Environmental characteristics.

Light.

Natural light does not penetrate the deep ocean, with the exception of the upper parts of the mesopelagic. Since photosynthesis is not possible, plants and phytoplankton cannot live in this zone, and as these are the primary producers of almost all of earth's ecosystems, life in this area of the ocean must depend on energy sources from elsewhere. Except for the areas close to the hydrothermal vents, this energy comes from organic material drifting down from the photic zone. The sinking organic material is composed of algal particulates, detritus, and other forms of biological waste, which is collectively referred to as marine snow.

Pressure.

Because pressure in the ocean increases by about 1 atmosphere for every 10 meters of depth, the amount of pressure experienced by many marine organisms is extreme. Until recent years, the scientific community lacked detailed information about the effects of pressure on most deep sea organisms because the specimens encountered arrived at the surface dead or dying and weren't observable at the pressures at which they lived. With the advent of traps that incorporate a special pressure-maintaining chamber, undamaged larger metazoan animals have been retrieved from the deep sea in good condition.

Salinity.

Salinity is remarkably constant throughout the deep sea, at about 35 parts per thousand. There are some minor differences in salinity, but none that are ecologically significant, except in the Mediterranean and Red Seas.

Temperature.

The two areas of greatest temperature gradient in the oceans are the transition zone between the surface waters and the deep waters, the thermocline, and the transition between the deep-sea floor and the hot water flows at the hydrothermal vents. Thermoclines vary in thickness from a few hundred meters to nearly a thousand meters. Below the thermocline, the water mass of the deep ocean is cold and far more homogeneous. Thermoclines are strongest in the tropics, where the temperature of the epipelagic zone is usually above 20 °C. From the base of the epipelagic, the temperature drops over several hundred meters to 5 or 6 °C at 1,000 meters. It continues to decrease to the bottom, but the rate is much slower. The cold water stems from sinking heavy surface water in the polar regions.  At any given depth, the temperature is practically unvarying over long periods of time, without seasonal changes and with very little interannual variability. No other habitat on earth has such a constant temperature.  In hydrothermal vents the temperature of the water as it emerges from the "black smoker" chimneys may be as high as 400 °C (it is kept from boiling by the high hydrostatic pressure) while within a few meters it may be back down to 2 to 4 °C.

Biology.

Regions below the epipelagic are divided into further zones, beginning with the "mesopelagic" which spans from 200 to 1000 meters below sea level, where so little light penetrates that primary production becomes impossible. Below this zone the deep sea begins, consisting of the aphotic "bathypelagic", "abyssopelagic" and "hadopelagic". Food consists of falling organic matter known as'marine snow' and carcasses derived from the productive zone above, and is scarce both in terms of spatial and temporal distribution.  Instead of relying on gas for their buoyancy, many deep-sea species have jelly-like flesh consisting mostly of glycosaminoglycans, which provides them with very low density. It is also common among deep water squid to combine the gelatinous tissue with a flotation chamber filled with a coelomic fluid made up of the metabolic waste product ammonium chloride, which is lighter than the surrounding water.  The midwater fish have special adaptations to cope with these conditions—they are small, usually being under ; they have slow metabolisms and unspecialized diets, preferring to sit and wait for food rather than waste energy searching for it. They have elongated bodies with weak, watery muscles and skeletal structures. They often have extendable, hinged jaws with recurved teeth. Because of the sparse distribution and lack of light, finding a partner with which to breed is difficult, and many organisms are hermaphroditic.  Because light is so scarce, fish often have larger than normal, tubular eyes with only rod cells. Their upward field of vision allows them to seek out the silhouette of possible prey. Prey fish however also have adaptations to cope with predation. These adaptations are mainly concerned with reduction of silhouettes, a form of camouflage. The two main methods by which this is achieved are reduction in the area of their shadow by lateral compression of the body, and counter illumination via bioluminescence. This is achieved by production of light from ventral photophores, which tend to produce such light intensity to render the underside of the fish of similar appearance to the background light. For more sensitive vision in low light, some fish have a retroreflector behind the retina. Flashlight fish have this plus photophores, which combination they use to detect eyeshine in other fish (see "tapetum lucidum").  Organisms in the deep sea are almost entirely reliant upon sinking living and dead organic matter which falls at approximately 100 meters per day. In addition, only about 1 to 3% of the production from the surface reaches the sea bed mostly in the form of marine snow. Larger food falls, such as whale carcasses, also occur and studies have shown that these may happen more often than currently believed. There are many scavengers that feed primarily or entirely upon large food falls and the distance between whale carcasses is estimated to only be 8 kilometers. In addition, there are a number of filter feeders that feed upon organic particles using tentacles, such as "Freyella elegans".  Marine bacteriophages play an important role in cycling nutrients in deep sea sediments. They are extremely abundant (between 5x10 and 1x10 phages per square meter) in sediments around the world.  Despite being so isolated deep sea organisms have still been harmed by human interaction with the oceans. The London Convention aims to protect the marine environment from dumping of wastes such as sewage sludge and radioactive waste. A study found that at one region there had been a decrease in deep sea coral from 2007 to 2011, with the decrease being attributed to global warming and ocean acidification, and biodiversity estimated as being at the lowest levels in 58 years. Ocean acidification is particularly harmful to deep sea corals because they are made of aragonite, an easily soluble carbonate, and because they are particularly slow growing and will take years to recover. Deep sea trawling is also harming the biodiversity by destroying deep sea habitats which can take years to form. Another human activity that has altered deep sea biology is mining. One study found that at one mining site fish populations had decreased at six months and at three years, and that after twenty six years populations had returned to the same levels as prior to the disturbance.

Chemosynthesis.

There are a number of species that do not primarily rely upon dissolved organic matter for their food and these are found at hydrothermal vents. One example is the symbiotic relationship between the tube worm "Riftia" and chemosynthetic bacteria. It is this chemosynthesis that supports the complex communities that can be found around hydrothermal vents. These complex communities are one of the few ecosystems on the planet that do not rely upon sunlight for their supply of energy.

Exploration.

The deep sea is one of the less explored areas on Earth. Pressures even in the mesopelagic become too great for traditional exploration methods, demanding alternative approaches for deep sea research. Baited camera stations, small manned submersibles and ROVs (remotely operated vehicles) are three methods utilized to explore the ocean's depths. Because of the difficulty and cost of exploring this zone, current knowledge is limited. Pressure increases at approximately one atmosphere for every 10 meters meaning that some areas of the deep sea can reach pressures of above 1,000 atmospheres. This not only makes great depths very difficult to reach without mechanical aids, but also provides a significant difficulty when attempting to study any organisms that may live in these areas as their cell chemistry will be adapted to such vast pressures.

The deep sea or deep layer is the lowest layer in the ocean, existing below the thermocline and above the seabed, at a depth of 1000 fathoms (1800 m) or more. Little or no light penetrates this part of the ocean, and most of the organisms that live there rely for subsistence on falling organic matter produced in the photic zone. For this reason, scientists once assumed that life would be sparse in the deep ocean, but virtually every probe has revealed that, on the contrary, life is abundant in the deep ocean. From the time of Pliny until the late nineteenth century...humans believed there was no life in the deep. It took a historic expedition in the ship "Challenger" between 1872 and 1876 to prove Pliny wrong; its deep-sea dredges and trawls brought up living things from all depths that could be reached. Yet even in the twentieth century scientists continued to imagine that life at great depth was insubstantial, or somehow inconsequential. The eternal dark, the almost inconceivable pressure, and the extreme cold that exist below one thousand meters were, they thought, so forbidding as to have all but extinguished life. The reverse is in fact true...(Below 200 meters) lies the largest habitat on earth.

在海洋学上,深海是指透光层以下的海,一般指200米以下。因为不透光,没办法行光合作用,没有行光合作用的生产者,故深海的生物密度较浅海来的少。


Measures.

A measure of statistical dispersion is a nonnegative real number that is zero if all the data are the same and increases as the data become more diverse.  Most measures of dispersion have the same units as the quantity being measured. In other words, if the measurements are in metres or seconds, so is the measure of dispersion. Examples of dispersion measures include: These are frequently used (together with scale factors) as estimators of scale parameters, in which capacity they are called estimates of scale. Robust measures of scale are those unaffected by a small number of outliers, and include the IQR and MAD.  All the above measures of statistical dispersion have the useful property that they are "location-invariant" and "linear in scale". This means that if a random variable "X" has a dispersion of "S" then a linear transformation "Y" = "aX" + "b" for real "a" and "b" should have dispersion "S" = |"a"|"S", where |"a"| is the absolute value of "a", that is, ignores a preceding negative sign "–".  Other measures of dispersion are dimensionless. In other words, they have no units even if the variable itself has units. These include:  There are other measures of dispersion:  Some measures of dispersion have specialized purposes, among them the Allan variance and the Hadamard variance.  For categorical variables, it is less common to measure dispersion by a single number; see qualitative variation. One measure that does so is the discrete entropy.

