended addressed what the dreams showed, and attempted to set the body right through consumption of food that carried the correct humor characteristics.

Astro-medicine

Galen wrote a treatise on diagnosis and prognosis by celestial movement. This ancient medical practice associated that disease and parts of the body were affected by the movement or location of the sun, moon and planets. This is similar to horoscopic astrology and the notion of astrological signs. These celestial signs were only a part of the process in his work Critical Days. Galen also includes that the patients' feces, urine, sputum should be examined for diagnosis. He states that examination of the excrement could indicate a disease of the respirator system, urinary tract or vascular system. Many physicians at the time believed in the association of astrology and medicine. Book III of Galen's writing he correlates the lunar phases which cause changes in the tides to also cause changes the fluid humors in the body. He also makes reference to "medical months", which are based on the two periods of the moons which are about two calendar months. There were also days that were considered critical including day seven, fourteen and day twenty which were considered favorable for a medical crisis to occur.

Textual transmission

Dioscorides De materia medica in Arabic; Spain, 12th–13th century

Galenic medical texts embody the written medical tradition of classical antiquity. Little written word has survived from before that era. The volume of Galen's extant written works, however, is nearly 350 – far surpassing any other writer of the period. Prior to Galen, much of medical knowledge survived through word of mouth. The tradition of transmission and translation originated with the De materia medica, an encyclopaedia written by Pedanius Dioscorides between 50 and 70 AD. Dioscorides was a Roman physician of Greek descent. The manuscripts classified and illustrated over 1000 substances and their uses.

De materia medica influenced medical knowledge for centuries, due to its dissemination and translation into Greek, Arabic, and Latin. Galen wrote in Greek, but Arabic and Syriac translations survived as well. He referenced and challenged written works by Hippocratic physicians and authors, which gave insight into other popular medical philosophies. Herophilus, known for his texts on anatomy through dissection, and Erasistratus, also known for anatomy and physiology, survive through Galenic reference. Galen also referenced the written works of Soranus, a physician of the Methodic school known for his four-book treatise on gynecology. His synthesis of earlier medical philosophies and broad range of subjects produced the textual legacy that Galen left for the medical community for the next 1500 years.

Word processor

From Wikipedia, the free encyclopedia
 
WordPerfect, a word processor first released for minicomputers in 1979 and later ported to microcomputers, running on Windows XP
 
LibreOffice Writer, one of the most popular free and open-source word processors

A word processor (WP) is a device or computer program that provides for input, editing, formatting, and output of text, often with some additional features.

Early word processors were stand-alone devices dedicated to the function, but current word processors are word processor programs running on general purpose computers.

The functions of a word processor program fall somewhere between those of a simple text editor and a fully functioned desktop publishing program. However, the distinctions between these three have changed over time and were unclear after 2010.

Background

Word processors did not develop out of computer technology. Rather, they evolved from mechanical machines and only later did they merge with the computer field. The history of word processing is the story of the gradual automation of the physical aspects of writing and editing, and then to the refinement of the technology to make it available to corporations and Individuals.

The term word processing appeared in American offices in early 1970s centered on the idea of streamlining the work to typists, but the meaning soon shifted toward the automation of the whole editing cycle.

At first, the designers of word processing systems combined existing technologies with emerging ones to develop stand-alone equipment, creating a new business distinct from the emerging world of the personal computer. The concept of word processing arose from the more general data processing, which since the 1950s had been the application of computers to business administration.

Through history, there have been three types of word processors: mechanical, electronic and software.

Mechanical word processing

The first word processing device (a "Machine for Transcribing Letters" that appears to have been similar to a typewriter) was patented by Henry Mill for a machine that was capable of "writing so clearly and accurately you could not distinguish it from a printing press". More than a century later, another patent appeared in the name of William Austin Burt for the typographer. In the late 19th century, Christopher Latham Sholes created the first recognizable typewriter although it was a large size, which was described as a "literary piano".

