Random Articles
Have a deep view into what people are curious about.
๐ Relativistic Quantum Chemistry
Relativistic quantum chemistry combines relativistic mechanics with quantum chemistry to explain elemental properties and structure, especially for the heavier elements of the periodic table. A prominent example of such an explanation is the color of gold: due to relativistic effects, it is not silvery like most other metals.
The term relativistic effects was developed in light of the history of quantum mechanics. Initially quantum mechanics was developed without considering the theory of relativity. Relativistic effects are those discrepancies between values calculated by models that consider and that do not consider relativity. Relativistic effects are important for the heavier elements with high atomic numbers. In the most common layout of the periodic table, these elements are shown in the lower area. Examples are the lanthanides and actinides.
Relativistic effects in chemistry can be considered to be perturbations, or small corrections, to the non-relativistic theory of chemistry, which is developed from the solutions of the Schrรถdinger equation. These corrections affect the electrons differently depending on the electron speed relative to the speed of light. Relativistic effects are more prominent in heavy elements because only in these elements do electrons attain sufficient speeds for the elements to have properties that differ from what non-relativistic chemistry predicts.
Discussed on
- "Relativistic Quantum Chemistry" | 2019-10-12 | 70 Upvotes 5 Comments
๐ HP Saturn
The Saturn family of 4-bit (datapath) microprocessors was developed by Hewlett-Packard in the 1980s first for the HP-71B handheld computer and then later for various HP calculators (starting with the HP-18C). It succeeded the Nut family of processors used in earlier calculators. The original Saturn chip was first used in the HP-71B hand-held BASIC-programmable computer, introduced in 1984. Later models of the family powered the popular HP 48 series of calculators. The HP48SX and HP48S were the last models to use genuine Saturn processors manufactured by HP. Later calculator models used Saturn processors manufactured by NEC. The HP 49 series initially used the Saturn CPU as well, until the NEC fab could no longer manufacture the processor for technical reasons in 2003. Therefore, starting with the HP 49g+ model in 2003, the calculators switched to a Samsung S3C2410 processor with an ARM920T core (part of the ARMv4T architecture) which ran an emulator of the Saturn hardware in software. In 2000, the HP 39G and HP 40G were the last calculators introduced based on the actual NEC fabricated Saturn hardware. The last calculators based on the Saturn emulator were the HP 39gs, HP 40gs and HP 50g in 2006, as well as the 2007 revision of the hp 48gII. The HP 50g, the last calculator utilizing this emulator, was discontinued in 2015 when Samsung stopped producing the ARM processor on which it was based.
Discussed on
- "HP Saturn" | 2022-09-21 | 141 Upvotes 73 Comments
๐ Staลczyk
Staลczyk (c. 1480โ1560) (Polish pronunciation:ย [หstaษฒtอกสษจk]) was a Polish court jester, the most famous in Polish history. He was employed by three Polish kings: Alexander, Sigismund the Old and Sigismund Augustus.
Discussed on
- "Staลczyk" | 2019-10-01 | 142 Upvotes 13 Comments
๐ Regional Handwriting Variation
Although people in many parts of the world share common alphabets and numeral systems (versions of the Latin writing system are used throughout the Americas, Australia, and much of Europe and Africa; the Arabic numerals are nearly universal), styles of handwritten letterforms vary between individuals, and sometimes also vary systematically between regions.
Discussed on
- "Regional Handwriting Variation" | 2023-07-01 | 35 Upvotes 22 Comments
๐ Calling card
A visiting card, also known as a calling card, is a small card used for social purposes. Before the 18th century, visitors making social calls left handwritten notes at the home of friends who were not at home. By the 1760s, the upper classes in France and Italy were leaving printed visiting cards decorated with images on one side and a blank space for hand-writing a note on the other. The style quickly spread across Europe and to the United States. As printing technology improved, elaborate color designs became increasingly popular. However, by the late 1800s, simpler styles became more common.
By the 19th century, men and women needed personalized calling or visiting cards to maintain their social status or to move up in society. These small cards, about the size of a modern-day business card, usually featured the name of the owner, and sometimes an address. Calling cards were left at homes, sent to individuals, or exchanged in person for various social purposes. Knowing and following calling card โrulesโ signaled oneโs status and intentions.