Sources.

In the physical sciences, such variability may result from random measurement errors: instrument measurements are often not perfectly precise, i.e., reproducible, and there is additional inter-rater variability in interpreting and reporting the measured results. One may assume that the quantity being measured is stable, and that the variation between measurements is due to observational error. A system of a large number of particles is characterized by the mean values of a relatively few number of macroscopic quantities such as temperature, energy, and density. The standard deviation is an important measure in fluctuation theory, which explains many physical phenomena, including why the sky is blue.  In the biological sciences, the quantity being measured is seldom unchanging and stable, and the variation observed might additionally be "intrinsic" to the phenomenon: It may be due to "inter-individual variability", that is, distinct members of a population differing from each other. Also, it may be due to intra-individual variability, that is, one and the same subject differing in tests taken at different times or in other differing conditions. Such types of variability are also seen in the arena of manufactured products; even there, the meticulous scientist finds variation.  In economics, finance, and other disciplines, regression analysis attempts to explain the dispersion of a dependent variable, generally measured by its variance, using one or more independent variables each of which itself has positive dispersion. The fraction of variance explained is called the coefficient of determination.

A partial ordering of dispersion.

A mean-preserving spread (MPS) is a change from one probability distribution A to another probability distribution B, where B is formed by spreading out one or more portions of A's probability density function while leaving the mean (the expected value) unchanged. The concept of a mean-preserving spread provides a partial ordering of probability distributions according to their dispersions: of two probability distributions, one may be ranked as having more dispersion than the other, or alternatively neither may be ranked as having more dispersion.

In statistics, dispersion (also called variability, scatter, or spread) is the extent to which a distribution is stretched or squeezed. Common examples of measures of statistical dispersion are the variance, standard deviation, and interquartile range.

在统计学里,离散程度(英语:statistical dispersion)或变差(英语:variation)是指一个分布或随机变量的压缩和拉伸的程度。用以描述离散程度或变差的量主要有方差、标准差、变差系数和四分位距等。


History.

Speed control was used in automobiles as early as 1900 in the Wilson-Pilcher and also in the 1910s by Peerless. Peerless advertised that their system would "maintain speed whether up hill or down". The technology was adopted by James Watt and Matthew Boulton in 1788 to control steam engines, but the use of governors dates at least back to the 17th century. On an engine the governor adjusts the throttle position as the speed of the engine changes with different loads, so as to maintain a near constant speed.  Modern cruise control (also known as a speedostat or tempomat) was invented in 1948 by the inventor and mechanical engineer Ralph Teetor. His idea was ostensibly borne out of the frustration of riding in a car driven by his lawyer, who kept speeding up and slowing down as he talked. More significant factor in developing this device was the speed limit imposed across the US during World War II to save on gasoline use and reduce tire wear. A mechanism controlled by the driver provided resistance to further pressure on the accelerator pedal when the vehicle reaching the desired speed. Teetor's idea of a dashboard speed selector with a mechanism connected to the drive shaft and a device able to push against the gas pedal was patented in 1950. He added a speed lock capability that would maintain the car's speed until the driver tapped the brake pedal or turned off the system.  The first car with Teetor's "Speedostat" system was the 1958 Imperial (called "Auto-pilot") using a speed dial on the dashboard. This system calculated ground speed based on driveshaft rotations off the rotating speedometer-cable, and used a bi-directional screw-drive electric motor to vary throttle position as needed. It was Cadillac Division that re-named the "Speedostat" and marketed the device as "Cruise Control."  A 1955 U.S. Patent for a "Constant Speed Regulator" was filed in 1950 by M-Sgt Frank J. Riley. He installed his invention, which he conceived while driving on the Pennsylvania Turnpike, on his own car in 1948. Another inventor named Harold Exline, working independently of Riley, also invented a type of cruise control, which he first installed on his own car and on cars belonging to friends of his. Exline filed a U.S. Patent for "Vacuum Powered Throttle Control With Electrically Controlled Air Valve" in 1951, and the Patent was granted in 1956. Despite these patents, Riley, Exline, and the subsequent patent holders were not able to collect royalties for any of the inventions using cruise control.  In 1965, American Motors Corporation (AMC) introduced a low-priced automatic speed control for its large-sized cars with automatic transmissions. The AMC "Cruise-Command" unit was engaged by a push-button once the desired speed was reached and then the throttle position was adjusted by a vacuum control directly from the speedometer cable rather than a separate dial on the dashboard.  Daniel Aaron Wisner invented "Automotive Electronic Cruise Control" in 1968 as an engineer for RCA's Industrial and Automation Systems Division in Plymouth, Michigan. His invention described in two patents filed that year (US 3570622 & US 3511329), with the second modifying his original design by debuting digital memory, was the first electronic device in controlling a car. Two decades passed before an integrated circuit for his design was developed by Motorola as the MC14460 Automotive Speed Control Processor in CMOS. The advantage of electronic speed control over its mechanical predecessor was that it could be integrated with electronic accident avoidance and engine management systems.  Following the 1973 oil crisis and rising fuel prices, the device became more popular in the U.S. "Cruise control can save gas by avoiding surges that expel fuel" while driving at steady speeds. In 1974, AMC, GM, and Chrysler priced the option at $60 to $70, while Ford charged $103.

Operation.

The driver must bring the vehicle up to speed manually and use a button to set the cruise control to the current speed.  The cruise control takes its speed signal from a rotating driveshaft, speedometer cable, wheel speed sensor from the engine's RPM, or from internal speed pulses produced electronically by the vehicle. Most systems do not allow the use of the cruise control below a certain speed - typically around. The vehicle will maintain the desired speed by pulling the throttle cable with a solenoid, a vacuum driven servomechanism, or by using the electronic systems built into the vehicle (fully electronic) if it uses a 'drive-by-wire' system.  All cruise control systems must be capable of being turned off both explicitly and automatically when the driver depresses the brake, and often also the clutch. Cruise control often includes a memory feature to resume the set speed after braking, and a coast feature to reduce the set speed without braking. When the cruise control is engaged, the throttle can still be used to accelerate the car, but once the pedal is released the car will then slow down until it reaches the previously set speed.  On the latest vehicles fitted with electronic throttle control, cruise control can be easily integrated into the vehicle's engine management system. Modern "adaptive" systems (see below) include the ability to automatically reduce speed when the distance to a car in front, or the speed limit, decreases. This is an advantage for those driving in unfamiliar areas.  The cruise control systems of some vehicles incorporate a "speed limiter" function, which will not allow the vehicle to accelerate beyond a pre-set maximum; this can usually be overridden by fully depressing the accelerator pedal. (Most systems will prevent the vehicle accelerating beyond the chosen speed, but will not apply the brakes in the event of overspeeding downhill.)  On vehicles with a manual transmission, cruise control is less flexible because the act of depressing the clutch pedal and shifting gears usually disengages the cruise control. The "resume" feature has to be used each time after selecting the new gear and releasing the clutch. Therefore, cruise control is of most benefit at motorway/highway speeds when top gear is used virtually all the time.

Advantages and disadvantages.

Some advantages of cruise control include:  However, when used incorrectly cruise control can lead to accidents due to several factors, such as:

Adaptive cruise control.

Some modern vehicles have systems for adaptive cruise control (ACC), which is a general term meaning improved cruise control. These improvements can be automatic braking or dynamic set-speed type controls.  Automatic Braking Type: the automatic braking type use either a single or combination of sensors (radar, lidar, and camera) to allow the vehicle to keep pace with the car it is following, slow when closing in on the vehicle in front and accelerating again to the preset speed when traffic allows. Some systems also feature forward collision warning systems, which warn the driver if a vehicle in front—given the speed of both vehicles—gets too close (within the preset headway or braking distance).  Dynamic Set Speed Type: The dynamic set speed uses the GPS position of speed limit signs, from a database. Some are modifiable by the driver.  Non-Braking Type: The speed can be adjusted to allow traffic calming.  Dynamic radar cruise control: uses a camera and millimeter-wave radar to maintain a set point distance from vehicles in front of the car; the system will automatically slow down or speed up based on the vehicles in front.  Vehicles with adaptive cruise control are considered a Level 1 autonomous car, as defined by SAE International.

See also.

PID controller - Fundamental control concept used in car cruise control

Cruise control (sometimes known as speed control or autocruise, or tempomat in some countries) is a system that automatically controls the speed of a motor vehicle. The system is a servomechanism that takes over the throttle of the car to maintain a steady speed as set by the driver.

巡航定速(英语:英语:Cruise Control),是安装在汽车中能够自动控制车辆行驶速度的装置。巡航定速有时也被厂家称为定速巡航、速度控制(英语:英语:Speed Control)或自动巡航(英语:英语:Autocruise)。


History.

Early times.

