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🔗 Computer science 🔗 Statistics

A Boltzmann machine (also called stochastic Hopfield network with hidden units) is a type of stochastic recurrent neural network. It is a Markov random field. It was translated from statistical physics for use in cognitive science. The Boltzmann machine is based on stochastic spin-glass model with an external field, i.e., a Sherrington–Kirkpatrick model that is a stochastic Ising Model and applied to machine learning.

Boltzmann machines can be seen as the stochastic, generative counterpart of Hopfield networks. They were one of the first neural networks capable of learning internal representations, and are able to represent and (given sufficient time) solve combinatoric problems.

They are theoretically intriguing because of the locality and Hebbian nature of their training algorithm (being trained by Hebb's rule), and because of their parallelism and the resemblance of their dynamics to simple physical processes. Boltzmann machines with unconstrained connectivity have not proven useful for practical problems in machine learning or inference, but if the connectivity is properly constrained, the learning can be made efficient enough to be useful for practical problems.

They are named after the Boltzmann distribution in statistical mechanics, which is used in their sampling function. That's why they are called "energy based models" (EBM). They were invented in 1985 by Geoffrey Hinton, then a Professor at Carnegie Mellon University, and Terry Sejnowski, then a Professor at Johns Hopkins University.

🔗 Time

Solar time is a calculation of the passage of time based on the position of the Sun in the sky. The fundamental unit of solar time is the day. Two types of solar time are apparent solar time (sundial time) and mean solar time (clock time).

🔗 Time

The Doomsday rule is an algorithm of determination of the day of the week for a given date. It provides a perpetual calendar because the Gregorian calendar moves in cycles of 400 years. The algorithm for mental calculation was devised by John Conway in 1973, drawing inspiration from Lewis Carroll's perpetual calendar algorithm. It takes advantage of each year having a certain day of the week, called the doomsday, upon which certain easy-to-remember dates fall; for example, 4/4, 6/6, 8/8, 10/10, 12/12, and the last day of February all occur on the same day of the week in any year. Applying the Doomsday algorithm involves three steps: Determination of the anchor day for the century, calculation of the doomsday for the year from the anchor day, and selection of the closest date out of those that always fall on the doomsday, e.g., 4/4 and 6/6, and count of the number of days (modulo 7) between that date and the date in question to arrive at the day of the week. The technique applies to both the Gregorian calendar and the Julian calendar, although their doomsdays are usually different days of the week.

The algorithm is simple enough that it can be computed mentally. Conway can usually give the correct answer in under two seconds. To improve his speed, he practices his calendrical calculations on his computer, which is programmed to quiz him with random dates every time he logs on.

🔗 Geology 🔗 Rocks and minerals 🔗 Iceland

Iceland spar, formerly called Iceland crystal (Icelandic: silfurberg [ˈsɪlvʏrˌpɛrk], lit. 'silver-rock') and also called optical calcite, is a transparent variety of calcite, or crystallized calcium carbonate, originally brought from Iceland, and used in demonstrating the polarization of light.

🔗 Africa 🔗 Africa/Ghana 🔗 Anthroponymy 🔗 Africa/Togo 🔗 Africa/Benin 🔗 Africa/Ivory Coast

The Akan people of Ghana frequently name their children after the day of the week they were born and the order in which they were born. These "day names" have further meanings concerning the soul and character of the person. Middle names have considerably more variety and can refer to their birth order, twin status, or an ancestor's middle name.

This naming tradition is shared throughout West Africa and the African diaspora. During the 18th–19th centuries, enslaved people in the Caribbean from the region that is modern-day Ghana were referred to as Coromantees. Many of the leaders of enslaved people's rebellions had "day names" including Cuffy, Cuffee or Kofi, Cudjoe or Kojo, Quao or Quaw, and Quamina or Kwame/Kwamina.

Most Ghanaians have at least one name from this system, even if they also have an English or Christian name. Notable figures with day names include Ghana's first president Kwame Nkrumah and former United Nations Secretary-General Kofi Annan.

In the official orthography of the Twi language, the Ashanti versions of these names as spoken in Kumasi are as follows. The diacritics on á a̍ à represent high, mid, and low tone (tone does not need to be marked on every vowel), while the diacritic on a̩ is used for vowel harmony and can be ignored. (Diacritics are frequently dropped in any case.) Variants of the names are used in other languages, or may represent different transliteration schemes. The variants mostly consist of different affixes (in Ashanti, kwa- or ko- for men and a- plus -a or -wa for women). For example, among the Fante, the prefixes are kwe-, kwa or ko for men and e-, arespectively. Akan d̩wo or jo(Fante) is pronounced something like English Joe, but there do appear to be two sets of names for those born on Monday.

