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Synopsis: The Coldest Water

A new technique has measured the lowest temperature ever recorded for liquid water. [Physics] Published Tue Jan 02, 2018

Demystifying the Chain Rule in Calculus

Introduction There are a  number of posts on PF involving a general confusion over the multi-vairiable chain rule.  The problem is often caused by a lack of clarity about the roles of functions and variables and what precisely each derivative means.  This insight is an attempt to clarify things. Part A: The Single-Variable Chain Rule […]

A virus-bacteria coevolutionary 'arms race' solves diversity by 'killing the winner'

There is remarkable biodiversity in all but the most extreme ecosystems on Earth. When many species are competing for the same finite resource, a theory called competitive exclusion suggests one species will outperform the others and drive them to extinction, limiting biodiversity. Show More Summary

2nd International Research Conference on Sustainable Energy, Engineering, Materials and Environment

Conference: 25 Jul 2018 - 27 Jul 2018, Mieres, Oviedo, Spain, Spain. Organized by Polytechnic School of Mieres.

Wave attenuation hints at nature of Earth’s asthenosphere

Low viscosity layer enables plate tectonics, but its cause remains unconfirmed

The Schwarzschild Metric: Part 3, A Newtonian Comparison

A Short Proof of Birkoff’s Theorem derived the Schwarzschild metric in units of ##G = c = 1##: \begin{equation} ds^2 = -\left(1 – \frac{2M}{r}\right)dt^2 + \left(1 – \frac{2M}{r}\right)^{-1}dr^2 + r^2d\theta^2 + r^2 \sin^2\theta d\phi^2...Show More Summary

Single metalens focuses all colors of the rainbow in one point; opens new possibilities in virtual, augmented reality

Metalenses—flat surfaces that use nanostructures to focus light—promise to revolutionize optics by replacing the bulky, curved lenses currently used in optical devices with a simple, flat surface. But, these metalenses have remained limited in the spectrum of light they can focus well. Show More Summary

Happy New Year From the Cocktail Party Kitties

There's no physics linkfest this week, if only because so little happens (apart from year-end lists) in science news in the interval between Christmas and New Year's. But we'll be back next week. Meanwhile, here are Caliban (tuxedo) and Ariel...

3 New Years Tips For Cooling Off Debates

Civil discussion and debate is critical to Physics Forums. But it is also important in everyday life. When arguments get overheated, people may avoid engaging with friends and family and the relationships could wither and die.  If the only safe topic you can discuss with your friend is weather, your relationship is in danger. So, […]

How good is your New Year's bubbly? Listen closely

Pop! goes the New Year's corks—and the bubbles that result might point to how high-quality your champagne is, researchers say.

Focus: Detecting Gravitational Waves by Watching Stars

Author(s): Philip Ball A passing gravitational wave produces shifts in the apparent positions of the stars, and these motions should be detectable with the Gaia space telescope. [Physics 10, 138] Published Fri Dec 29, 2017

Viewpoint: 3D Imaging of Hopping Molecules

Author(s): Eli Barkai and Yuval Garini The 3D motion of molecules at a solid-liquid interface is directly imaged for the first time. [Physics 10, 139] Published Fri Dec 29, 2017

The Schwarzschild Metric: Part 2, The Photon Sphere

  A Short Proof of Birkoff’s Theorem derived the Schwarzschild metric in units of ##G = c = 1##: \begin{equation} ds^2 = -\left(1 – \frac{2M}{r}\right)dt^2 + \left(1 – \frac{2M}{r}\right)^{-1}dr^2 + r^2d\theta^2 + r^2 \sin^2\theta d\phi^2...Show More Summary

Christmas Project

Every Christmas I try to do some sort of project. Something new. Sometimes it turns into something real, and last for years. Sometimes it goes no where. Normally, I have an idea of what I’m going to attempt – usually it has been bugging me for months and I can’t wait till break to get […]

Synopsis: Sorting Photons via Their Radial Quantum Number

A new method groups photons based on the radial component of their angular momentum. [Physics] Published Thu Dec 28, 2017

Mathematical Quantum Field Theory – Gauge Fixing

The following is one chapter in a series of Mathematical Quantum Field Theory. The previous chapter is 11. Reduced phase space. The next chapter is 13. Quantization. 12. Gauge fixing While in the previous chapter we had constructed the reduced phase space of a Lagrangian field theory, embodied by the local BV-BRST complex (example 11.21), […]

Highly efficient, high-power short-pulse lasers based on Tm3+ doped materials

Highly efficient high power short pulse lasers at the wavelength range of 2 µm based on Tm3+ doped materials have a variety of applications such as material processing, LiDAR, mid-infrared OPOs for wavelengths up to 12 ?m, or mid-infrared supercontinuum generation. They also would enable direct coherent soft X-ray generation by high order harmonics generation.

The Schwarzschild Metric: Part 1, GPS Satellites

A Global Positioning System (GPS) device gives your precise location by receiving light pulses from satellites with synchronized clocks then triangulating your location based on that information [1]. Since light travels at 300 million meters per second, your location will be off by about 1 meter if the clock times are off by only 3 […]

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