Indre-et-Loire is one of the original 83 departments established during the French Revolution on 4 March 1790. It was created from the former province of Touraine and of small portions of Orléanais, Anjou and Poitou.. Its prefecture Tours was a centre of learning in the Early Middle Ages, having been a key focus of Christian evangelisation since St Martin became its first bishop around 375. From the mid-15th century, the royal court repaired to the Loire Valley, with Tours as its capital; the confluence of the Loire River and Cher River became a centre of silk manufacturing and other luxury goods, including the wine trade, creating a prosperous bourgeoisie.

Recent years.

After the creation of the department it remained politically conservative, as Honoré de Balzac recorded in several of his novels. Conservative Tours refused to welcome the railways which instead were obliged to route their lines by way of Saint-Pierre-des-Corps on the city's eastern edge. The moderate temper of the department's politics remained apparent after the Franco-Prussian War of 1870: sentiments remained predominantly pro-royalist during the early years of the Third Republic. For most of the nineteenth century, Indre-et-Loire was a rural department, but pockets of heavy-duty industrialisation began to appear towards the century's end, accompanied by left-wing politics. 1920 saw the birth of the French Communist Party at the Congress of Tours. By 1920, Saint-Pierre-des-Corps had become a major railway hub and a centre of railway workshops: it had also acquired a reputation as a bastion of working class solidarity.

Geography.

Indre-et-Loire is part of the region of Centre-Val de Loire; it is surrounded by the departments of Loir-et-Cher, Indre, Vienne, Maine-et-Loire and Sarthe.

Politics.

The President of the General Council is Marisol Touraine of the Socialist Party.

Tourism.

Indre-et-Loire is home to numerous outstanding châteaux that are open to the public, among them are the following:

Indre-et-Loire () is a department in west-central France named after the Indre River and Loire River. In 2016, it had a population of 606,223. Sometimes referred to as Touraine, the name of the historic region, it nowadays is part of the Centre-Val de Loire region. Its prefecture is Tours and subprefectures are Chinon and Loches. Indre-et-Loire is a touristic destination for its numerous monuments that are part of the Châteaux of the Loire Valley.

安德尔-卢瓦尔省(法文:)是法国中央-卢瓦尔河谷大区所辖的省份。该省编号为37。它是以安德尔河和卢瓦尔河这两条河流命名的。它位于法国中部,它包括法国历史上的图尔地区。


History.

From the Middle Ages to the Enlightenment.

The University was founded on 12 March 1365 by Rudolf IV, Duke of Austria, and his two brothers, Dukes Albert III and Leopold III, hence the additional name "Alma Mater Rudolphina". After the Charles University in Prague and Jagiellonian University in Kraków, the University of Vienna is the third oldest university in Central Europe and the oldest university in the contemporary German-speaking world; it remains a question of definition as the Charles University in Prague was German-speaking when founded, too.  The University of Vienna was modelled after the University of Paris. However, Pope Urban V did not ratify the deed of foundation that had been sanctioned by Rudolf IV, specifically in relation to the department of theology. This was presumably due to pressure exerted by Charles IV, Holy Roman Emperor, who wished to avoid competition for the Charles University in Prague. Approval was finally received from the Pope in 1384 and the University of Vienna was granted the status of a full university, including the Faculty of Catholic Theology. The first university building opened in 1385. It grew into the biggest university of the Holy Roman Empire, and during the advent of Humanism in the mid-15th century was home to more than 6,000 students.  In its early years, the university had a partly hierarchical, partly cooperative structure, in which the Rector was at the top, while the students had little say and were settled at the bottom. The Magister and Doctors constituted the four faculties and elected the academic officials from amidst their ranks. The students, but also all other Supposita (university members), were divided into four Academic Nations. Their elected board members, mostly graduates themselves, had the right to elect the Rector. He presided over the Consistory which included procurators of each of the nations and the faculty deans, as well as over the University Assembly, in which all university teachers participated. Complaints or appeals against decisions of faculty by the students had to be brought forward by a Magister or Doctor.  Being considered a Papal Institution, the university suffered quite a setback during the Reformation. In addition, the first Siege of Vienna by Ottoman forces had devastating effects on the city, leading to a sharp decline, with only 30 students enrolled at the lowest point. For King Ferdinand I, this meant that the university should be tied to the church to an even stronger degree, and in 1551 he installed the Jesuit Order there. With the enacting of the "Sanctio Pragmatica" edict by emperor Ferdinand II in 1623, the Jesuits took over teaching at the theological and philosophical faculty, and thus the university became a stronghold of Catholicism for over 150 years. It was only in the Mid-18th century that Empress Maria Theresa forced the university back under control of the monarchy. Her successor Joseph II helped in the further reform of the university, allowing both Protestants and Jews to enroll as well as introducing German as the compulsory language of instruction.

From the 19th century onwards.

Big changes were instituted in the wake of the Revolution in 1848, with the Philosophical Faculty being upgraded into equal status as Theology, Law and Medicine. Led by the reforms of Leopold, Count von Thun und Hohenstein, the university was able to achieve a larger degree of academic freedom. The current main building on the Ringstraße was built between 1877 and 1884 by Heinrich von Ferstel. The previous main building was located close to the "Stuben" Gate (Stubentor) on Iganz Seipel Square, current home of the old University Church ("Universitätskirche") and the Austrian Academy of Sciences ("Österreichische Akademie der Wissenschaften"). Women were admitted as full students from 1897, although their studies were limited to Philosophy. The remaining departments gradually followed suit, although with considerable delay: Medicine in 1900, Law in 1919, Protestant Theology in 1923 and finally Roman Catholic Theology in 1946. Ten years after the admission of the first female students, Elise Richter became the first woman to receive "habilitation", becoming professor of Romance Languages in 1907; she was also the first female distinguished professor.  In the late 1920s, the university was in steady turmoil because of anti-democratic and anti-Semitic activity by parts of the student body. Professor Moritz Schlick was killed by a former student while ascending the steps of the University for a class. His murderer was later released by the Nazi Regime. Following the Anschluss, the annexation of Austria into Greater Germany by the Nazi regime, in 1938 the University of Vienna was reformed under political aspects and a huge number of teachers and students were dismissed for political and "racial" reasons. In April 1945, the then 22-year-old Kurt Schubert, later acknowledged doyen of Judaic Studies at the University of Vienna, was permitted by the Soviet occupation forces to open the university again for teaching, which is why he is regarded as the unofficial first rector in the post-war period. On 25 April 1945, however, the constitutional lawyer Ludwig Adamovich senior was elected as official rector of the University of Vienna. A large degree of participation by students and university staff was realized in 1975, however the University Reforms of 1993 and 2002 largely re-established the professors as the main decision makers. However, also as part of the last reform, the university after more than 250 years being largely under governmental control, finally regained its full legal capacity. The number of faculties and centers was increased to 18, and the whole of the medical faculty separated into the new Medical University of Vienna.

Location.

The University of Vienna does not have one single campus. Historically, the university started functioning from the First District near the Jesuit Church. Now, the academic facilities occupy more than sixty locations throughout the city of Vienna. The historical main building on the Ringstraße constitutes the university's centre and is commonly referred to as "die Uni". Most other larger university facilities and lecture halls are located nearby in the area of Vienna's First and Ninth District: the so-called new Lecture Hall Complex (Neues Institutgebäude, NIG), the lecture hall complex Althanstraße (UZA), the campus on the premises of the Historical General Hospital of Vienna, the Faculty of Law (Juridicum) and others. The Botanical Garden of the University of Vienna is housed in the Third District, as are the Department of Biochemistry and related research centres.  Also worth mentioning is the Vienna Observatory, which belongs to the university, and the Institute for University Sports (USI), which offers training and recreational possibilities to all students of the university.  In addition, the University of Vienna maintains facilities outside of Vienna in the Austrian provinces of Lower Austria, Upper Austria and Salzburg. These are mainly research and experimental departments for Biology, Astrophysics and Sports.

Organization.

The University of Vienna, like all universities and academies in Austria, once featured a system of democratic representation. Power in the university was divided equally among three groups: students (the largest group), junior faculty and full professors. All groups had the right to send representatives to boards, who then voted on almost every issue. From 2002 on, the government of Austria, headed by chancellor Wolfgang Schüssel, reformed the university system, transforming the institutions into legal entities, but also concentrating power in the hands of the full professors. The reform also introduced a board of governors and tuition fees. In 2013 those amounted to about €381 per semester for students from Austria, the European Union as well as some non-EU countries, while students from developed non-EU countries usually pay double that amount. The reforms also separated the medical departments into separate medical schools, such as the Medical University of Vienna.

Programmes.

Students at the university can select from 181 degree programmes: 55 bachelor programmes, 110 master programmes, 3 diploma programs and 13 doctoral programmes. In the academic year 2013/14, the university awarded 7,745 first degrees (Bachelors and Diplomas), 1,424 Master's degrees and 568 Doctoral degrees. The university offers a number of Masters programs in English, namely:  Some 6,900 scholars undertake the research and teaching activity of the university. Of these, approximately 1,000 engage actively in projects financed by third parties. The main fields of research at the university cover a wide spectrum of subjects: Catholic and Protestant Theology, Law, Economic Sciences and Computer Science, Philological-Cultural Studies and Historical-Cultural Studies, Social Sciences and Psychology, Life Sciences and Natural Sciences, Mathematics, Sports Sciences and Teacher Education.

