Lifeboat Foundation

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Across many scientific domains, there is a common need to automatically extract a simplified view or coarse-graining of how a complex system’s components interact. This general task is called community detection in networks and is analogous to searching for clusters in independent vector data. It is common to evaluate the performance of community detection algorithms by their ability to find so-called ground truth communities. This works well in synthetic networks with planted communities because these networks’ links are formed explicitly based on those known communities. However, there are no planted communities in real-world networks. Instead, it is standard practice to treat some observed discrete-valued node attributes, or metadata, as ground truth. We show that metadata are not the same as ground truth and that treating them as such induces severe theoretical and practical problems. We prove that no algorithm can uniquely solve community detection, and we prove a general No Free Lunch theorem for community detection, which implies that there can be no algorithm that is optimal for all possible community detection tasks. However, community detection remains a powerful tool and node metadata still have value, so a careful exploration of their relationship with network structure can yield insights of genuine worth. We illustrate this point by introducing two statistical techniques that can quantify the relationship between metadata and community structure for a broad class of models. We demonstrate these techniques using both synthetic and real-world networks, and for multiple types of metadata and community structures.

A previously-used Falcon 9 booster soared to life at California’s Vandenberg Air Force Base on Sunday for its Static Fire test ahead of lifting the fifth set of Iridium-NEXT communications satellites on Thursday, marking the start of a string of Falcon 9 missions lined up for March and April. Liftoff is targeting 14:19 UTC on March 29 to boost the number of Iridium-NEXT satellites in orbit to 50 as the Virginia-based communications company continues pushing toward having the full Iridium-NEXT constellation in operation by the end of summer.

Sunday’s Static Fire test occurred near the opening of the day’s test window at 7 a.m. and was expected to run for seven seconds to exercise the nine previously-flown Merlin 1D engines of Booster 1041, gearing up for its second Low Earth Orbit mission. The booster was first in action for the third Iridium-NEXT mission in October 2017 and successfully returned via a Drone Ship landing in the Pacific Ocean as SpaceX has yet to conduct its first return-to-launch-site recovery from Vandenberg.

Investigators will study video, design plans and the “accelerated bridge construction” method for clues.

• By Martin Gordon, The Conversation US on March 25, 2018

New article in Republican Herald out with #transhumanism for Palm Sunday:

Today is Palm Sunday, the first day of Holy Week. It is a week of great drama, but not of tragedy. A few days after his triumphal entry into Jerusalem, Christ will be crucified. On Easter, the first day of a new week, he will rise from the dead to live eternally.

Belief in this resurrection is the core of Christian faith, and on Easter Christians proclaim, “Oh death, where is thy sting? O grave, where is thy victory?”

Continue reading “Life, death, immortality, the 21st century way” »

The ULTRACAM has been a staple in ESO for almost 16 years. This high-speed camera is able to do 500 photographs per second in three different wavelengths and, since 2002 has been operating at the William Herschel Telescope at La Palma (Canary Islands, Spain), the New Technology Telescope at La Silla (Chile) (where this picture was taken) and, most recently, at the Very Large Telescope at Paranal (Chile) and the Thai National Telescope at Chiang Mai (Thailand).

Some of its past targets have included: the study of black holes, “hot-Jupiters” or variable stars.

In a first, amateur aurora chasers brought Steve, a new type of aurora, to the notice of scientists, who discovered that a distinct phenomenon drives its formation.

An interactive site shows Earth 600 million years ago, and lots and lots about dinosaurs.

By pitting AIs against one another, tech companies are creating realistic computer-generated images