The only "word processing" these mechanical systems could perform was to change where letters appeared on the page, to fill in spaces that were previously left on the page, or to skip over lines. It was not until decades later that the introduction of electricity and electronics into typewriters began to help the writer with the mechanical part. The term “word processing” (translated from the German word Textverarbeitung) itself was created in the 1950s by Ulrich Steinhilper, a German IBM typewriter sales executive. However, it did not make its appearance in 1960s office management or computing literature (an example of grey literature), though many of the ideas, products, and technologies to which it would later be applied were already well known. Nonetheless by 1971 the term was recognized by the New York Times as a business "buzz word". Word processing paralleled the more general "data processing", or the application of computers to business administration.

Thus by 1972 discussion of word processing was common in publications devoted to business office management and technology, and by the mid-1970s the term would have been familiar to any office manager who consulted business periodicals.

Electromechanical and electronic word processing

By the late 1960s, IBM had developed the IBM MT/ST (Magnetic Tape/Selectric Typewriter). This was a model of the IBM Selectric typewriter from the earlier part of this decade, but it came built into its own desk, integrated with magnetic tape recording and playback facilities along with controls and a bank of electrical relays. The MT/ST automated word wrap, but it had no screen. This device allowed a user to rewrite text that had been written on another tape, and it also allowed limited collaboration in the sense that a user could send the tape to another person to let them edit the document or make a copy. It was a revolution for the word processing industry. In 1969, the tapes were replaced by magnetic cards. These memory cards were inserted into an extra device that accompanied the MT/ST, able to read and record users' work.

In the early 1970s, word processing began to slowly shift from glorified typewriters augmented with electronic features to become fully computer-based (although only with single-purpose hardware) with the development of several innovations. Just before the arrival of the personal computer (PC), IBM developed the floppy disk. In the early 1970s, the first word-processing systems appeared which allowed display and editing of documents on CRT screens.

During this era, these early stand-alone word processing systems were designed, built, and marketed by several pioneering companies. Linolex Systems was founded in 1970 by James Lincoln and Robert Oleksiak. Linolex based its technology on microprocessors, floppy drives and software. It was a computer-based system for application in the word processing businesses and it sold systems through its own sales force. With a base of installed systems in over 500 sites, Linolex Systems sold 3 million units in 1975 — a year before the Apple computer was released.

At that time, the Lexitron Corporation also produced a series of dedicated word-processing microcomputers. Lexitron was the first to use a full-sized video display screen (CRT) in its models by 1978. Lexitron also used 514 inch floppy diskettes, which became the standard in the personal computer field. The program disk was inserted in one drive, and the system booted up. The data diskette was then put in the second drive. The operating system and the word processing program were combined in one file.

Another of the early word processing adopters was Vydec, which created in 1973 the first modern text processor, the “Vydec Word Processing System”. It had built-in multiple functions like the ability to share content by diskette and print it. The Vydec Word Processing System sold for $12,000 at the time, (about $60,000 adjusted for inflation).

The Redactron Corporation (organized by Evelyn Berezin in 1969) designed and manufactured editing systems, including correcting/editing typewriters, cassette and card units, and eventually a word processor called the Data Secretary. The Burroughs Corporation acquired Redactron in 1976.

A CRT-based system by Wang Laboratories became one of the most popular systems of the 1970s and early 1980s. The Wang system displayed text on a CRT screen, and incorporated virtually every fundamental characteristic of word processors as they are known today. While early computerized word processor system were often expensive and hard to use (that is, like the computer mainframes of the 1960s), the Wang system was a true office machine, affordable to organizations such as medium-sized law firms, and easily mastered and operated by secretarial staff.

The phrase "word processor" rapidly came to refer to CRT-based machines similar to Wang's. Numerous machines of this kind emerged, typically marketed by traditional office-equipment companies such as IBM, Lanier (AES Data machines - re-badged), CPT, and NBI. All were specialized, dedicated, proprietary systems, with prices in the $10,000 range. Cheap general-purpose personal computers were still the domain of hobbyists.