Faculties and centres.

The University of Vienna consists of 15 faculties and four centres:

Famous members.

Faculty and scholars.

Nobel Prize Laureates who taught at the University of Vienna include Robert Bárány, Julius Wagner-Jauregg, Hans Fischer, Karl Landsteiner, Erwin Schrödinger, Victor Franz Hess, Otto Loewi, Konrad Lorenz and Friedrich Hayek.  The University of Vienna was the cradle of the Austrian School of economics. The founders of this school who studied and later instructed at the University of Vienna included Carl Menger, Eugen von Böhm-Bawerk, Friedrich von Wieser, Joseph Schumpeter, Ludwig von Mises and Friedrich Hayek.  Other famous scholars who have taught at the University of Vienna are: Theodor W. Adorno, Alexander Van der Bellen, Manfred Bietak, Theodor Billroth, Ludwig Boltzmann, Ulrich Brand, Franz Brentano, Anton Bruckner, Rudolf Carnap, Conrad Celtes, Viktor Frankl, Sigmund Freud, Eduard Hanslick, Edmund Hauler, Leon Kellner, Hans Kelsen, Adam František Kollár, Johann Josef Loschmidt, Franz Miklosich, Oskar Morgenstern, Otto Neurath, Johann Palisa, Pope Pius II, Elise Richter, Baron Carl von Rokitansky, Rudolf von Scherer, August Schleicher, Moritz Schlick, Ludwig Karl Schmarda, Joseph von Sonnenfels, Josef Stefan, Olga Taussky-Todd, Walter G. Url, Leopold Vietoris, Jalile Jalil, Carl Auer von Welsbach, and Wilhelm Winkler.

Alumni.

Some of the University's better-known students include: Kurt Adler, Franz Alt, Wilhelm Altar, Maria Anwander, Bruno Bettelheim, Rudolf Bing, Lucian Blaga, Hedda Bolgar, Josef Breuer, F. F. Bruce, Elias Canetti, Ivan Cankar, Otto Maria Carpeaux, Christian Doppler, Felix Ehrenhaft, Mihai Eminescu, Stephen Ferguson Paul Feyerabend, Heinz Fischer, O. W. Fischer, Ivan Franko, Sigmund Freud, Alcide De Gasperi, Kurt Gödel, Ernst Gombrich, Erich Göstl, Franz Grillparzer, Werner Gruber, Jörg Haider, Hans Hahn, Theodor Herzl, Hugo von Hofmannsthal, Edmund Husserl, Marie Jahoda, Max Jammer, Elfriede Jelinek, Percy Lavon Julian, Percy Julian, Karl Kautsky, Elisabeth Kehrer, Leon Kellner, Hans Kelsen, Hryhoriy Khomyshyn, Jan Kickert, Rudolf Kirchschläger, Arthur Koestler, Jernej Kopitar, Karl Kordesch, Arnold Krammer, Karl Kraus, Bruno Kreisky, Richard Kuhn, Paul Lazarsfeld, Ignacy Łukasiewicz, Gustav Mahler, Tomáš Garrigue Masaryk, Lise Meitner, Gregor Mendel, Karl Menger, Franz Mesmer, Franz Miklosich, Alois Mock, Wolf-Dieter Montag, Matija Murko, Joachim Oppenheim, Eduard Pernkopf, Anton Piëch, Pope Pius III, Maxim Podoprigora, Hans Popper, Karl Popper, Otto Preminger, Wilhelm Reich, Peter Safar, Mordkhe Schaechter, Karl Schenkl, Arthur Schnitzler, Albin Schram, Joseph Schumpeter, Wolfgang Schüssel, John J. Shea, Jr., Felix Somary, Adalbert Stifter, Countess Stoeffel, Yemima Tchernovitz-Avidar, Eric Voegelin, Kurt Waldheim, Otto Weininger, Slavko Wolf, Eduard Zirm, Mordecai Sandberg, Sandra Wachter, Calvin Edouard Ward, Paul Niel, Stefan Zweig, and Huldrych Zwingli.

Nobel Prize Laureates.

There are total 15 Nobel Prize Laureates affiliated to the University as follows:

The University Library.

The University Library of the University of Vienna comprises the Main Library and the 50 departmental libraries at the various university locations throughout Vienna. The library's primary responsibility is to the members of the university; however, the library's 350 staff members also provide access to the public. Use of the books in the reading halls is open to all persons without the need for identification, which is only required for checking out books. The library's website provides direct access to information such as electronic journals, online indices and databases.

Library history.

Rudolf IV had already provided for a "publica libraria" in the Foundation Deed of 12 March 1365, where the valuable books bequeathed by deceased members of the University should be collected. Through many legacies, this collection was subsequently greatly increased and became the basis of the old "Libreye" that was accommodated in the same building as the student infirmary. In addition, there were libraries in the separate Faculties and in the Duke's College.  From the 17th century onwards, interest in the old library, with its manuscripts and incunabulae, went into decline and the modern library in the Jesuit College came to the fore. In 1756, the oldest university library was finally closed down and its books, 2,787 volumes, were incorporated into the Court Library, of which Gerard van Swieten was then director. After the dissolution of the Jesuit order (1773), the new "Academic Library" was created out of the book collections of the five Lower Austrian Colleges and many duplicates from the Court Library. This was opened on 13 May 1777, the birthday of Maria Theresa of Austria, in the building of the Academic College. Initially, the stock consisted of some 45,000 books and during Emperor Joseph II's dissolution of the monasteries, this was soon considerably extended. In contrast to its antecedents, the new library was open to the general public. Between 1827 and 1829, it acquired the classicist extension (Postgasse 9) to the Academic College, in which it was to be accommodated until 1884. In this year, the main library, with some 300,000 books, moved to Heinrich von Ferstel's new Main Building on the Ring, where stacks for some 500,000 volumes had already been prepared. With an annual growth of up to 30,000 volumes, the surplus space was soon filled. Book storage space had to be extended continuously. One hundred years later, the complete library, including departmental and subject libraries, comprised more than 4.3 million volumes. Today, Vienna's University Library is the largest collection of books in Austria, still facing problems of space. In addition to the Main Library, which alone has to cope with an annual growth of 40,000 volumes, it includes three Faculty Libraries, 32 Subject Libraries and 26 Departmental Libraries.  "Data as of 2014"

International acclaim.

The University of Vienna has the highest ranking in Arts and Humanities, where it is placed 35 and 54th in the world according to the THE and QS ranking respectively. Outstanding subjects include Geography (ranked 28th globally in 2013), Linguistics and Philosophy (both 46th globally) and Law (ranked 32nd in Europe and 73rd globally). It is rated high in academic reputation and number of international students, but low in terms of faculty to student ratio and citations per faculty.  An overview of the QS World University Rankings by subjects:  The Times Higher Education World University Rankings by subjects:

The University of Vienna () is a public university located in Vienna, Austria. It was founded by Duke Rudolph IV in 1365 and is the oldest university in the German-speaking world. With its long and rich history, the University of Vienna has developed into one of the largest universities in Europe, and also one of the most renowned, especially in the Humanities. It is associated with 20 Nobel prize winners and has been the academic home to many scholars of historical as well as of academic importance.

维也纳大学()位于奥地利首都维也纳,始建于1365年,是现存最古老的德语大学之一,也是中欧最大的学校之一,维也纳大学亦是目前最大的德语大学,学校共设有180个学位。在奥地利,维也纳大学的也是最大的教学和研究机构,拥有近8,600名员工,其中有6,500名学者。截止2017年,共有20位校友及教职工曾获得诺贝尔奖。


Signs and symptoms.

