Discussion Forum: August 2016

Monday, August 29, 2016

SI unit 'Ampere' will be replaced by a quantum-based measurement unit

Very soon the ampere -- the SI base unit of electrical current -- will take on an entirely new identity, and NIST scientists are at work on an innovative, quantum-based measurement system that will be consistent with the impending change.

http://www.nist.gov/pml/div684/grp02/counting-down-to-the-new-ampere.cfm

Tuesday, August 23, 2016

Boltzmann: a disordered genius

Born in Vienna on 20 February 1844 during the night between Shrove Tuesday and Ash Wednesday, Boltzmann used to say that this was why his mood could swing so violently from one of great happiness to one of deep depression. It was a tragedy that Boltzmann did not live to experience the glory of his pioneering ideas, for he committed suicide during one such depression in September 1906.

Ludwig Boltzmann: The Man Who Trusted Atoms Carlo Cercignani
1998 Oxford University Press 348pp

Saturday, August 20, 2016

Astronomical Evidence for Dark Matter

Dark matter universe

Most of the mass in the universe is in the form of dark matter—a new type of nonbaryonic particle not yet detected in the laboratory or in other detection experiments. The evidence for the existence of dark matter through its gravitational impact is clear in astronomical observa- tions—from the early observations of the large motions of galaxies in clusters and the motions of stars and gas in galaxies, to observations of the large-scale structure in the universe, gravitational lensing, and the cosmic microwave background.
www.pnas.org/cgi/doi/10.1073/pnas.1516944112

Monday, August 15, 2016

Liquid-filled canyons on Titan

In May 2013 the Cassini RADAR altimeter observed channels in Vid Flumina, a drainage network connected to Titan's second largest hydrocarbon sea, Ligeia Mare. Analysis of these altimeter echoes shows that the channels are located in deep (up to ~570 m), steep-sided, canyons and have strong specular surface reflections that indicate they are currently liquid filled. Elevations of the liquid in these channels are at the same level as Ligeia Mare to within a vertical precision of about 0.7 m, consistent with the interpretation of drowned river valleys. Specular reflections are also observed in lower order tributaries elevated above the level of Ligeia Mare, consistent with drainage feeding into the main channel system.

https://doi.org/10.1002/2016GL069679

Was Venus the First Habitable World of our Solar System?

Present-day Venus is an inhospitable place with surface temperatures approaching 750 K and an atmosphere 90 times as thick as Earth's. Billions of years ago the picture may have been very different. We have created a suite of 3-D climate simulations using topographic data from the Magellan mission, solar spectral irradiance estimates for 2.9 and 0.715 Gya, present-day Venus orbital parameters, an ocean volume consistent with current theory, and an atmospheric composition estimated for early Venus. Using these parameters we find that such a world could have had moderate temperatures if Venus had a rotation period slower than ~16 Earth days, despite an incident solar flux 46 − 70% higher than Earth receives. At its current rotation period, Venus's climate could have remained habitable until at least 715 million years ago. These results demonstrate the role rotation and topography play in understanding the climatic history of Venus-like exoplanets discovered in the present epoch.
https://doi.org/10.1002/2016GL069790

Sunday, August 14, 2016

Science without consensus would be chaos

Scientists and historians who try to estimate what might have happened if, say, Darwin had fallen off the Beagle and drowned, are often accused of playing parlour games.

Revisting the past can help to inform ideas of the present.

http://www.nature.com/news/second-thoughts-1.19934

Glitches in time

Many of today's scientific questions require the reconstruction of accurate histories from data collected with uncertainty in the temporal or spatial measurement process.

A mathematical technique has now been developed that reveals the underlying dynamics of time-dependent data collected with extreme temporal uncertainty, without using additional, costly instrumentation.

https://doi.org/10.1038/532450a

The big question of 'how physics makes us free'

Can it really be that everything you do is determined by facts that were in place long before you were born?

This is the question tackled by Jenann Ismael's book "How Physics Makes Us Free," published recently by Oxford University Press.
http://phys.org/news/2016-04-big-physics-free.html

Peering through Jupiter’s clouds with radio spectral imaging

Radio wavelengths can probe altitudes in Jupiter’s atmosphere below its visible
cloud layers.

http://science.sciencemag.org/content/352/6290/1198

An ice age recorded in the polar deposits of Mars

Layered ice deposits at the poles of Mars record a detailed history of accumulation and erosion related to climate processes. Radar investigations measure these layers and provide evidence for climate changes such as ice advance and retreat.
http://science.sciencemag.org/content/352/6289/1075