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馃敆 Naismith's Rule
Naismith's rule helps with the planning of a walking or hiking expedition by calculating how long it will take to travel the intended route, including any extra time taken when walking uphill. This rule of thumb was devised by William W. Naismith, a Scottish mountaineer, in 1892. A modern version can be formulated as follows:
- Allow one hour for every 3 miles (5聽km) forward, plus an additional hour for every 2,000 feet (600聽m) of ascent.
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- "Naismith's Rule" | 2024-04-11 | 47 Upvotes 14 Comments
馃敆 Mammalian diving reflex
The diving reflex, also known as the diving response and mammalian diving reflex, is a set of physiological responses to immersion that overrides the basic homeostatic reflexes, and is found in all air-breathing vertebrates studied to date. It optimizes respiration by preferentially distributing oxygen stores to the heart and brain, enabling submersion for an extended time.
The diving reflex is exhibited strongly in aquatic mammals, such as seals, otters, dolphins, and muskrats, and exists as a lesser response in other animals, including adult humans, babies up to 6 months old (see infant swimming), and diving birds, such as ducks and penguins.
The diving reflex is triggered specifically by chilling and wetting the nostrils and face while breath-holding, and is sustained via neural processing originating in the carotid chemoreceptors. The most noticeable effects are on the cardiovascular system, which displays peripheral vasoconstriction, slowed heart rate, redirection of blood to the vital organs to conserve oxygen, release of red blood cells stored in the spleen, and, in humans, heart rhythm irregularities. Although aquatic animals have evolved profound physiological adaptations to conserve oxygen during submersion, the apnea and its duration, bradycardia, vasoconstriction, and redistribution of cardiac output occur also in terrestrial animals as a neural response, but the effects are more profound in natural divers.
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- "Mammalian diving reflex" | 2016-03-27 | 73 Upvotes 29 Comments
馃敆 P贸lya Urn Model
In statistics, a P贸lya urn model (also known as a P贸lya urn scheme or simply as P贸lya's urn), named after George P贸lya, is a type of statistical model used as an idealized mental exercise framework, unifying many treatments.
In an urn model, objects of real interest (such as atoms, people, cars, etc.) are represented as colored balls in an urn or other container. In the basic P贸lya urn model, the urn contains x white and y black balls; one ball is drawn randomly from the urn and its color observed; it is then returned in the urn, and an additional ball of the same color is added to the urn, and the selection process is repeated. Questions of interest are the evolution of the urn population and the sequence of colors of the balls drawn out.
This endows the urn with a self-reinforcing property sometimes expressed as the rich get richer.
Note that in some sense, the P贸lya urn model is the "opposite" of the model of sampling without replacement, where every time a particular value is observed, it is less likely to be observed again, whereas in a P贸lya urn model, an observed value is more likely to be observed again. In both of these models, the act of measurement has an effect on the outcome of future measurements. (For comparison, when sampling with replacement, observation of a particular value has no effect on how likely it is to observe that value again.) In a P贸lya urn model, successive acts of measurement over time have less and less effect on future measurements, whereas in sampling without replacement, the opposite is true: After a certain number of measurements of a particular value, that value will never be seen again.
One of the reasons for interest in this particular rather elaborate urn model (i.e. with duplication and then replacement of each ball drawn) is that it provides an example in which the count (initially x black and y white) of balls in the urn is not concealed, which is able to approximate the correct updating of subjective probabilities appropriate to a different case in which the original urn content is concealed while ordinary sampling with replacement is conducted (without the P贸lya ball-duplication). Because of the simple "sampling with replacement" scheme in this second case, the urn content is now static, but this greater simplicity is compensated for by the assumption that the urn content is now unknown to an observer. A Bayesian analysis of the observer's uncertainty about the urn's initial content can be made, using a particular choice of (conjugate) prior distribution. Specifically, suppose that an observer knows that the urn contains only identical balls, each coloured either black or white, but he does not know the absolute number of balls present, nor the proportion that are of each colour. Suppose that he holds prior beliefs about these unknowns: for him the probability distribution of the urn content is well approximated by some prior distribution for the total number of balls in the urn, and a beta prior distribution with parameters (x,y) for the initial proportion of these which are black, this proportion being (for him) considered approximately independent of the total number. Then the process of outcomes of a succession of draws from the urn (with replacement but without the duplication) has approximately the same probability law as does the above P贸lya scheme in which the actual urn content was not hidden from him. The approximation error here relates to the fact that an urn containing a known finite number m of balls of course cannot have an exactly beta-distributed unknown proportion of black balls, since the domain of possible values for that proportion are confined to being multiples of , rather than having the full freedom to assume any value in the continuous unit interval, as would an exactly beta distributed proportion. This slightly informal account is provided for reason of motivation, and can be made more mathematically precise.
This basic P贸lya urn model has been enriched and generalized in many ways.
