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🔗 Metalworking

Biomachining is the machining process of using lithotropic bacteria to remove material from metal parts, contrasted with chemical machining methods such as chemical milling and physical machining methods such as milling. Certain bacteria, such as Thiobacillus ferrooxidans and Thiobacillus thiooxidans, which are also used in the mineral refinement process of bioleaching, utilize the chemical energy from oxidation of iron or copper to fix carbon dioxide from the air. A metal object, when placed in a culture fluid containing these metal-metabolizing bacteria, will have material removed from its surface over time.

Biomachining is ideal for micromachining due to its very low material removal rate. In addition, biomachining is less likely to leave an undesirable surface finish; neither chemical nor physical energy is concentrated on the cutting area, so the possibility of a damaged or burned surface is slim.

This process has been successfully used to cut both pure iron and pure copper.

🔗 Statistics

In statistics, a Pólya urn model (also known as a Pólya urn scheme or simply as Pólya's urn), named after George Pólya, 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 Pólya 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 Pólya 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 Pólya 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 Pólya 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 Pólya 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 Pólya 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 ${\displaystyle 1/m}$, 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 Pólya urn model has been enriched and generalized in many ways.

🔗 Buses

A bus trap (car trap in the UK) is a metal grate placed over a ditch or pit in the road with tines (sides) spaced far enough apart that small (shorter axle) vehicles fall between the tines but close enough that larger-diameter-wheeled vehicles, such as buses, may pass. Cycles may cross broader sided examples.

Different versions exist for restricting access. The tines cross the path of the road, not parallel with the road direction. Small-wheeled vehicles bottom out in between the tines, preventing the vehicle from continuing over the obstacle.

🔗 Biography 🔗 Poetry 🔗 United Kingdom

The person from Porlock was an unwelcome visitor to Samuel Taylor Coleridge during his composition of the poem Kubla Khan in 1797. Coleridge claimed to have perceived the entire course of the poem in a dream (possibly an opium-induced haze), but was interrupted by this visitor from Porlock while in the process of writing it. Kubla Khan, only 54 lines long, was never completed. Thus "person from Porlock", "man from Porlock", or just "Porlock" are literary allusions to unwanted intruders who disrupt inspired creativity.

🔗 Environment

🔗 Biography

Gregory F. Packer (born December 18, 1963), is a retired American highway maintenance worker from Huntington, New York, best known for frequently being quoted as a "man on the street" in newspapers, magazines and television broadcasts from 1995 to the present. He has been quoted in hundreds of articles and television broadcasts as a member of the public (that is, a "man on the street" rather than a newsmaker or expert). Although he always gives his real name, he has admitted to making things up to get into the paper.

Packer's status as a frequent interviewee is due to a number of factors, including seeking out members of the press and appearing friendly, although mostly it is due to his hobby of attending public appearances of celebrities and other media events and attempting to be first in line on such occasions. This has led to him being dubbed a professional line sitter. It has also led to Packer's other claim to fame: being the first person in the world to buy an iPhone, on June 29, 2007 at Apple Fifth Avenue in New York City, after having camped out for five days in front of the store. (He tried to similarly be the first to buy an iPad in 2010, but was bumped from the first position in line due to not having a reservation.) His efforts to be first in line have also allowed him to meet people including Mariah Carey, Garth Brooks, Dennis Rodman and Ringo Starr, as well as at least four presidents of the United States: Jimmy Carter, Bill Clinton, George W. Bush and (before he became president) Donald Trump.

🔗 Religion 🔗 Christianity 🔗 Israel 🔗 Palestine 🔗 Christianity/Catholicism 🔗 Christianity/Eastern Orthodoxy 🔗 Christianity/Jesus 🔗 Christianity/Oriental Orthodoxy

The Immovable Ladder is a wooden ladder leaning against the right window on the second tier of the facade of the Church of the Holy Sepulchre in the Old City of Jerusalem. The ladder rests on a ledge and is attached to a window owned by the Armenian Apostolic Church. The ladder is a symbol of inter-confessional disputes within Christianity. Its presence in its current location signifies the adherence to an agreement among six Christian denominations, who collectively own the church, not to move, repair, or alter anything in the church without the consent of all six denominations.

🔗 Video games 🔗 Computing

The ZX81 is a home computer that was produced by Sinclair Research and manufactured in Dundee, Scotland, by Timex Corporation. It was launched in the United Kingdom in March 1981 as the successor to Sinclair's ZX80 and designed to be a low-cost introduction to home computing for the general public. It was hugely successful; more than 1.5 million units were sold. In the United States it was initially sold as the ZX-81 under license by Timex. Timex later produced its own versions of the ZX81: the Timex Sinclair 1000 and Timex Sinclair 1500. Unauthorized ZX81 clones were produced in several countries.

The ZX81 was designed to be small, simple, and above all, inexpensive, with as few components as possible. Video output is to a television set rather than a dedicated monitor. Programs and data are loaded and saved onto compact audio cassettes. It uses only four silicon chips and a mere 1 KB of memory. There is no power switch or any moving parts with the exception of a VHF TV channel selector switch present in some models. It has a pressure-sensitive membrane keyboard. The ZX81's limitations prompted a market in third-party peripherals to improve its capabilities. Its distinctive case and keyboard brought designer Rick Dickinson a Design Council award.

The ZX81 could be bought by mail order preassembled or, for a lower price, in kit form. It was the first inexpensive mass-market home computer to be sold by high street stores, led by W. H. Smith and soon many other retailers. The ZX81 marked the point when computing in Britain became an activity for the general public rather than the preserve of businessmen and electronics hobbyists. It produced a huge community of enthusiasts, some of whom founded their own businesses producing software and hardware for the ZX81. Many went on to play major roles in the British computer industry. The ZX81's commercial success made Sinclair Research one of Britain's leading computer manufacturers and earned a fortune and an eventual knighthood for the company's founder Sir Clive Sinclair.

🔗 Cognitive science

Soar is a cognitive architecture, originally created by John Laird, Allen Newell, and Paul Rosenbloom at Carnegie Mellon University. (Rosenbloom continued to serve as co-principal investigator after moving to Stanford University, then to the University of Southern California's Information Sciences Institute.) It is now maintained and developed by John Laird's research group at the University of Michigan.

The goal of the Soar project is to develop the fixed computational building blocks necessary for general intelligent agents – agents that can perform a wide range of tasks and encode, use, and learn all types of knowledge to realize the full range of cognitive capabilities found in humans, such as decision making, problem solving, planning, and natural language understanding. It is both a theory of what cognition is and a computational implementation of that theory. Since its beginnings in 1983 as John Laird’s thesis, it has been widely used by AI researchers to create intelligent agents and cognitive models of different aspects of human behavior. The most current and comprehensive description of Soar is the 2012 book, The Soar Cognitive Architecture.