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Leo Graetz
Leo Graetz (26 September 1856 – 12 November 1941) was a German physicist. He was born in Breslau, Germany, and was the son of historian Heinrich Graetz. Graetz was one of the first to investigate the propagation of electromagnetic energy. The Graetz number (''Gz''), a dimensionless number describing heat flow, is named after him. Also sometimes known by his name is the diode bridge rectifier circuit that was invented by Polish electrotechnician Karol Pollak in 1896 and that was independently invented and published by Leo Graetz in 1897. In 1880 he confirmed the Stefan–Boltzmann law. Graetz died in Munich Munich ( ; german: München ; bar, Minga ) is the capital and most populous city of the German state of Bavaria. With a population of 1,558,395 inhabitants as of 31 July 2020, it is the third-largest city in Germany, after Berlin and Ha ... at age 85. Publications * ''Die Elektrizität und ihre Anwendungen'' (''Electricity and Its Applications''), Stutt ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Graetz Number
In fluid dynamics, the Graetz number (Gz) is a dimensionless number that characterizes laminar flow in a conduit. The number is defined as: :\mathrm = \mathrm\, \mathrm where : ''DH'' is the diameter in round tubes or hydraulic diameter in arbitrary cross-section ducts : ''L'' is the length : Re is the Reynolds number and : Pr is the Prandtl number. This number is useful in determining the thermally developing flow entrance length in ducts. A Graetz number of approximately 1000 or less is the point at which flow would be considered thermally fully developed.Shah, R. K., and Sekulic, D. P. (2003) "Fundamentals of Heat Exchanger Design" (John Wiley and Sons), page 503. When used in connection with mass transfer the Prandtl number is replaced by the Schmidt number, Sc, which expresses the ratio of the momentum diffusivity to the mass diffusivity. :\mathrm = \mathrm\, \mathrm The quantity is named after the physicist Leo Graetz Leo Graetz (26 September 1856 – 12 Nov ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Heat Transfer
Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy (heat) between physical systems. Heat transfer is classified into various mechanisms, such as thermal conduction, Convection (heat transfer), thermal convection, thermal radiation, and transfer of energy by phase changes. Engineers also consider the transfer of mass of differing chemical species (mass transfer in the form of advection), either cold or hot, to achieve heat transfer. While these mechanisms have distinct characteristics, they often occur simultaneously in the same system. Heat conduction, also called diffusion, is the direct microscopic exchanges of kinetic energy of particles (such as molecules) or quasiparticles (such as lattice waves) through the boundary between two systems. When an object is at a different temperature from another body or its surroundings, heat flows so that the body and the surroundings reach the same temperature, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Scientists From Wrocław
A scientist is a person who conducts scientific research to advance knowledge in an area of the natural sciences. In classical antiquity, there was no real ancient analog of a modern scientist. Instead, philosophers engaged in the philosophical study of nature called natural philosophy, a precursor of natural science. Though Thales (circa 624-545 BC) was arguably the first scientist for describing how cosmic events may be seen as natural, not necessarily caused by gods,Frank N. Magill''The Ancient World: Dictionary of World Biography'', Volume 1 Routledge, 2003 it was not until the 19th century that the term ''scientist'' came into regular use after it was coined by the theologian, philosopher, and historian of science William Whewell in 1833. In modern times, many scientists have advanced degrees in an area of science and pursue careers in various sectors of the economy such as academia, industry, government, and nonprofit environments.'''' History The roles ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
People From The Province Of Silesia
A person ( : people) is a being that has certain capacities or attributes such as reason, morality, consciousness or self-consciousness, and being a part of a culturally established form of social relations such as kinship, ownership of property, or legal responsibility. The defining features of personhood and, consequently, what makes a person count as a person, differ widely among cultures and contexts. In addition to the question of personhood, of what makes a being count as a person to begin with, there are further questions about personal identity and self: both about what makes any particular person that particular person instead of another, and about what makes a person at one time the same person as they were or will be at another time despite any intervening changes. The plural form "people" is often used to refer to an entire nation or ethnic group (as in "a people"), and this was the original meaning of the word; it subsequently acquired its use as a plural form of per ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
19th-century German Physicists
The 19th (nineteenth) century began on 1 January 1801 ( MDCCCI), and ended on 31 December 1900 ( MCM). The 19th century was the ninth century of the 2nd millennium. The 19th century was characterized by vast social upheaval. Slavery was abolished in much of Europe and the Americas. The First Industrial Revolution, though it began in the late 18th century, expanding beyond its British homeland for the first time during this century, particularly remaking the economies and societies of the Low Countries, the Rhineland, Northern Italy, and the Northeastern United States. A few decades later, the Second Industrial Revolution led to ever more massive urbanization and much higher levels of productivity, profit, and prosperity, a pattern that continued into the 20th century. The Islamic gunpowder empires fell into decline and European imperialism brought much of South Asia, Southeast Asia, and almost all of Africa under colonial rule. It was also marked by the collapse of the large S ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
1941 Deaths
Events Below, the events of World War II have the "WWII" prefix. January * January–August – 10,072 men, women and children with mental and physical disabilities are asphyxiated with carbon monoxide in a gas chamber, at Hadamar Euthanasia Centre in Germany, in the first phase of mass killings under the Action T4 program here. * January 1 – Thailand's Prime Minister Plaek Phibunsongkhram decrees January 1 as the official start of the Thai solar calendar new year (thus the previous year that began April 1 had only 9 months). * January 3 – A decree (''Normalschrifterlass'') promulgated in Germany by Martin Bormann, on behalf of Adolf Hitler, requires replacement of blackletter typefaces by Antiqua. * January 4 – The short subject ''Elmer's Pet Rabbit'' is released, marking the second appearance of Bugs Bunny, and also the first to have his name on a title card. * January 5 – WWII: Battle of Bardia in Libya: Australian and British troops de ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
