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🔗 Brands 🔗 Automobiles

The Tweel (a portmanteau of tire and wheel) is an airless tire design developed by the French tire company Michelin. Its significant advantage over pneumatic tires is that the Tweel does not use a bladder full of compressed air, and therefore cannot burst, leak pressure, or become flat. Instead, the Tweel's hub is connected to the rim via flexible polyurethane spokes which fulfil the shock-absorbing role provided by the compressed air in a traditional tire.

🔗 Computer science 🔗 Statistics 🔗 Databases

In data mining and statistics, hierarchical clustering (also called hierarchical cluster analysis or HCA) is a method of cluster analysis that seeks to build a hierarchy of clusters. Strategies for hierarchical clustering generally fall into two categories:

• Agglomerative: This is a "bottom-up" approach: Each observation starts in its own cluster, and pairs of clusters are merged as one moves up the hierarchy.
• Divisive: This is a "top-down" approach: All observations start in one cluster, and splits are performed recursively as one moves down the hierarchy.

In general, the merges and splits are determined in a greedy manner. The results of hierarchical clustering are usually presented in a dendrogram.

Hierarchical clustering has the distinct advantage that any valid measure of distance can be used. In fact, the observations themselves are not required: all that is used is a matrix of distances. On the other hand, except for the special case of single-linkage distance, none of the algorithms (except exhaustive search in ${\displaystyle {\mathcal {O}}(2^{n})}$) can be guaranteed to find the optimum solution.

🔗 Computing 🔗 Computing/Software 🔗 Computing/Free and open-source software

WTFPL is a GPL-compatible permissive license most commonly used as a free software license. As a public domain like license, the WTFPL is essentially the same as dedication to the public domain. It allows redistribution and modification of the work under any terms. The title is an abbreviation of "Do what the fuck you want to Public License".

The first version of the WTFPL, released in March 2000, was written by Banlu Kemiyatorn for his own software project. Sam Hocevar, Debian's former project leader, wrote version 2.

🔗 Biography 🔗 California 🔗 California/San Francisco Bay Area 🔗 Finance & Investment 🔗 Business

Ronald Crawford Conway (born March 9, 1951) is an American angel investor and philanthropist, often described as one of Silicon Valley's "super angels". Conway is recognized as a strong networker.

🔗 Computing 🔗 Computer science

🔗 Computing 🔗 Computing/Networking

In computer networking, IP over Avian Carriers (IPoAC) is a proposal to carry Internet Protocol (IP) traffic by birds such as homing pigeons. IP over Avian Carriers was initially described in RFC 1149, a Request for Comments (RFC) issued by the Internet Engineering Task Force (IETF), written by D. Waitzman, and released on April 1, 1990. It is one of several April Fools' Day Request for Comments.

Waitzman described an improvement of his protocol in RFC 2549, IP over Avian Carriers with Quality of Service (1 April 1999). Later, in RFC 6214—released on 1 April 2011, and 13 years after the introduction of IPv6—Brian Carpenter and Robert Hinden published Adaptation of RFC 1149 for IPv6.

IPoAC has been successfully implemented, but for only nine packets of data, with a packet loss ratio of 55% (due to operator error), and a response time ranging from 3,000 seconds (≈54 minutes) to over 6,000 seconds (≈1.77 hours). Thus, this technology suffers from poor latency. Nevertheless, for large transfers, avian carriers are capable of high average throughput when carrying flash memory devices, effectively implementing a sneakernet. During the last 20 years, the information density of storage media and thus the bandwidth of an avian carrier has increased 3 times as fast as the bandwidth of the Internet. IPoAC may achieve bandwidth peaks of orders of magnitude more than the Internet when used with multiple avian carriers in rural areas. For example: If 16 homing pigeons are given eight 512 GB SD cards each, and take an hour to reach their destination, the throughput of the transfer would be 145.6 Gbit/s, excluding transfer to and from the SD cards.

🔗 Cryptography 🔗 Cryptography/Computer science 🔗 Numismatics 🔗 Numismatics/Cryptocurrency

Hashcash is a proof-of-work system used to limit email spam and denial-of-service attacks, and more recently has become known for its use in bitcoin (and other cryptocurrencies) as part of the mining algorithm. Hashcash was proposed in 1997 by Adam Back and described more formally in Back's 2002 paper "Hashcash - A Denial of Service Counter-Measure".

🔗 Geology 🔗 Geology/Meteorites

Thokcha (Tibetan: ཐོག་ལྕགས, Wylie: thog lcags; also alternatively Tibetan: གནམ་ལྕགས, Wylie: gnam lcags) are tektites and meteorites which serve as amulets. Typically high in iron content, these are traditionally believed to contain a magical, protective power comparable to Tibetan dzi beads. Most thokcha are made of a copper alloy.

The use of meteoric iron has been common throughout the history of ferrous metallurgy. Historically, thokcha were prized for the metallurgical fabrication of weapons, musical instruments, and sacred tools, such as the phurba. Thokcha are an auspicious addition in the metallurgical fabrication of sacred objects cast from panchaloha.

Writer Robert Beer regards meteoric iron as "the supreme substance for forging the physical representation of the vajra or other iron weapons." It was believed that these amulets had been tempered by the celestial gods before falling to Earth. Beer describes the metal falling from space as a metaphor for "the indivisibility of form and emptiness." Many meteorite fragments can be found in Tibet due to its high altitude and open landscape.

🔗 Computing 🔗 Computing/Software

The Zope Object Database (ZODB) is an object-oriented database for transparently and persistently storing Python objects. It is included as part of the Zope web application server, but can also be used independently of Zope.

Features of the ZODB include: transactions, history/undo, transparently pluggable storage, built-in caching, multiversion concurrency control (MVCC), and scalability across a network (using ZEO).