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🔗 Electronics

The Williamson amplifier is a four-stage, push-pull, Class A triode-output valve audio power amplifier designed by D. T. N. Williamson during World War II. The original circuit, published in 1947 and addressed to the worldwide do it yourself community, set the standard of high fidelity sound reproduction and served as a benchmark or reference amplifier design throughout the 1950s. The original circuit was copied by hundreds of thousands amateurs worldwide. It was an absolute favourite on the DIY scene of the 1950s, and in the beginning of the decade also dominated British and North American markets for factory-assembled amplifiers.

The Williamson circuit was based on the 1934 Wireless World Quality Amplifier by Walter Cocking, with an additional error amplifier stage and a global negative feedback loop. Deep feedback, triode-connected KT66 power tetrodes, conservative choice of standing currents, and the use of wide-bandwidth output transformer all contributed to the performance of the Williamson. It had a modest output power rating of 15 Watts but surpassed all contemporary designs in having very low harmonic distortion and intermodulation, flat frequency response throughout the audible frequency range, and effective damping of loudspeaker resonances. The 0.1% distortion figure of the Williamson amplifier became the criterion for high fidelity performance that remains valid in the 21st century.

The Williamson amplifier was sensitive to selection and matching of passive components and valves, and prone to unwanted oscillations at infrasonic and ultrasonic frequencies. Enclosing four valve stages and an output transformer in a negative feedback loop was a severe test of design, resulting in a very narrow phase margin or, quite often, no margin at all. Attempts to improve stability of the Williamson could not fix this fundamental flaw. For this reason, and due to high costs of required quality components, manufacturers soon abandoned the Williamson circuit in favour of inherently more stable, cheaper and efficient three-stage, ultralinear or pentode-output designs.

🔗 Visual arts

The Voyage of Life is a series of four paintings created by Thomas Cole in 1842, representing an allegory of the four stages of human life. The paintings, Childhood, Youth, Manhood, and Old Age, depict a voyager who travels in a boat on a river through the mid-19th-century American wilderness. In each painting the voyager rides the boat on the River of Life accompanied by a guardian angel. The landscape, each reflecting one of the four seasons of the year, plays a major role in conveying the story. With each installment the boat's direction of travel is reversed from the previous picture. In childhood, the infant glides from a dark cave into a rich, green landscape. As a youth, the boy takes control of the boat and aims for a shining castle in the sky. In manhood, the adult relies on prayer and religious faith to sustain him through rough waters and a threatening landscape. Finally, the man becomes old and the angel guides him to heaven across the waters of eternity.

🔗 Physics 🔗 Electronics 🔗 Professional sound production

Pink noise or ​¹⁄_f noise is a signal or process with a frequency spectrum such that the power spectral density (energy or power per frequency interval) is inversely proportional to the frequency of the signal. In pink noise, each octave (halving or doubling in frequency) carries an equal amount of noise energy.

Pink noise is one of the most common signals in biological systems.

The name arises from the pink appearance of visible light with this power spectrum. This is in contrast with white noise which has equal intensity per frequency interval.

🔗 Psychology 🔗 Cognitive science

Functional fixedness is a cognitive bias that limits a person to use an object only in the way it is traditionally used. The concept of functional fixedness originated in Gestalt psychology, a movement in psychology that emphasizes holistic processing. Karl Duncker defined functional fixedness as being a "mental block against using an object in a new way that is required to solve a problem". This "block" limits the ability of an individual to use components given to them to complete a task, as they cannot move past the original purpose of those components. For example, if someone needs a paperweight, but they only have a hammer, they may not see how the hammer can be used as a paperweight. Functional fixedness is this inability to see a hammer's use as anything other than for pounding nails; the person couldn't think to use the hammer in a way other than in its conventional function.

When tested, 5-year-old children show no signs of functional fixedness. It has been argued that this is because at age 5, any goal to be achieved with an object is equivalent to any other goal. However, by age 7, children have acquired the tendency to treat the originally intended purpose of an object as special.

🔗 Human rights 🔗 Soviet Union 🔗 History 🔗 Death 🔗 Politics 🔗 Socialism 🔗 Soviet Union/history of Russia 🔗 Soviet Union/Russia

Mass killings under communist regimes occurred throughout the 20th century. Death estimates vary widely, depending on the definitions of the deaths that are included in them. The higher estimates of mass killings account for the crimes that governments committed against civilians, including executions, the destruction of populations through man-made hunger and deaths that occurred during forced deportations and imprisonment, and deaths that resulted from forced labor.

In addition to "mass killings," terms that are used to define such killings include "democide", "politicide", "classicide", and "genocide."

🔗 Apple Inc.

SWEET16 is an interpreted byte-code instruction set invented by Steve Wozniak and implemented as part of the Integer BASIC ROM in the Apple II series of computers. It was created because Wozniak needed to manipulate 16-bit pointer data, and the Apple II was an 8-bit computer.

SWEET16 was not used by the core BASIC code, but was later used to implement several utilities. Notable among these was the line renumbering routine, which was included in the Programmer's Aid #1 ROM, added to later Apple II models and available for user installation on earlier examples.