Floaters are from objects in pockets of liquid within the vitreous humour, the thick fluid or gel that fills the eye. or between the vitreous and the retina. The vitreous humour, or vitreous body, is a jelly-like, transparent substance that fills the majority of the eye. It lies within the vitreous chamber behind the lens, and is one of the four optical components of the eye. Thus, floaters follow the rapid motions of the eye, while drifting slowly within the pocket of liquid. When they are first noticed, the natural reaction is to attempt to look directly at them. However, attempting to shift one's gaze toward them can be difficult because floaters follow the motion of the eye, remaining to the side of the direction of gaze. Floaters are, in fact, visible only because they do not remain perfectly fixed within the eye. Although the blood vessels of the eye also obstruct light, they are invisible under normal circumstances because they are fixed in location relative to the retina, and the brain "tunes out" stabilized images through neural adaptation.  Floaters are particularly noticeable when looking at a blank surface or an open monochromatic space, such as blue sky. Despite the name "floaters", many of these specks have a tendency to sink toward the bottom of the eyeball, in whichever way the eyeball is oriented; the supine position (looking up or lying back) tends to concentrate them near the fovea, which is the center of gaze, while the textureless and evenly lit sky forms an ideal background against which to view them. The brightness of the daytime sky also causes the eyes' pupils to contract, reducing the aperture, which makes floaters less blurry and easier to see.  Floaters present at birth usually remain lifelong, while those that appear later may disappear within weeks or months. They are not uncommon, and do not cause serious problems for most persons; they represent one of the most common presentations to hospital eye services. A survey of optometrists in 2002 suggested that an average of 14 patients per month per optometrist presented with symptoms of floaters in the UK. However, floaters are more than a nuisance and a distraction to those with severe cases, especially if the spots seem constantly to drift through the field of vision. The shapes are shadows projected onto the retina by tiny structures of protein or other cell debris discarded over the years and trapped in the vitreous humour or between the vitreous and retina. Floaters can even be seen when the eyes are closed on especially bright days, when sufficient light penetrates the eyelids to cast the shadows. It is not, however, only elderly persons who are troubled by floaters; they can also become a problem to younger people, especially if they are myopic. They are also common after cataract operations or after trauma.  Floaters are able to catch and refract light in ways that somewhat blur vision temporarily until the floater moves to a different area. Often they trick persons who are troubled by floaters into thinking they see something out of the corner of their eye that really is not there. Most persons come to terms with the problem, after a time, and learn to ignore their floaters. For persons with severe floaters it is nearly impossible to ignore completely the large masses that constantly stay within almost direct view.

Causes.

There are various causes for the appearance of floaters, of which the most common are described here.  Floaters can occur when eyes age; in rare cases, floaters may be a sign of retinal detachment or a retinal tear.

Vitreous syneresis.

The cause of a vitreous floater is due to vitreous syneresis (liquefaction) and contraction with age. Additionally, trauma or injury to the globe can cause vitreous floaters.

Vitreous detachments and retinal detachments.

In time, the liquefied vitreous body loses support and its framework contracts. This leads to posterior vitreous detachment, in which the vitreous membrane is released from the sensory retina. During this detachment, the shrinking vitreous can stimulate the retina mechanically, causing the patient to see random flashes across the visual field, sometimes referred to as "flashers", a symptom more formally referred to as photopsia. The ultimate release of the vitreous around the optic nerve head sometimes makes a large floater appear, usually in the shape of a ring ("Weiss ring"). As a complication, part of the retina might be torn off by the departing vitreous membrane, in a process known as retinal detachment. This will often leak blood into the vitreous, which is seen by the patient as a sudden appearance of numerous small dots, moving across the whole field of vision. Retinal detachment requires immediate medical attention, as it can easily cause blindness. Consequently, both the appearance of flashes and the sudden onset of numerous small floaters should be rapidly investigated by an eye care provider.  Posterior vitreous detachment is more common in people who:

Regression of the hyaloid artery.

The hyaloid artery, an artery running through the vitreous humour during the fetal stage of development, regresses in the third trimester of pregnancy. Its disintegration can sometimes leave cell matter.

Other common causes.

Patients with retinal tears may experience floaters if red blood cells are released from leaky blood vessels, and those with uveitis or vitritis, as in toxoplasmosis, may experience multiple floaters and decreased vision due to the accumulation of white blood cells in the vitreous humour.  Other causes for floaters include cystoid macular edema and asteroid hyalosis. The latter is an anomaly of the vitreous humour, whereby calcium clumps attach themselves to the collagen network. The bodies that are formed in this way move slightly with eye movement, but then return to their fixed position.

Diagnosis.

Floaters are often readily observed by an ophthalmologist or an optometrist with the use of an ophthalmoscope or slit lamp. However, if the floater is near the retina, it may not be visible to the observer even if it appears large to the patient.  Increasing background illumination or using a pinhole to effectively decrease pupil diameter may allow a person to obtain a better view of his or her own floaters. The head may be tilted in such a way that one of the floaters drifts towards the central axis of the eye. In the sharpened image the fibrous elements are more conspicuous.  The presence of retinal tears with new onset of floaters was surprisingly high (14%; 95% confidence interval, 12–16%) as reported in a meta-analysis published as part of the Rational Clinical Examination Series in the Journal of the American Medical Association. Patients with new onset flashes and/or floaters, especially when associated with visual loss or restriction in the visual field, should seek more urgent ophthalmologic evaluation.

Treatment.

While surgeries do exist to correct for severe cases of floaters, there are no medications (including eye drops) that can correct for this vitreous deterioration. Floaters are often caused by the normal aging process and will usually become less bothersome as a person learns to ignore them. Looking up/down and left/right will cause the floaters to leave the direct field of vision as the vitreous humour swirls around due to the sudden movement. If floaters significantly increase in numbers and/or severely affect vision, then one of the below treatments may be necessary. , insufficient evidence is available to compare the safety and efficacy of surgical vitrectomy with laser vitreolysis for the treatment of floaters. A 2017 Cochrane Review did not find any relevant studies that compared the two treatments.  Aggressive marketing campaigns have promoted the use of laser vitreolysis for the treatment of floaters. No strong evidence currently exists for the treatment of floaters with laser vitreolysis. The strongest available evidence comparing these two treatment modalities are retrospective case series.

Surgery.

Vitrectomy may be successful in treating more severe cases. The technique usually involves making three openings through the part of the sclera known as the pars plana. Of these small gauge instruments, one is an infusion port to resupply a saline solution and maintain the pressure of the eye, the second is a fiber optic light source, and the third is a vitrector. The vitrector has a reciprocating cutting tip attached to a suction device. This design reduces traction on the retina via the vitreous material. A variant sutureless, self-sealing technique is sometimes used.  Like most invasive surgical procedures, however, vitrectomy carries a risk of complications, including: retinal detachment, anterior vitreous detachment and macular edema – which can threaten vision or worsen existing floaters (in the case of retinal detachment).

Laser.

Laser vitreolysis is a possible treatment option for the removal of vitreous strands and opacities (floaters). In this procedure an ophthalmic laser (usually a yttrium aluminium garnet (YAG) laser) applies a series of nanosecond pulses of low-energy laser light to evaporate the vitreous opacities and to sever the vitreous strands. When performed with a YAG laser designed specifically for vitreolysis, reported side effects and complications associated with vitreolysis are rare. However, YAG lasers have traditionally been designed for use in the anterior portion of the eye, i.e. posterior capsulotomy and iridotomy treatments. As a result, they often provide a limited view of the vitreous, which can make it difficult to identify the targeted floaters and membranes. They also carry a high risk of damage to surrounding ocular tissue. Accordingly, vitreolysis is not widely practised, being performed by very few specialists. One of them, John Karickhoff, has performed the procedure more than 1,400 times and claims a 90 percent success rate. However, the MedicineNet web site states that "there is no evidence that this [laser treatment] is effective. The use of a laser also poses significant risks to the vision in what is otherwise a healthy eye."

Medication.

Enzymatic vitreolysis has been trialed to treat vitreomacular adhesion (VMA) and anomalous posterior vitreous detachment. Although the mechanism of action may have an effect on clinically significant floaters, there are no clinical trials being undertaken to determine whether this may be a therapeutic alternative to either conservative management, or vitrectomy.

Epidemiology.

A vitreous detachment typically affects patients older than the age of 50 and increases in prevalence by age 80. Individuals who are myopic or nearsighted have an increased risk of vitreous floaters. Additionally, eyes with an inflammatory disease after direct trauma to the globe or have recently undergone eye surgery have an increased chance of developing a vitreous floater. Men and women appear to be affected equally.

Floaters are sometimes visible deposits within the eye's vitreous humour ("the vitreous"), which is normally transparent, or between the vitreous and retina. Each floater can be measured by its size, shape, consistency, refractive index, and motility. They are also called "muscae volitantes" (Latin for 'flying flies'), or "mouches volantes" (from the French). The vitreous usually starts out transparent, but imperfections may gradually develop as one ages. The common type of floater, present in most people's eyes, is due to these degenerative changes of the vitreous. The perception of floaters, which may be annoying or problematic to some people, is known as myodesopsia, or, less commonly, as "myodaeopsia", "myiodeopsia", or "myiodesopsia". It is not often treated, except in severe cases, where vitrectomy (surgery), laser vitreolysis, and medication may be effective.

飞蚊症正式名称为玻璃体混沌或玻璃体浮游物,又称云雾移睛。是一种因投入眼睛的光线将浮游在玻璃体的混浊物投影在视网膜上,而在视野中看到物体漂浮的现象。这些玻璃体浮游物在玻璃体中具有不同大小、形状、浓稠度、折射率和能动性,并且通常都是以透明的型态呈现。当人还在年轻的时候,玻璃体是透明的,但是当人开始老化时,玻璃体就会逐渐混浊,而一般存在于人体眼中的浮游物就是因为玻璃体的退化变性所造成的。当光线将这些玻璃体浮游物投影在视网膜上就会被人眼所看见。人眼中通常可以看见的浮游物会在视野中单独出现或者是与其他的浮游物一同出现,这些物体可以是点状、条状、网状,一个或数个一起出现,并在患者的眼睛中漂浮,所以飞蚊症不属于视觉假象而是属于内视现象。而这些物体因为是漂浮在玻璃体当中,随着眼球的转动而移动,如同蚊子在眼前飞舞,故称为「飞蚊症」。


Summary.

