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🔗 Technology 🔗 Military history 🔗 Military history/Military aviation 🔗 Military history/North American military history 🔗 Military history/Military science, technology, and theory 🔗 Military history/Weaponry 🔗 Canada 🔗 Architecture 🔗 United Kingdom 🔗 Military history/Maritime warfare 🔗 Military history/World War II 🔗 Engineering 🔗 Ships 🔗 Military history/Canadian military history 🔗 Military history/European military history 🔗 Military history/British military history

Project Habakkuk or Habbakuk (spelling varies) was a plan by the British during the Second World War to construct an aircraft carrier out of pykrete (a mixture of wood pulp and ice) for use against German U-boats in the mid-Atlantic, which were beyond the flight range of land-based planes at that time. The idea came from Geoffrey Pyke, who worked for Combined Operations Headquarters. After promising scale tests and the creation of a prototype on a lake (Patricia Lake, Jasper National Park) in Alberta, Canada, the project was shelved due to rising costs, added requirements, and the availability of longer-range aircraft and escort carriers which closed the Mid-Atlantic gap the project was intended to address.

🔗 Computing 🔗 Computing/Computer hardware

The Dadda multiplier is a hardware binary multiplier design invented by computer scientist Luigi Dadda in 1965. It uses a selection of full and half adders to sum the partial products in stages (the Dadda tree or Dadda reduction) until two numbers are left. The design is similar to the Wallace multiplier, but the different reduction tree reduces the required number of gates (for all but the smallest operand sizes) and makes it slightly faster (for all operand sizes).

Dadda and Wallace multipliers have the same three steps for two bit strings ${\displaystyle w_{1}}$ and ${\displaystyle w_{2}}$ of lengths ${\displaystyle \ell _{1}}$ and ${\displaystyle \ell _{2}}$ respectively:

1. Multiply (logical AND) each bit of ${\displaystyle w_{1}}$, by each bit of ${\displaystyle w_{2}}$, yielding ${\displaystyle \ell _{1}\cdot \ell _{2}}$ results, grouped by weight in columns
2. Reduce the number of partial products by stages of full and half adders until we are left with at most two bits of each weight.
3. Add the final result with a conventional adder.

As with the Wallace multiplier, the multiplication products of the first step carry different weights reflecting the magnitude of the original bit values in the multiplication. For example, the product of bits ${\displaystyle a_{n}b_{m}}$ has weight ${\displaystyle n+m}$.

Unlike Wallace multipliers that reduce as much as possible on each layer, Dadda multipliers attempt to minimize the number of gates used, as well as input/output delay. Because of this, Dadda multipliers have a less expensive reduction phase, but the final numbers may be a few bits longer, thus requiring slightly bigger adders.

🔗 Lists 🔗 Statistics

Many probability distributions that are important in theory or applications have been given specific names.

🔗 Geography 🔗 Antarctica 🔗 Glaciers

A blue iceberg is visible after the ice from above the water melts, causing the smooth portion of ice from below the water to overturn. The rare blue ice is formed from the compression of pure snow, which then develops into glacial ice.

Icebergs may also appear blue due to light refraction and age. Older icebergs reveal vivid hues of green and blue, resulting from a high concentration of color, microorganisms, and compacted ice. One of the better known blue icebergs rests in the waters off Sermilik fjord near Greenland. It is described as an electric blue iceberg and is known to locals as "blue diamond".

🔗 Astronomy

In astronomy, the lithium problem or lithium discrepancy refers to the discrepancy between the primordial abundance of lithium as inferred from observations of metal-poor (Population II) halo stars in our galaxy and the amount that should theoretically exist due to Big Bang nucleosynthesis+WMAP cosmic baryon density predictions of the CMB. Namely, the most widely accepted models of the Big Bang suggest that three times as much primordial lithium, in particular lithium-7, should exist. This contrasts with the observed abundance of isotopes of hydrogen (¹H and ²H) and helium (³He and ⁴He) that are consistent with predictions. The discrepancy is highlighted in a so-called "Schramm plot", named in honor of astrophysicist David Schramm, which depicts these primordial abundances as a function of cosmic baryon content from standard BBN predictions.

🔗 Computing 🔗 Computing/Software 🔗 Computing/Amiga 🔗 Project-independent assessment

Amiga Unix (informally known as Amix) is a discontinued full port of AT&T Unix System V Release 4 operating system developed by Commodore-Amiga, Inc. in 1990 for the Amiga computer family as an alternative to AmigaOS, which shipped by default. Bundled with the Amiga 3000UX, Commodore's Unix was one of the first ports of SVR4 to the 68k architecture. The Amiga A3000UX model even got the attention of Sun Microsystems, though ultimately nothing came of it.

Unlike Apple's A/UX, Amiga Unix contained no compatibility layer to allow AmigaOS applications to run under Unix. With few native applications available to take advantage of the Amiga's significant multimedia capabilities, it failed to find a niche in the quite-competitive Unix workstation market of the early 1990s. The A3000UX's price tag of $4,998 (equivalent to $9,382 in 2019) was also not very attractive compared to other Unix workstations at the time, such as the NeXTstation ($5,000 for a base system, with a full API and many times the number of applications available), the SGI Indigo (starting at $8,000), or the Personal DECstation 5000 Model 25 (starting at $5,000). Sun, HP, and IBM had similarly priced systems. The A3000UX's 68030 was noticeably underpowered compared to most of its RISC-based competitors.

Unlike typical commercial Unix distributions of the time, Amiga Unix included the source code to the vendor-specific enhancements and platform-dependent device drivers (essentially any part that wasn't owned by AT&T), allowing interested users to study or enhance those parts of the system. However this source code was subject to the same license terms as the binary part of the system – it was not free software. Amiga Unix also incorporated and depended upon many open source components, such as the GNU C Compiler and X Window System, and included their source code.

Like many other proprietary Unix variants with small market shares, Amiga Unix vanished into the mists of computer history when its vendor, Commodore, went out of business. Today, Unix-like operating systems such as Minix, NetBSD, and Linux are available for the Amiga platform.

🔗 Computing 🔗 Computing/Early computers

The TX-0, for Transistorized Experimental computer zero, but affectionately referred to as tixo (pronounced "tix oh"), was an early fully transistorized computer and contained a then-huge 64K of 18-bit words of magnetic core memory. Construction of the TX-0 began in 1955 and ended in 1956. It was used continually through the 1960s at MIT. The TX-0 incorporated around 3600 Philco high-frequency surface-barrier transistors, the first transistor suitable for high-speed computers. The TX-0 and its direct descendant, the original PDP-1, were platforms for pioneering computer research and the development of what would later be called computer "hacker" culture.

🔗 Linguistics

Ghoti is a creative respelling of the word fish, used to illustrate irregularities in English spelling and pronunciation.

🔗 Biology 🔗 Insects 🔗 Ecology

A hyperparasite, also known as a metaparasite is a parasite whose host, often an insect, is also a parasite, often specifically a parasitoid. Hyperparasites are found mainly among the wasp-waisted Apocrita within the Hymenoptera, and in two other insect orders, the Diptera (true flies) and Coleoptera (beetles). Seventeen families in Hymenoptera and a few species of Diptera and Coleoptera are hyperparasitic. Hyperparasitism developed from primary parasitism, which evolved in the Jurassic period in the Hymenoptera. Hyperparasitism intrigues entomologists because of its multidisciplinary relationship to evolution, ecology, behavior, biological control, taxonomy, and mathematical models.

🔗 Islands 🔗 Lakes

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