Discussed on
- "Calling card" | 2017-03-25 | 45 Upvotes 44 Comments
๐ TIL: There used to be an Internet Explorer for Unix
Internet Explorer for UNIX is a discontinued graphical web browser that was available free of charge and produced by Microsoft for use in the X Window System on Solaris or HP-UX. Development ended with a version of Internet Explorer 5 in 2001 and support for it was completely discontinued in 2002.
Discussed on
- "TIL: There used to be an Internet Explorer for Unix" | 2013-02-07 | 23 Upvotes 19 Comments
๐ B.a.t.m.a.n
The Better Approach to Mobile Ad-hoc Networking (B.A.T.M.A.N.) is a routing protocol for multi-hop mobile ad hoc networks which is under development by the German "Freifunk" community and intended to replace the Optimized Link State Routing Protocol (OLSR).
B.A.T.M.A.N.'s crucial point is the decentralization of knowledge about the best route through the networkย โ no single node has all the data. This technique eliminates the need to spread information about network changes to every node in the network. The individual node only saves information about the "direction" it received data from and sends its data accordingly. The data gets passed from node to node, and packets get individual, dynamically created routes. A network of collective intelligence is created.
In early 2007, the B.A.T.M.A.N. developers started experimenting with the idea of routing on layer 2 (Ethernet layer) instead of layer 3. To differentiate from the layer 3 routing daemon, the suffix "adv" (for: advanced) was chosen. Instead of manipulating routing tables based on information exchanged via UDP/IP, it provides a virtual network interface and transparently transports Ethernet packets on its own. The batman-adv kernel module has been part of the official Linux kernel since 2.6.38.
๐ ISO 1
ISO 1 is an international standard set by the International Organization for Standardization that specifies the standard reference temperature for geometrical product specification and verification. The temperature is fixed at 20 ยฐC, which is equal to 293.15 kelvins and 68 degrees Fahrenheit.
Due to thermal expansion, precision length measurements need to be made at (or converted to) a defined temperature. ISOย 1 helps in comparing measurements by defining such a reference temperature. The reference temperature of 20ย ยฐC was adopted by the CIPM on 15 April 1931, and became ISO recommendation number 1 in 1951. It soon replaced worldwide other reference temperatures for length measurements that manufacturers of precision equipment had used before, including 0ย ยฐC, 62ย ยฐF, and 25ย ยฐC. Among the reasons for choosing 20ย ยฐC was that this was a comfortable and practical workshop temperature and that it resulted in an integer value on both the Celsius and Fahrenheit scales.
Discussed on
- "ISO 1" | 2013-11-09 | 94 Upvotes 17 Comments
๐ Paradox of tolerance
The paradox of tolerance states that if a society is tolerant without limit, its ability to be tolerant is eventually seized or destroyed by the intolerant. Karl Popper described it as the seemingly paradoxical idea that, "In order to maintain a tolerant society, the society must be intolerant of intolerance." The paradox of tolerance is an important concept for thinking about which boundaries can or should be set.
Discussed on
- "Paradox of Tolerance" | 2020-08-07 | 25 Upvotes 21 Comments
- "Paradox of Tolerance" | 2020-06-04 | 14 Upvotes 5 Comments
- "Paradox of tolerance" | 2019-01-21 | 78 Upvotes 99 Comments
๐ Rabin-Karp Algorithm for finding matching substrings in text
In computer science, the RabinโKarp algorithm or KarpโRabin algorithm is a string-searching algorithm created by Richard M. Karp and Michael O. Rabinย (1987) that uses hashing to find an exact match of a pattern string in a text. It uses a rolling hash to quickly filter out positions of the text that cannot match the pattern, and then checks for a match at the remaining positions. Generalizations of the same idea can be used to find more than one match of a single pattern, or to find matches for more than one pattern.
To find a single match of a single pattern, the expected time of the algorithm is linear in the combined length of the pattern and text, although its worst-case time complexity is the product of the two lengths. To find multiple matches, the expected time is linear in the input lengths, plus the combined length of all the matches, which could be greater than linear. In contrast, the AhoโCorasick algorithm can find all matches of multiple patterns in worst-case time and space linear in the input length and the number of matches (instead of the total length of the matches).
A practical application of the algorithm is detecting plagiarism. Given source material, the algorithm can rapidly search through a paper for instances of sentences from the source material, ignoring details such as case and punctuation. Because of the abundance of the sought strings, single-string searching algorithms are impractical.
Discussed on
- "Rabin-Karp Algorithm for finding matching substrings in text" | 2018-11-20 | 10 Upvotes 1 Comments