The dialogue is told from the perspective of one of Socrates' students, Phaedo of Elis, who was present at Socrates' death bed. Phaedo relates the dialogue from that day to Echecrates, a Pythagorean philosopher.  Socrates offers four arguments for the soul's immortality:

Introductory conversation.

The scene is set in Phlius where Echecrates who, meeting Phaedo, asks for news about the last days of Socrates. Phaedo explains why a delay occurred between his trial and his death, and describes the scene in a prison at Athens on the final day, naming those present. He tells how he had visited Socrates early in the morning with the others. Socrates' wife Xanthippe was there, but was very distressed and Socrates asked that she be taken away. Socrates' relates how, bidden by a recurring dream to "make and cultivate music", he wrote a hymn and then began writing poetry based on Aesop's Fables.  Socrates tells Cebes to "bid him (his friend) farewell from me; say that I would have him come after me if he be a wise man" Simmias expresses confusion as to why they ought hasten to follow Socrates to death. Socrates then states "... he, who has the spirit of philosophy, will be willing to die; but he will not take his own life." Cebes raises his doubts as to why suicide is prohibited. He asks, "Why do you say... that a man ought not to take his own life, but that the philosopher will be ready to follow one who is dying?" Socrates replies that while death is the ideal home of the soul, man, specifically the philosopher, should not commit suicide except when it becomes necessary.  Man ought not to kill himself because he possesses no actual ownership of himself, as he is actually the property of the gods. He says, "I too believe that the gods are our guardians, and that we men are a chattel of theirs". While the philosopher seeks always to rid himself of the body, and to focus solely on things concerning the soul, to commit suicide is prohibited as man is not sole possessor of his body. For, as stated in the "Phaedo": "the philosopher more than other men frees the soul from association with the body as much as possible". Body and soul are separate, then. The philosopher frees himself from the body because the body is an impediment to the attainment of truth.  Of the senses' failings, Socrates says to Simmias in the "Phaedo": Did you ever reach them (truths) with any bodily sense? – and I speak not of these alone, but of absolute greatness, and health, and strength, and, in short, of the reality or true nature of everything. Is the truth of them ever perceived through the bodily organs? Or rather, is not the nearest approach to the knowledge of their several natures made by him who so orders his intellectual vision as to have the most exact conception of the essence of each thing he considers?  The philosopher, if he loves true wisdom and not the passions and appetites of the body, accepts that he can come closest to true knowledge and wisdom in death, as he is no longer confused by the body and the senses. In life, the rational and intelligent functions of the soul are restricted by bodily senses of pleasure, pain, sight, and sound. Death, however, is a rite of purification from the "infection" of the body. As the philosopher practices death his entire life, he should greet it amicably and not be discouraged upon its arrival, for, since the universe the Gods created for us in life is essentially "good," why would death be anything but a continuation of this goodness? Death is a place where better and wiser Gods rule and where the most noble souls exist: "And therefore, so far as that is concerned, I not only do not grieve, but I have great hopes that there is something in store for the dead..., something better for the good than for the wicked."  The soul attains virtue when it is purified from the body: "He who has got rid, as far as he can, of eyes and ears and, so to speak, of the whole body, these being in his opinion distracting elements when they associate with the soul hinder her from acquiring truth and knowledge – who, if not he, is likely to attain to the knowledge of true being?"

The Cyclical Argument.

Cebes voices his fear of death to Socrates: "... they fear that when she [the soul] has left the body her place may be nowhere, and that on the very day of death she may perish and come to an end immediately on her release from the body... dispersing and vanishing away into nothingness in her flight."  In order to alleviate Cebes' worry that the soul might perish at death, Socrates introduces his first argument for the immortality of the soul. This argument is often called the "Cyclical Argument". It supposes that the soul must be immortal since the living come from the dead. Socrates says: "Now if it be true that the living come from the dead, then our souls must exist in the other world, for if not, how could they have been born again?". He goes on to show, using examples of relationships, such as asleep-awake and hot-cold, that things that have opposites come to be from their opposite. One falls asleep after having been awake. And after being asleep, he awakens. Things that are hot came from being cold and vice versa. Socrates then gets Cebes to conclude that the dead are generated from the living, through death, and that the living are generated from the dead, through birth. The souls of the dead must exist in some place for them to be able to return to life.

The Theory of Recollection Argument.

Cebes realizes the relationship between the "Cyclical Argument" and Socrates' "Theory of Recollection". He interrupts Socrates to point this out, saying: ... your favorite doctrine, Socrates, that our learning is simply recollection, if true, also necessarily implies a previous time in which we have learned that which we now recollect. But this would be impossible unless our soul had been somewhere before existing in this form of man; here then is another proof of the soul's immortality.  Socrates' second argument, the "Theory of Recollection", shows that it is possible to draw information out of a person who seems not to have any knowledge of a subject prior to his being questioned about it (a priori knowledge). This person must have gained this knowledge in a prior life, and is now merely recalling it from memory. Since the person in Socrates' story is able to provide correct answers to his interrogator, it must be the case that his answers arose from recollections of knowledge gained during a previous life.

The Affinity Argument.

Socrates presents his third argument for the immortality of the soul, the so-called "Affinity Argument", where he shows that the soul most resembles that which is invisible and divine, and the body resembles that which is visible and mortal. From this, it is concluded that while the body may be seen to exist after death in the form of a corpse, as the body is mortal and the soul is divine, the soul must outlast the body.  As to be truly virtuous during life is the quality of a great man who will perpetually dwell as a soul in the underworld. However, regarding those who were not virtuous during life, and so favored the body and pleasures pertaining exclusively to it, Socrates also speaks. He says that such a soul as this is: ... polluted, is impure at the time of her departure, and is the companion and servant of the body always and is in love with and bewitched by the body and by the desires and pleasures of the body, until she is led to believe that the truth only exists in a bodily form, which a man may touch and see, and drink and eat, and use for the purposes of his lusts, the soul, I mean, accustomed to hate and fear and avoid that which to the bodily eye is dark and invisible, but is the object of mind and can be attained by philosophy; do you suppose that such a soul will depart pure and unalloyed?  Persons of such a constitution will be dragged back into corporeal life, according to Socrates. These persons will even be punished while in Hades. Their punishment will be of their own doing, as they will be unable to enjoy the singular existence of the soul in death because of their constant craving for the body. These souls are finally "imprisoned in another body". Socrates concludes that the soul of the virtuous man is immortal, and the course of its passing into the underworld is determined by the way he lived his life. The philosopher, and indeed any man similarly virtuous, in neither fearing death, nor cherishing corporeal life as something idyllic, but by loving truth and wisdom, his soul will be eternally unperturbed after the death of the body, and the afterlife will be full of goodness.  Simmias confesses that he does not wish to disturb Socrates during his final hours by unsettling his belief in the immortality of the soul, and those present are reluctant to voice their skepticism. Socrates grows aware of their doubt and assures his interlocutors that he does indeed believe in the soul's immortality, regardless of whether or not he has succeeded in showing it as yet. For this reason, he is not upset facing death and assures them that they ought to express their concerns regarding the arguments. Simmias then presents his case that the soul resembles the harmony of the lyre. It may be, then, that as the soul resembles the harmony in its being invisible and divine, once the lyre has been destroyed, the harmony too vanishes, therefore when the body dies, the soul too vanishes. Once the harmony is dissipated, we may infer that so too will the soul dissipate once the body has been broken, through death.  Socrates pauses, and asks Cebes to voice his objection as well. He says, "I am ready to admit that the existence of the soul before entering into the bodily form has been... proven; but the existence of the soul after death is in my judgment unproven." While admitting that the soul is the better part of a man, and the body the weaker, Cebes is not ready to infer that because the body may be perceived as existing after death, the soul must therefore continue to exist as well. Cebes gives the example of a weaver. When the weaver's cloak wears out, he makes a new one. However, when he dies, his more freshly woven cloaks continue to exist. Cebes continues that though the soul may outlast certain bodies, and so continue to exist after certain deaths, it may eventually grow so weak as to dissolve entirely at some point. He then concludes that the soul's immortality has yet to be shown and that we may still doubt the soul's existence after death. For, it may be that the next death is the one under which the soul ultimately collapses and exists no more. Cebes would then, "... rather not rely on the argument from superior strength to prove the continued existence of the soul after death."  Seeing that the Affinity Argument has possibly failed to show the immortality of the soul, Phaedo pauses his narration. Phaedo remarks to Echecrates that, because of this objection, those present had their "faith shaken," and that there was introduced "a confusion and uncertainty". Socrates too pauses following this objection and then warns against misology, the hatred of argument.