Japanese word processor devices

In Japan, even though typewriters with Japanese writing system had widely been used for businesses and governments, they were limited to specialists who required special skills due to the wide variety of letters, until computer-based devices came onto the market. In 1977, Sharp showcased a prototype of a computer-based word processing dedicated device with Japanese writing system in Business Show in Tokyo.

World-first Japanese word processor Toshiba JW-10 (Launched in February 1979, Toshiba Science Institute)

Toshiba released the first Japanese word processor JW-10 in February 1979. The price was 6,300,000 JPY, equivalent to US$45,000. This is selected as one of the milestones of IEEE.

Toshiba Rupo JW-P22(K)(March 1986) and an optional micro floppy disk drive unit JW-F201
 
Sharp Shoin WD-J150

The Japanese writing system uses a large number of kanji (logographic Chinese characters) which require 2 bytes to store, so having one key per each symbol is infeasible. Japanese word processing became possible with the development of the Japanese input method (a sequence of keypresses, with visual feedback, which selects a character) -- now widely used in personal computers. Oki launched OKI WORD EDITOR-200 in March 1979 with this kana-based keyboard input system. In 1980 several electronics and office equipment brands entered this rapidly growing market with more compact and affordable devices. While the average unit price in 1980 was 2,000,000 JPY (US$14,300), it was dropped to 164,000 JPY (US$1,200) in 1985. Even after personal computers became widely available, Japanese word processors remained popular as they tended to be more portable (an "office computer" was initially too large to carry around), and become necessities in business and academics, even for private individuals in the second half of the 1980s. The phrase "word processor" has been abbreviated as "Wa-pro" or "wapuro" in Japanese.

Word processing software

The final step in word processing came with the advent of the personal computer in the late 1970s and 1980s and with the subsequent creation of word processing software. Word processing software that would create much more complex and capable output was developed and prices began to fall, making them more accessible to the public. By the late 1970s, computerized word processors were still primarily used by employees composing documents for large and midsized businesses (e.g., law firms and newspapers). Within a few years, the falling prices of PCs made word processing available for the first time to all writers in the convenience of their homes.

The first word processing program for personal computers (microcomputers) was Electric Pencil, from Michael Shrayer Software, which went on sale in December 1976. In 1978 WordStar appeared and because of its many new features soon dominated the market. However, WordStar was written for the early CP/M (Control Program–Micro) operating system, and by the time it was rewritten for the newer MS-DOS (Microsoft Disk Operating System), it was obsolete. WordPerfect and its competitor Microsoft Word replaced it as the main word processing programs during the MS-DOS era, although there were less successful programs such as XyWrite.

Most early word processing software required users to memorize semi-mnemonic key combinations rather than pressing keys such as "copy" or "bold". Moreover, CP/M lacked cursor keys; for example WordStar used the E-S-D-X-centered "diamond" for cursor navigation. However, the price differences between dedicated word processors and general-purpose PCs, and the value added to the latter by software such as “killer app” spreadsheet applications, e.g. VisiCalc and Lotus 1-2-3, were so compelling that personal computers and word processing software became serious competition for the dedicated machines and soon dominated the market.

Then in the late 1980s innovations such as the advent of laser printers, a "typographic" approach to word processing (WYSIWYG - What You See Is What You Get), using bitmap displays with multiple fonts (pioneered by the Xerox Alto computer and Bravo word processing program), and graphical user interfaces such as “copy and paste” (another Xerox PARC innovation, with the Gypsy word processor). These were popularized by MacWrite on the Apple Macintosh in 1983, and Microsoft Word on the IBM PC in 1984. These were probably the first true WYSIWYG word processors to become known to many people. Of particular interest also is the standardization of TrueType fonts used in both Macintosh and Windows PCs. While the publishers of the operating systems provide TrueType typefaces, they are largely gathered from traditional typefaces converted by smaller font publishing houses to replicate standard fonts. Demand for new and interesting fonts, which can be found free of copyright restrictions, or commissioned from font designers, occurred.

The growing popularity of the Windows operating system in the 1990s later took Microsoft Word along with it. Originally called "Microsoft Multi-Tool Word", this program quickly became a synonym for “word processor”.

Neuroscience of religion

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