1856 Births
Events January–March * January 8 – Borax deposits are discovered in large quantities by John Veatch in California. * January 23 – American paddle steamer SS ''Pacific'' leaves Liverpool (England) for a transatlantic voyage on which she will be lost with all 186 on board. * January 24 – U.S. President Franklin Pierce declares the new Free-State Topeka government in "Bleeding Kansas" to be in rebellion. * January 26 – First Battle of Seattle: Marines from the suppress an indigenous uprising, in response to Governor Stevens' declaration of a "war of extermination" on Native communities. * January 29 ** The 223-mile North Carolina Railroad is completed from Goldsboro through Raleigh and Salisbury to Charlotte. ** Queen Victoria institutes the Victoria Cross as a British military decoration. * February ** The Tintic War breaks out in Utah. ** The National Dress Reform Association is founded in the United States to promote "rational" dress for ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
University And State Library Düsseldorf
The University and State Library Düsseldorf (german: Universitäts- und Landesbibliothek Düsseldorf, abbreviated ULB Düsseldorf) is a central service institution of Heinrich Heine University. Along with Bonn and Münster, it is also one of the three State Libraries of North Rhine-Westphalia. Tradition and Modernity From 1965 to 1969, the University and Library Düsseldorf gradually developed out of the Medical Academy in Düsseldorf. There is no real founding year of the ULB, but the foundation stone for an integrated library system was laid when the former State and City Library of Düsseldorf was taken over by the university in 1970 and merged with the Central Library of the former Medical Academy. Structure and Holdings The ULB consists of one central library and four decentralized locations. Management and media processing are organized centrally. Catalogues, databases, e-books and e-journals are accessible throughout the whole university as well as at home via the lib ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stefan–Boltzmann Law
The Stefan–Boltzmann law describes the power radiated from a black body in terms of its temperature. Specifically, the Stefan–Boltzmann law states that the total energy radiated per unit surface area of a black body across all wavelengths per unit time j^ (also known as the black-body ''radiant emittance'') is directly proportional to the fourth power of the black body's thermodynamic temperature ''T'': : j^ = \sigma T^. The constant of proportionality ''σ'', called the Stefan–Boltzmann constant, is derived from other known physical constants. Since 2019, the value of the constant is : \sigma=\frac = 5.670374419\times 10^\, \mathrm, where ''k'' is the Boltzmann constant, ''h'' is Planck's constant, and ''c'' is the speed of light in a vacuum. The radiance from a specified angle of view (watts per square metre per steradian) is given by : L = \frac\pi = \frac\sigma\pi T^. A body that does not absorb all incident radiation (sometimes known as a grey body) emits ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Karol Pollak
Karol Franciszek Pollak (November 15, 1859 – December 17, 1928) was a Polish electrotechnician, inventor and businessman. Early life He was born in Sanok, Kingdom of Galicia and Lodomeria, part of the Austrian Empire . His father was Karol Pollak (1818–80) who was a printer, bookseller and publisher. Karol (not to be mistaken with his father) worked in his youth as an electrician and showed great technical skills in it. In 1883 he was employed in the laboratory of British company "The Patent Utilisation Co". He designed and recorded his first patents in that period. In 1885 he attended electrotechnics studies at the Royal Polytechnic University in Charlottenburg. Activity In Berlin, Pollak ran electrotechnical factory "G. Wehr Telegraphen-Bau-Anstalt". Later he returned to Britain to commercialize his patents, which were released under anglicised version of his name, "Charles Pollak". In 1886, he became the director of a Paris company of electric tramways of his desig ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diode Bridge
A diode bridge is a bridge rectifier circuit of four diodes that is used in the process of converting alternating current (AC) from the input terminals to direct current (DC, i.e. fixed polarity) on the output terminals. Its function is to convert the negative-going AC pulses into positive going pulses, after which a low-pass filter can be used to smooth the result into DC. When used in its most common application, for conversion of an alternating-current (AC) input into a direct-current (DC) output, it is known as a bridge rectifier. A bridge rectifier provides full-wave rectification from a two-wire AC input, resulting in lower cost and weight as compared to a rectifier with a three-wire input from a transformer with a center-tapped secondary winding. The essential feature of a diode bridge is that the polarity of the output is the same regardless of the polarity at the input. The diode bridge circuit was invented by Polish electrotechnician Karol Pollak and patented ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dimensionless Number
A dimensionless quantity (also known as a bare quantity, pure quantity, or scalar quantity as well as quantity of dimension one) is a quantity to which no physical dimension is assigned, with a corresponding SI unit of measurement of one (or 1), ISBN 978-92-822-2272-0. which is not explicitly shown. Dimensionless quantities are widely used in many fields, such as mathematics, physics, chemistry, engineering, and economics. Dimensionless quantities are distinct from quantities that have associated dimensions, such as time (measured in seconds). Dimensionless units are dimensionless values that serve as units of measurement for expressing other quantities, such as radians (rad) or steradians (sr) for plane angles and solid angles, respectively. For example, optical extent is defined as having units of metres multiplied by steradians. History Quantities having dimension one, ''dimensionless quantities'', regularly occur in sciences, and are formally treated within the field of d ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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