The Argument from Form of Life.

Socrates then proceeds to give his final proof of the immortality of the soul by showing that the soul is immortal as it is the cause of life. He begins by showing that "if there is anything beautiful other than absolute beauty it is beautiful only insofar as it partakes of absolute beauty".  Consequently, as absolute beauty is a "Form," and so is Life, then anything which has the property of being animated with Life, participates in the Form of Life. As an example he says, "will not the number three endure annihilation or anything sooner than be converted into an even number, while remaining three?". Forms, then, will never become their opposite. As the soul is that which renders the body living, and that the opposite of life is death, it so follows that, "... the soul will never admit the opposite of what she always brings." That which does not admit death is said to be immortal.  Socrates thus concludes, "Then, Cebes, beyond question, the soul is immortal and imperishable, and our souls will truly exist in another world. "Once dead, man's soul will go to Hades and be in the company of," as Socrates says, "... men departed, better than those whom I leave behind." For he will dwell amongst those who were true philosophers, like himself.

Legacy.

Plato's "Phaedo" had a significant readership throughout antiquity, and was commented on by a number of ancient philosophers, such as Harpocration of Argos, Porphyry, Iamblichus, Paterius, Plutarch of Athens, Syrianus and Proclus. The two most important commentaries on the dialogue that have come down to us from the ancient world are those by Olympiodorus of Alexandria and Damascius of Athens.  The "Phaedo" has come to be considered a seminal formulation, from which "a whole range of dualities, which have become deeply ingrained in Western philosophy, theology, and psychology over two millennia, received their classic formulation: soul and body, mind and matter, intellect and sense, reason and emotion, reality and appearance, unity and plurality, perfection and imperfection, immortal and mortal, permanence and change, eternal and temporal, divine and human, heaven and earth."

Phædo or Phaedo (;, "Phaidōn", ), also known to ancient readers as "On The Soul", is one of the best-known dialogues of Plato's middle period, along with the "Republic" and the "Symposium." The philosophical subject of the dialogue is the immortality of the soul. It is set in the last hours prior to the death of Socrates, and is Plato's fourth and last dialogue to detail the philosopher's final days, following "Euthyphro", "Apology", and "Crito".

《斐多篇》(, "Phaidōn", )是柏拉图的第四篇对话录,内容为苏格拉底饮下毒药前的对话。斐多篇当中的叙事者为斐多,一个曾受过苏格拉底帮助的年轻人并成为其弟子,在苏格拉底死亡当年亦跟随在他身旁。斐多的对话对象为弗里乌斯的伊奇,一个同是哲学家的朋友。在对话中,苏格拉底从多方面试图证明人灵魂的存在。


Overview.

Teams from 28 countries made up the joint team responsible for designing, building, flying and collecting data from the "Cassini" orbiter and "Huygens" probe.  The mission was managed by NASA's Jet Propulsion Laboratory in the United States, where the orbiter was assembled. "Huygens" was developed by the European Space Research and Technology Centre. The Centre's prime contractor, Aérospatiale of France (now Thales Alenia Space), assembled the probe with equipment and instruments supplied by many European countries ("Huygens" batteries and two scientific instruments by the United States). The Italian

Naming.

The mission consisted of two main elements: the ASI/NASA "Cassini" orbiter, named for the Italian astronomer Giovanni Domenico Cassini, discoverer of Saturn's ring divisions and four of its satellites; and the ESA-developed "Huygens" probe, named

Objectives.

"Cassini" had several objectives, including:  "Cassini–Huygens" was launched on October 15, 1997, from Cape Canaveral Air Force Station's Space Launch Complex 40 using a U.S. Air Force Titan IVB/Centaur rocket. The complete launcher was made up of a two-stage Titan IV booster rocket, two strap-on solid rocket engines, the Centaur upper stage, and a payload enclosure, or fairing.  The total cost of this scientific exploration mission was about US$3.26 billion, including $1.4 billion for pre-launch development, $704 million for mission operations, $54 million for tracking and $422 million for the launch vehicle. The United States contributed $2.6 billion (80%), the ESA $500 million (15%), and the ASI $160 million (5%). However, these figures are from

History.

"Cassini–Huygens"s origins date to 1982, when the European Science Foundation and the American National Academy of Sciences formed a working group to investigate future cooperative missions. Two European scientists suggested a paired Saturn Orbiter and Titan Probe as a possible joint mission. In 1983, NASA's Solar System Exploration Committee recommended the same Orbiter and Probe pair as a core NASA project. NASA and the European Space Agency (ESA) performed a joint study of the potential mission from 1984 to 1985. ESA continued with its own study in 1986, while the American astronaut Sally Ride, in her influential 1987 report "NASA Leadership and America's Future in Space", also examined and approved of the "Cassini" mission.  While Ride's report described the Saturn orbiter and probe as a NASA solo mission, in 1988 the Associate Administrator for Space Science and Applications of NASA, Len Fisk, returned to the idea of a joint NASA and ESA mission. He wrote to his counterpart at ESA, Roger Bonnet, strongly suggesting that ESA choose the "Cassini"

Spacecraft design.

The spacecraft was planned to be the second three-axis stabilized, RTG-powered Mariner Mark II, a class of spacecraft developed for missions beyond the orbit of Mars. "Cassini" was developed simultaneously with the "Comet Rendezvous Asteroid Flyby" ("CRAF") spacecraft, but budget cuts and project rescopings forced NASA to terminate CRAF development to save "Cassini". As a result, "Cassini" became more specialized. The Mariner Mark II series was cancelled.  The combined orbiter and probe is the third-largest unmanned interplanetary spacecraft ever successfully launched, behind the Phobos 1 and 2 Mars probes, as well as being among the most complex. The orbiter had a mass of, the probe. With the launch vehicle adapter and of propellants at launch, the spacecraft had a mass of.  The "Cassini" spacecraft was high and wide. Spacecraft complexity was increased by its trajectory (flight

Instruments.

Summary.

Description.

"Cassini"s instrumentation consisted of: a synthetic aperture radar mapper, a charge-coupled device imaging system, a visible/infrared mapping spectrometer, a composite infrared spectrometer, a cosmic dust analyzer, a radio and plasma wave experiment, a plasma spectrometer, an ultraviolet

Plutonium power source.

Because of Saturn's distance from the Sun, solar arrays were not feasible as power sources for this space probe. To generate enough power, such arrays would have been too large and too heavy. Instead, the "Cassini" orbiter was powered by three GPHS-RTG radioisotope thermoelectric generators, which use heat from the decay of about of plutonium-238 (in the form of plutonium dioxide) to generate direct current electricity via thermoelectrics. The RTGs on the "Cassini" mission have the same design as those used on the "New Horizons", "Galileo", and "Ulysses" space probes, and they were designed to have very long operational lifetimes. At the end of the nominal 11-year "Cassini" mission, they were still able to produce 600 to 700 watts of electrical power. (One of the spare RTGs for the "Cassini" mission was used to power the "New Horizons" mission to Pluto and the Kuiper belt, which was designed and launched later.)  Power distribution was accomplished by 192 solid-state power switches (SSPS), which also functioned as circuit breakers in the event of

Telemetry.

The "Cassini" spacecraft was capable of transmitting in several different telemetry formats. The telemetry subsystem is perhaps the most important subsystem, because without it there could be no data return.  The telemetry was developed from ground up, due to the spacecraft using a more modern set of computers than previous missions. Therefore, "Cassini" was the first spacecraft to adopt mini-packets to reduce the complexity of the Telemetry Dictionary, and the software

"Huygens" probe.

The "Huygens" probe, supplied by the European Space Agency (ESA) and named after the 17th century Dutch astronomer who first discovered Titan, Christiaan Huygens, scrutinized the clouds, atmosphere, and surface of Saturn's moon Titan in its descent on January 15, 2005. It was designed to enter and brake in Titan's atmosphere and parachute a fully instrumented robotic laboratory down to the surface.  The probe system consisted of the probe itself which descended to Titan, and the probe support equipment (PSE) which remained attached to the orbiting spacecraft. The PSE includes electronics that track the probe, recover the data gathered during its descent, and

Selected events and discoveries.

Venus and Earth fly-bys and the cruise to Jupiter.

The "Cassini" space probe performed two gravitational-assist flybys of Venus on April 26, 1998, and June 24, 1999. These flybys provided the space probe with enough momentum to travel all the way out to the asteroid belt. At that point, the Sun's gravity pulled the space probe back into the inner Solar System.  On August 18, 1999, at 03:28

Jupiter flyby.

