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🔗 Mathematics 🔗 Statistics

The secretary problem is a problem that demonstrates a scenario involving optimal stopping theory. The problem has been studied extensively in the fields of applied probability, statistics, and decision theory. It is also known as the marriage problem, the sultan's dowry problem, the fussy suitor problem, the googol game, and the best choice problem.

The basic form of the problem is the following: imagine an administrator who wants to hire the best secretary out of ${\displaystyle n}$ rankable applicants for a position. The applicants are interviewed one by one in random order. A decision about each particular applicant is to be made immediately after the interview. Once rejected, an applicant cannot be recalled. During the interview, the administrator gains information sufficient to rank the applicant among all applicants interviewed so far, but is unaware of the quality of yet unseen applicants. The question is about the optimal strategy (stopping rule) to maximize the probability of selecting the best applicant. If the decision can be deferred to the end, this can be solved by the simple maximum selection algorithm of tracking the running maximum (and who achieved it), and selecting the overall maximum at the end. The difficulty is that the decision must be made immediately.

The shortest rigorous proof known so far is provided by the odds algorithm (Bruss 2000). It implies that the optimal win probability is always at least ${\displaystyle 1/e}$ (where e is the base of the natural logarithm), and that the latter holds even in a much greater generality (2003). The optimal stopping rule prescribes always rejecting the first ${\displaystyle \sim n/e}$ applicants that are interviewed and then stopping at the first applicant who is better than every applicant interviewed so far (or continuing to the last applicant if this never occurs). Sometimes this strategy is called the ${\displaystyle 1/e}$ stopping rule, because the probability of stopping at the best applicant with this strategy is about ${\displaystyle 1/e}$ already for moderate values of ${\displaystyle n}$. One reason why the secretary problem has received so much attention is that the optimal policy for the problem (the stopping rule) is simple and selects the single best candidate about 37% of the time, irrespective of whether there are 100 or 100 million applicants.

🔗 Spaceflight

A porkchop plot (also pork-chop plot) is a chart that shows contours of equal characteristic energy (C₃) against combinations of launch date and arrival date for a particular interplanetary flight.

By examining the results of the porkchop plot, engineers can determine when launch opportunities exist (a launch window) that is compatible with the capabilities of a particular spacecraft. A given contour, called a porkchop curve, represents constant C₃, and the center of the porkchop the optimal minimum C₃. The orbital elements of the solution, where the fixed values are the departure date, the arrival date, and the length of the flight, were first solved mathematically in 1761 by Johann Heinrich Lambert, and the equation is generally known as Lambert's problem (or theorem).

🔗 Medicine 🔗 Science

The aesthetic–usability effect describes a paradox that people perceive more aesthetic designs as much more intuitive than those considered to be less aesthetically pleasing. The effect has been observed in several experiments and has significant implications regarding the acceptance, use, and performance of a design. Usability and aesthetics are the two most important factors in assessing the overall user experience for an application. Usability and aesthetics are judged by a user's reuse expectations, and then their post-use, or experienced, final judgement. A user's cognitive style can influence how they interact with and perceive an application, which in turn can influence their judgement of the application.

🔗 Mathematics

Wang tiles (or Wang dominoes), first proposed by mathematician, logician, and philosopher Hao Wang in 1961, are a class of formal systems. They are modelled visually by square tiles with a color on each side. A set of such tiles is selected, and copies of the tiles are arranged side by side with matching colors, without rotating or reflecting them.

The basic question about a set of Wang tiles is whether it can tile the plane or not, i.e., whether an entire infinite plane can be filled this way. The next question is whether this can be done in a periodic pattern.

🔗 Computing 🔗 Computer Security 🔗 Computer Security/Computing 🔗 Computing/Computer Security 🔗 Computing/Networking

Warchalking is the drawing of symbols in public places to advertise an open Wi-Fi network. Inspired by hobo symbols, the warchalking marks were conceived by a group of friends in June 2002 and publicised by Matt Jones who designed the set of icons and produced a downloadable document containing them. Within days of Jones publishing a blog entry about warchalking, articles appeared in dozens of publications and stories appeared on several major television news programs around the world.

The word is formed by analogy to wardriving, the practice of driving around an area in a car to detect open Wi-Fi nodes. That term in turn is based on wardialing, the practice of dialing many phone numbers hoping to find a modem.

Having found a Wi-Fi node, the warchalker draws a special symbol on a nearby object, such as a wall, the pavement, or a lamp post. Those offering Wi-Fi service might also draw such a symbol to advertise the availability of their Wi-Fi location, whether commercial or personal.