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- "P贸lya Urn Model" | 2022-03-18 | 59 Upvotes 3 Comments
馃敆 Agloe, New York
Agloe is a fictional hamlet in Colchester, Delaware County, New York, that became an actual landmark after mapmakers made up the community as a phantom settlement, an example of a "copyright trap" and similar to a trap street. Agloe was put onto the map in order to catch plagiarism as it appears only on their map and not on any others. Soon, using fictional "copyright traps" became a typical strategy in mapmaker design to thwart plagiarism. Agloe was known as a "paper town" because of this.
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- "Agloe, New York" | 2015-10-03 | 101 Upvotes 17 Comments
馃敆 Rotterdam harbor storm barrier closes for the first time in its history
The Maeslantkering ("Maeslant barrier" in Dutch) is a storm surge barrier on the Nieuwe Waterweg, in South Holland, Netherlands. It was constructed from 1991 to 1997. As part of the Delta Works the barrier responds to water level predictions calculated by a centralized computer system called BOS. It automatically closes when Rotterdam (especially the Port of Rotterdam) is threatened by floods.
Maeslantkering has two 210-metre long barrier gates, with two 237-metre long steel trusses holding each. When closed, the barrier will protect the entire width (360 metres) of the Nieuwe Waterweg, the main waterway of Port of Rotterdam. It is one of the largest moving structures on Earth, rivalling the Green Bank Telescope in the United States and the Bagger 288 excavator in Germany.
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- "Rotterdam harbor storm barrier closes for the first time in its history" | 2023-12-21 | 38 Upvotes 16 Comments
馃敆 Optacon
The Optacon (OPtical to TActile CONverter) is an electromechanical device that enables blind people to read printed material that has not been transcribed into Braille. The device consists of two parts: a scanner which the user runs over the material to be read, and a finger pad which translates the words into vibrations felt on the finger tips. The Optacon was conceived by John Linvill, a professor of Electrical Engineering at Stanford University, and developed with researchers at Stanford Research Institute (now SRI International). Telesensory Systems manufactured the device from 1971 until it was discontinued in 1996. Although effective once mastered, it was expensive and took many hours of training to reach competency. In 2005, TSI suddenly shut down. Employees were "walked out" of the building and lost accrued vacation time, medical insurance, and all benefits. Customers could not buy new machines or get existing machines fixed. Some work was done by other companies but no device with the versatility of the Optacon had been developed as of 2007. Many blind people continue to use their Optacons to this day. The Optacon offers capabilities that no other device offers including the ability to see a printed page or computer screen as it truly appears including drawings, typefaces, and specialized text layouts.
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- "Optacon" | 2020-01-27 | 92 Upvotes 32 Comments
馃敆 Proxy Firm
A proxy firm (also a proxy advisor, proxy adviser, proxy voting agency, vote service provider or shareholder voting research provider) provides services to shareholders (in most cases an institutional investor of some type) to vote their shares at shareholder meetings of, usually, quoted companies.
The typical services provided include agenda translation, provision of vote management software, voting policy development, company research, and vote administration including vote execution. According to their websites, not all firms provide voting recommendations and those that do may simply execute client voting instructions.
The votes executed are called "Proxy Votes" because the shareholder usually does not attend the meeting and instead sends instructions - a proxy appointment - for a third party, usually the chairman of the meeting to vote shares in accordance with the instructions given on the voting card.
馃敆 rwall Incident (1987)
Jordan K. Hubbard (born April 8, 1963) is an open source software developer, authoring software such as the Ardent Window Manager and various other open source tools and libraries before co-founding the FreeBSD project with Nate Williams and Rodney W. Grimes in 1993, for which he contributed the initial FreeBSD Ports collection, package management system and sysinstall. In July 2001 Hubbard joined Apple Computer in the role of manager of the BSD technology group. In 2005, his title was "Director of UNIX Technology" and in October 2007, Hubbard was promoted to "Director of Engineering of Unix Technologies" at Apple where he remained until June 2013.
On July 15, 2013, he became CTO of iXsystems where he also led the FreeNAS open source project.
On March 24, 2017, he announced his plan to depart from iXsystems and that he would be joining TwoPoreGuys, a Biotechnology company, as VP of Engineering. From January 2019 - April 2020 he was part of the Engineering Leadership team at Uber and, as of April 2020, is currently Sr. Director for GPU Compute SW at NVidia [1].
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- "rwall Incident (1987)" | 2020-11-20 | 21 Upvotes 13 Comments
馃敆 Biophilic Design
Biophilic design is a concept used within the building industry to increase occupant connectivity to the natural environment through the use of direct nature, indirect nature, and space and place conditions. Used at both the building and city-scale, it is argued that this idea has health, environmental, and economic benefits for building occupants and urban environments, with few drawbacks. Although its name was coined in recent history, indicators of biophilic design have been seen in architecture from as far back as the Hanging Gardens of Babylon.
馃敆 Wikipedia's getting a new look
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- "Wikipedia's getting a new look" | 2010-05-11 | 46 Upvotes 27 Comments