"Cassini" made its closest approach to Jupiter on December 30, 2000, and made many scientific measurements. About 26,000 images of Jupiter, its faint rings, and its moons were taken during the six-month flyby. It produced the most detailed global color portrait of the planet yet (see image at right), in which the smallest visible features are approximately across. A major finding of the flyby, announced on March 6, 2003, was of Jupiter's atmospheric circulation. Dark "belts" alternate with light "zones" in the atmosphere, and scientists had long considered the zones, with their pale clouds, to be areas of upwelling air, partly because many clouds on

Tests of general relativity.

On October 10, 2003, the mission's science team announced the results of tests of Albert Einstein's general theory of relativity, performed by using radio waves transmitted from the "Cassini" space probe. The radio scientists measured a frequency shift in the radio waves to and from the spacecraft, as those passed close to the Sun. According to the general theory of relativity, a massive object like the Sun causes space-time to curve, causing a beam of

New moons of Saturn.

In total, the "Cassini" mission discovered seven new moons orbiting Saturn. Using images taken by "Cassini", researchers discovered Methone, Pallene and Polydeuces in 2004, although later analysis revealed that Voyager 2 had photographed Pallene in its 1981 flyby of the ringed planet.  On May 1, 2005, a new moon was discovered by "Cassini" in the Keeler gap. It was given the designation S/2005 S 1 before being named Daphnis. A fifth new moon was discovered by

Phoebe flyby.

On June 11, 2004, "Cassini" flew by the moon Phoebe. This was the first opportunity for close-up studies of this moon (Voyager 2 performed a distant flyby in 1981 but returned no detailed images). It also was "Cassini's" only possible flyby for Phoebe due

Saturn rotation.

In an announcement on June 28, 2004, "Cassini" program scientists described the measurement of the rotational period of Saturn. Because there are no fixed features on the surface that can be used to obtain this period, the repetition of radio emissions was used. This new data agreed with the latest values

Orbiting Saturn.

On July 1, 2004, the spacecraft flew through the gap between the F and G rings and achieved orbit, after a seven-year voyage. It was the first spacecraft to ever orbit Saturn.  The Saturn Orbital Insertion (SOI) maneuver performed by "Cassini" was complex, requiring the craft to orient its High-Gain Antenna away from Earth and along its flight path, to shield

Titan flybys.

"Cassini" had its first flyby of Saturn's largest moon, Titan, on July 2, 2004, a day after orbit insertion, when it approached to within of Titan. Images taken through special filters (able to see through the moon's global haze) showed south polar clouds thought to be composed of methane and surface features with widely differing brightness. On October 27, 2004, the spacecraft executed the first of the 45 planned close flybys of

"Huygens" lands on Titan.

"Cassini" released the "Huygens" probe on December 25, 2004, by means of a spring and spiral rails intended to rotate the probe for greater stability. It entered the atmosphere of Titan on January 14, 2005, and after

Enceladus flybys.

During the first two close flybys of the moon Enceladus in 2005, "Cassini" discovered a deflection in the local magnetic field that is characteristic for the existence of a thin but significant atmosphere. Other measurements obtained at that time point to ionized water vapor as its main constituent. "Cassini" also observed water ice geysers erupting from the south pole of Enceladus, which gives more credibility to the idea that Enceladus is supplying the particles of Saturn's E ring. Mission scientists began to suspect that there may be pockets of liquid water near the surface of the moon that fuel the eruptions.  On March 12, 2008, "Cassini" made a close fly-by of Enceladus, passing within 50 km of the moon's surface. The spacecraft passed through the plumes extending from its southern geysers, detecting water, carbon dioxide and various hydrocarbons with its mass spectrometer, while also mapping surface features that are at much higher temperature than their surroundings with

Radio occultations of Saturn's rings.

In May 2005, "Cassini" began a series of radio occultation experiments, to measure the size-distribution of particles in Saturn's rings, and measure the atmosphere of Saturn itself. For over four months, the craft completed

Spokes in rings verified.

In images captured September 5, 2005, "Cassini" detected spokes in Saturn's rings, previously seen

Lakes of Titan.

Radar images obtained on July 21, 2006 appear to show lakes of liquid hydrocarbon (such as methane and ethane) in Titan's northern latitudes. This is the first discovery of currently existing lakes anywhere besides on Earth.

Saturn hurricane.

In November 2006, scientists discovered a storm at the south pole of Saturn with a distinct eyewall. This is characteristic of a hurricane

Iapetus flyby.

On September 10, 2007, "Cassini" completed its flyby of the strange, two-toned, walnut-shaped moon, Iapetus. Images were taken from above the surface.

Mission extension.

On April 15, 2008, "Cassini" received funding for a 27-month extended mission. It consisted of 60 more orbits of Saturn, with 21 more close Titan flybys, seven

Second mission extension.

A proposal was submitted to NASA for a second mission extension (September 2010 – May 2017), provisionally named the extended-extended mission or

Great Storm of 2010 and aftermath.

On October 25, 2012, "Cassini" witnessed the aftermath of the massive Great White Spot storm that recurs roughly every 30 years on Saturn. Data from the composite infrared spectrometer (CIRS) instrument indicated a powerful discharge from the storm that caused a temperature spike in the stratosphere of Saturn above normal. Simultaneously, a huge increase in ethylene gas was detected by NASA researchers at Goddard Research Center in Greenbelt, Maryland. Ethylene is a colorless gas that is highly uncommon on Saturn and is produced both naturally

Venus transit.

On December 21, 2012, "Cassini" observed a transit of Venus across the Sun.

"The Day the Earth Smiled".

On July 19, 2013, the probe was pointed towards Earth to capture an image of the Earth and the Moon, as part of a natural light, multi-image portrait of the entire Saturn system. The event was

Rhea flyby.

On February 10, 2015, the "Cassini" spacecraft visited Rhea more closely, coming within

Hyperion flyby.

"Cassini" performed its latest flyby of Saturn's moon

Dione flyby.

"Cassini" performed its last flyby of Saturn's moon Dione on August

Hexagon changes color.

Between 2012 and 2016, the persistent hexagonal cloud pattern at Saturn's north pole changed from a mostly blue color to more of a golden color. One

Grand Finale and destruction.

"Cassini" end involved a series of close Saturn passes, approaching within the rings, then an entry into Saturn's atmosphere on September 15, 2017, to destroy the spacecraft. This method was chosen because it is imperative to ensure protection and prevent biological contamination to any of the moons of Saturn thought to offer potential habitability.  In 2008 a number of options were evaluated to achieve this goal, each with varying funding, scientific, and technical challenges. A short period Saturn impact for an end of mission was rated "excellent" with the reasons "D-ring option satisfies unachieved AO goals; cheap and easily achievable" while collision with an icy moon was rated "good" for being "cheap and achievable anywhere/time".  On November 29, 2016, the spacecraft performed a Titan flyby that took it to the gateway of F-ring orbits: This was the start of the Grand Finale phase culminating in its impact with the planet. A final Titan flyby on April 22, 2017, changed the orbit again to fly through the gap between Saturn and its inner ring days later on April 26. "Cassini" passed about above Saturn's cloud layer and from the visible edge of the inner ring; it successfully took images of Saturn's atmosphere and began returning data the next day. After a further 22 orbits through the gap, the mission was ended with a dive into Saturn's atmosphere on September 15; signal was lost at 7:55:46 AM EDT on September 15, 2017, just 30 seconds later than predicted. It is estimated that the spacecraft burned up about 45 seconds after the last transmission.  In September 2018, NASA won an Emmy Award for Outstanding Original Interactive Program for its presentation of the Cassini mission's Grand Finale at Saturn.  In January 2019, new research using data collected during Cassini's Grand Finale phase was published:

Missions.

The spacecraft operation was organized around a series of missions. Each is structured according to a certain amount of funding,

External links.

Official websites  Media and telecommunications

The Cassini–Huygens space-research mission ( ), commonly called Cassini, involved a collaboration between NASA, the European Space Agency (ESA), and the Italian Space Agency (ASI) to send a probe to study the planet Saturn and its system, including its rings and natural satellites. The Flagship-class robotic spacecraft comprised both NASA's "Cassini" probe and ESA's "Huygens" lander, which landed on Saturn's largest moon, Titan. "Cassini" was the fourth space probe to visit Saturn and the first to enter its orbit. The two craft took their names from the astronomers Giovanni Cassini and Christiaan Huygens.

卡西尼-惠更斯号()是前往土星系统的一架旗舰级太空探测器,也是由美国太空总署(NASA)、欧洲太空总署(ESA)和意大利太空总署(ASI)合作进行的任务。整个任务分为两部分:环绕土星的卡西尼号("Cassini")与在土星最大卫星土卫六登陆的惠更斯号("Huygens")。两具探测器由泰坦四号B型运载火箭搭载,于1997年10月15日一同发射升空,并于2004年7月初抵达土星轨道,随后在同年12月25日分离。卡西尼号自入轨后持续运作超过13年,直到2017年9月15日进入土星大气层焚毁;惠更斯号则于2005年1月14日成功于土卫六的阿迪立地区着陆并传回数据,是首具在外太阳系天体完成登陆的探测器。