🔗 Environment 🔗 Energy

Pumped-storage hydroelectricity (PSH), or pumped hydroelectric energy storage (PHES), is a type of hydroelectric energy storage used by electric power systems for load balancing. The method stores energy in the form of gravitational potential energy of water, pumped from a lower elevation reservoir to a higher elevation. Low-cost surplus off-peak electric power is typically used to run the pumps. During periods of high electrical demand, the stored water is released through turbines to produce electric power.

Pumped-storage hydroelectricity allows energy from intermittent sources (such as solar, wind) and other renewables, or excess electricity from continuous base-load sources (such as coal or nuclear) to be saved for periods of higher demand. The reservoirs used with pumped storage can be quite small when contrasted with the lakes of conventional hydroelectric plants of similar power capacity, and generating periods are often less than half a day.

The round-trip efficiency of PSH generally varies between 70%–80%. Although the losses of the pumping process make the plant a net consumer of energy overall, the system increases revenue by selling more electricity during periods of peak demand, when electricity prices are highest. If the upper lake collects significant rainfall or is fed by a river then the plant may be a net energy producer in the manner of a traditional hydroelectric plant.

Pumped storage is by far the largest-capacity form of grid energy storage available, and, as of 2020, PSH accounts for around 95% of all active storage installations worldwide, with a total installed throughput capacity of over 181 GW and a total installed storage capacity of over 1.6 TWh.

The main requirement for PSH is hilly country. The global greenfield pumped hydro atlas lists more than 600,000 potential sites around the world, which is about 100 times more than needed to support 100% renewable electricity. Most are closed-loop systems away from rivers. Areas of natural beauty and new dams on rivers can be avoided because of the very large number of potential sites. Some projects utilise existing reservoirs (dubbed "bluefield") such as the 350 Gigawatt-hour Snowy 2.0 scheme under construction in Australia. Some recently proposed projects propose to take advantage of "brownfield" locations such as disused mines such as the Kidston project under construction in Australia.

Water requirements for PSH are small: about 1 gigalitre of initial fill water per gigawatt-hour of storage. This water is recycled uphill and back downhill between the two reservoirs for many decades, but evaporation losses (beyond what rainfall and any inflow from local waterways provide) must be replaced. Land requirements are also small: about 10 hectares per gigawatt-hour of storage, which is much smaller than the land occupied by the solar and windfarms that the storage might support. Closed loop (off-river) pumped hydro storage has the smallest carbon emissions per unit of storage of all candidates for large-scale energy storage.

🔗 History 🔗 Lists 🔗 Geography 🔗 Israel 🔗 Palestine

The population of the region of Palestine, which approximately corresponds to modern Israel, the Palestinian territories and Jordan, has varied in both size and ethnic composition throughout its history.

The following table shows the total population and that of the main ethno-religious groups living in the area from the First Century CE up until the last full calendar year of the British Mandate, 1947.

Note: Figures prior to the 1500s are all only estimates by researchers. For some periods, there are multiple researchers who have made differing estimates. None should be taken as exact numbers, and further context and detail is available by following links to the full description on Wikipedia as well as links to the original information sources.

^†including what is today the Kingdom of Jordan

🔗 Islands 🔗 Lakes

A recursive island or lake is an island or lake that is itself within an island or lake.

🔗 Cetaceans

The 52-hertz whale is an individual whale of unidentified species which calls at the very unusual frequency of 52 Hz. This pitch is a much higher frequency than that of the other whale species with migration patterns most closely resembling this whale's – the blue whale (10–39 Hz) or fin whale (20 Hz). It has been detected regularly in many locations since the late 1980s and appears to be the only individual emitting a whale call at this frequency. It has been described as the "world's loneliest whale".

🔗 Psychology 🔗 Indonesia 🔗 Southeast Asia 🔗 Malaysia 🔗 Southeast Asia/Brunei

Running amok, sometimes referred to as simply amok or having gone amok, also spelled amuck or amuk, from the Southeast Asian Austronesian languages (especially Malaysian and Indonesian), is "an episode of sudden mass assault against people or objects usually by a single individual following a period of brooding that has traditionally been regarded as occurring especially in Malay culture but is now increasingly viewed as psychopathological behavior". The syndrome of "Amok" is found in the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV TR). The phrase is often used in a less serious manner when describing something that is wildly out of control or causing a frenzy (e.g., a dog tearing up the living room furniture might be termed as "running amok").