🔗 Economics 🔗 Energy 🔗 Globalization

Petrodollar recycling is the international spending or investment of a country's revenues from petroleum exports ("petrodollars"). It generally refers to the phenomenon of major petroleum-exporting nations, mainly the OPEC members plus Russia and Norway, earning more money from the export of crude oil than they could efficiently invest in their own economies. The resulting global interdependencies and financial flows, from oil producers back to oil consumers, can reach a scale of hundreds of billions of US dollars per year – including a wide range of transactions in a variety of currencies, some pegged to the US dollar and some not. These flows are heavily influenced by government-level decisions regarding international investment and aid, with important consequences for both global finance and petroleum politics. The phenomenon is most pronounced during periods when the price of oil is historically high.

The term petrodollar was coined in the early 1970s during the oil crisis, and the first major petrodollar surge (1974–1981) resulted in more financial complications than the second (2005–2014).

In August 2018, Venezuela declared that it would price its oil in Euros, Yuan and other currencies.

🔗 California 🔗 California/San Francisco Bay Area 🔗 Food and drink

Caffè Mediterraneum, often referred to as Caffè Med or simply the Med, was a café located on Telegraph Avenue in Berkeley, California, US, near the University of California, Berkeley. The Med was a landmark of Telegraph Avenue history, "listed for years in European guidebooks as 'the gathering place for 1960s radicals who created People's Park'" and as of 2009 described in Fodor's guidebook as "a relic of 1960s-era café culture". It was located at 2475 Telegraph Avenue, between Dwight Way and Haste Street.

🔗 Professional sound production 🔗 Stagecraft

The Schaffer–Vega diversity system (SVDS) was a wireless guitar system developed in 1975–76, engineered and prototyped by Ken Schaffer in New York City, and manufactured by the Vega Corporation, El Monte, California. A handheld microphone version was introduced in 1977.

The system was the first cordless system to be adopted by major rock acts because it solved technical problems common to earlier wireless systems. The reliable sound and freedom of movement it provided paved the way for bands to tour with large multi-level stages in arenas. Schaffer-Vegas were used in the late 1970s and early 1980s by many rock bands such as Pink Floyd (namely guitarist David Gilmour), the Rolling Stones, AC/DC and Kiss.

🔗 Spaceflight 🔗 Physics 🔗 Physics/relativity

Gravity Probe B (GP-B) was a satellite-based experiment to test two unverified predictions of general relativity: the geodetic effect and frame-dragging. This was to be accomplished by measuring, very precisely, tiny changes in the direction of spin of four gyroscopes contained in an Earth-orbiting satellite at 650 km (400 mi) altitude, crossing directly over the poles.

The satellite was launched on 20 April 2004 on a Delta II rocket. The spaceflight phase lasted until 2005; Its aim was to measure spacetime curvature near Earth, and thereby the stress–energy tensor (which is related to the distribution and the motion of matter in space) in and near Earth. This provided a test of general relativity, gravitomagnetism and related models. The principal investigator was Francis Everitt.

Initial results confirmed the expected geodetic effect to an accuracy of about 1%. The expected frame-dragging effect was similar in magnitude to the current noise level (the noise being dominated by initially unmodeled effects due to nonuniform coatings on the gyroscopes). Work continued to model and account for these sources of error, thus permitting extraction of the frame-dragging signal. By August 2008, the frame-dragging effect had been confirmed to within 15% of the expected result, and the December 2008 NASA report indicated that the geodetic effect was confirmed to be better than 0.5%.

In an article published in the journal Physical Review Letters in 2011, the authors reported analysis of the data from all four gyroscopes results in a geodetic drift rate of −6601.8±18.3 mas/yr and a frame-dragging drift rate of −37.2±7.2 mas/yr, in good agreement with the general relativity predictions of −6606.1±0.28% mas/yr and −39.2±0.19% mas/yr, respectively.

🔗 Scotland 🔗 Theatre 🔗 Shakespeare

The Scottish play and the Bard's play are euphemisms for William Shakespeare's Macbeth. The first is a reference to the play's Scottish setting, the second a reference to Shakespeare’s popular nickname. According to a theatrical superstition, called the Scottish curse, speaking the name Macbeth inside a theatre, other than as called for in the script while rehearsing or performing, will cause disaster. A variation of the superstition also forbids quoting lines from the play within a theatre except as part of an actual rehearsal or performance of the play.

Because of this superstition, the lead character is often referred to as the Scottish King or Scottish Lord. Lady Macbeth is often referred to as the Scottish Lady. Sometimes Mackers or MacB is used to avoid saying the name.