SWEET16 code is executed as if it were running on a 16-bit processor with sixteen internal 16-bit little-endian registers, named R0 through R15. Some registers have well-defined functions:

• R0 – accumulator
• R12 – subroutine stack pointer
• R13 – stores the result of all comparison operations for branch testing
• R14 – status register
• R15 – program counter

The 16 virtual registers, 32 bytes in total, are located in the zero page of the Apple II's real, physical memory map (at $00–$1F), with values stored as low byte followed by high byte. The SWEET16 interpreter itself is located from $F689 to $F7FC in the Integer BASIC ROM.

According to Wozniak, the SWEET16 implementation is a model of frugal coding, taking up only about 300 bytes in memory. SWEET16 runs at about one-tenth the speed of the equivalent native 6502 code.

🔗 Computing 🔗 Electronics 🔗 Electrical engineering

Charlieplexing (also known as tristate multiplexing, reduced pin-count LED multiplexing, complementary LED drive and crossplexing) is a technique for accessing a large number of LEDs, switches, micro-capacitors or other I/O entities, using very few tri-state logic wires from a microcontroller, these entities being wired as discrete components, x/y arrays, or woven in a diagonally intersecting pattern to form diagonal arrays.

The method uses the tri-state logic capabilities of microcontrollers in order to gain efficiency over traditional multiplexing, each I/O pin being capable, when required, of rapidly changing between the three states, logical 1, logical 0, and high impedance.

This enables these I/O entities (LEDs, switches etc.) to be connected between any two microcontroller I/Os - e.g. with 4 I/Os, each I/O can pair with 3 other I/Os, resulting in 6 unique pairings (1/2, 1/3, 1/4, 2/3, 2/4, 3/4). Only 4 pairings are possible with standard x/y multiplexing (1/3, 1/4, 2/3, 2/4). Also, due to the microcontroller's ability to reverse the polarity of the 6 I/O pairs, the number of LEDS (or diodes) that are uniquely addressable, can be doubled to 12 - adding LEDS 2/1, 3/1, 4/1, 3/2, 4/2 and 4/3.

Although it is more efficient in its use of I/O, a small amount of address manipulation is required when trying to fit Charlieplexing into a standard x/y array.

Other issues that affect standard multiplexing but are exacerbated by Charlieplexing are:

• consideration of current requirements and the forward voltages of the LEDs.
• a requirement to cycle through the in-use LEDs rapidly so that the persistence of the human eye perceives the display to be lit as a whole. Multiplexing can generally be seen by a strobing effect and skewing if the eye's focal point is moved past the display rapidly.

🔗 Film 🔗 Film/Documentary films 🔗 Women scientists

Top Secret Rosies: The Female "Computers" of WWII is a 2010 documentary film directed by LeAnn Erickson. The film is focused on recognizing the contributions of women during WWII, serving as human computers and six of whom went on to program one of the earliest computers, the ENIAC. Their work helped the United States improve the accuracy of weaponry as most conducted ballistics analysis. The film officially premiered on November 1 on PBS.

🔗 Disaster management

The preparedness paradox is the proposition that if a society or individual acts effectively to mitigate a potential disaster such as a pandemic, natural disaster or other catastrophe so that it causes less harm, the avoided danger will be perceived as having been much less serious because of the limited damage actually caused. The paradox is the incorrect perception that there had been no need for careful preparation as there was little harm, although in reality the limitation of the harm was due to preparation. Several cognitive biases can consequently hamper proper preparation for future risks.

🔗 Military history 🔗 Military history/Intelligence 🔗 Military history/World War II

Operation Mincemeat was a successful British deception operation of the Second World War to disguise the 1943 Allied invasion of Sicily. Two members of British intelligence obtained the body of Glyndwr Michael, a tramp who died from eating rat poison, dressed him as an officer of the Royal Marines and placed personal items on him identifying him as the fictitious Captain (Acting Major) William Martin. Correspondence between two British generals that suggested that the Allies planned to invade Greece and Sardinia, with Sicily as merely the target of a feint, was also placed on the body.

Part of the wider Operation Barclay, Mincemeat was based on the 1939 Trout memo, written by Rear Admiral John Godfrey, the director of the Naval Intelligence Division, and his personal assistant, Lieutenant Commander Ian Fleming. With the approval of the British prime minister, Winston Churchill, and the American military commander in the Mediterranean, General Dwight D. Eisenhower, the plan began by transporting the body to the southern coast of Spain by submarine and releasing it close to shore, where it was picked up the following morning by a Spanish fisherman. The nominally neutral Spanish government shared copies of the documents with the Abwehr, the German military intelligence organisation, before returning the originals to the British. Forensic examination showed they had been read and Ultra decrypts of German messages showed that the Germans fell for the ruse. German reinforcements were shifted to Greece and Sardinia before and during the invasion of Sicily; Sicily received none.

The full effect of Operation Mincemeat is not known, but Sicily was liberated more quickly than anticipated and losses were lower than predicted. The events were depicted in Operation Heartbreak, a 1950 novel by the former cabinet minister Duff Cooper, before one of the intelligence officers who planned and carried out Mincemeat, Ewen Montagu, wrote a history in 1953. Montagu's book formed the basis for the 1956 British film The Man Who Never Was. A second British film was released in 2021, titled Operation Mincemeat. It also has been adapted into a musical.