diffraction imaging


February 28th 1953: Watson and Crick discover DNA structure

On this day in 1953, scientists James D. Watson and Francis Crick discovered the chemical structure of DNA. They made the discovery of the double helix structure while building a cardboard model of the molecule in their laboratory at Cambridge University. Their model of DNA was based on an X-ray diffraction image taken by Rosalind Franklin and the fact that DNA bases are paired; due to her gender, Franklin is often forgotten in narratives of scientific history. Watson and Crick first announced their discovery to friends and it was not formally announced to the wider scientific community until April 25th. Watson, Crick and Maurice Wilkins were jointly awarded the 1962 Nobel Prize for Physiology or Medicine for their discoveries. The discovery was a groundbreaking moment for science, and lay the foundations for the research into DNA and the investigation of human genetics.

“We have found the secret of life.”
- Francis Crick

anonymous asked:

Can we talk about the double slit experiment?


Essentially, the double slit experiment shows that light exhibits dual wave/particle behaviour. It was first offered up by Thomas Young in the late nineteenth century, which is why it’s called the Young’s Double Slit Experiment.

Here’s how it goes down: A monochromatic (single colour/wavelength) light is shone towards a blank screen, and placed between them is a screen with two parallel slits cut into it. If light is just a particle, then it would simply shine through the slits and hit the blank screen in two lines, kind of how spray paint can follows the shape of a stencil. But it doesn’t. It shines on the screen as parallel bands, or fringes.

(Image Credit)

This is because in this instance, light is acting like a wave, so when it passes through the slits, it diffracts—i.e., it spreads out after passing through a narrow opening. This happens from both openings, so  instead of two straight beams of particles, the light becomes two diffracting waves, like this:

(Image Credit)

As they both hit the screen, at some points the waves will meet crest-to-crest, which increases the intensity of the wave (constructive interference), and at other points they’ll meet crest-to-trough, which decreases the intensity of the wave because they cancel each other out (destructive interference). On the screen, the bright lines correspond to the maximum intensities, and the dark lines correspond to the minimum intensities. The combination of these is called an interference pattern.

This experiment is important because it shows that photons can also act as waves, since particles don’t diffract, thus demonstrating the principle of wave-particle duality!

Rosalind Franklin (25 July 1920 - 16 April 1958)

Rosalind Franklin is considered a pioneer molecular biologist who greatly contributed to the understanding of the fine molecular structure of DNA, RNA, viruses, coal, and graphite. Specifically, she is best know for her work on the X-ray diffraction images of DNA which led to the discovery of the DNA double helix. Crick and Watson’s 1953 model regarding the structure of DNA would not have been possible without her data. Franklin’s images of X-ray diffraction (shown above), which confirmed the helical structure of DNA, were shown to Watson without her approval or knowledge. For this reason, there is possibly no other female scientist with as much controversy surrounding her work. 

Franklin knew she wanted to be a scientist from an early age (15) and studied at Cambridge and graduated in 1941. After Cambridge, she spent three years in Paris where she learned X-ray diffraction techniques. She then returned to London in 1951 to work in John Randall’s laboratory at King’s College. It was there that Randall gave Franklin responsibility for her DNA project and where she met Wilkins. Wilkins was away when she was first hired on, and apparently when he returned he misunderstood her role and assumed she was a technical assistant, when she was in fact his peer. During her work on the DNA project (1951-1953) she came very close to solving the DNA structure. She was beaten to publication by Crick and Watson, which some believe could be attributed to the friction between Wilkins and herself. Wilkins showed Watson one of Franklin’s photographs of DNA, and apparently when Watson saw the photo the solution came to him. 

James Watson, Francis Crick, and Maurice Wilkins received a Nobel prize in Physiology or Medicine for the double-helix model of DNA in 1962. This was four years following Franklin’s death at age 37 from ovarian cancer. Debate on the amount of credit due to Franklin for the DNA model continues to this day. 

“Science and everyday life cannot and should not be separated." 


The James Webb Space Telescope just got a super cool upgrade:

A starshade.

The JWST is the heir to the Hubble Space Telescope. It launches in a few years and it’s going to be much more powerful than it’s predecessor. The addition of a starshade will give the telescope the ability to directly photograph exoplanets in other solar systems. It really doesn’t get much more badass than that.

How it works is, when the JWST is in space, the starshade floats in front of it, strategically blocking out the light from alien stars, allowing us to look at planets without their host star’s light diffracting into the image.

By 2018, we’ll likely start receiving actually *good* photographs of planets outside our solar system.

a double helix never tasted so good;


This waiting room’s, like, super muggy and hot and Cosima’s wondering if the owner of this place should be trusted with her baby if they can’t buy a working air conditioner, but. That’s besides the point. The point is, she’s sweating, droplets sliding between her breasts and honestly, if she’s being legit, she’s not opposed to stripping off her thousand-degree sweater down to her tank. (Summer sucks.)

Except, summer totally rocks. Especially when it’s catering long-legged blondes, hair tied up hastily, shorts barely long enough, and, holy hell, breezy white tank top and underneath, God help her, a black, complicatedly-strapped bra. Cosima’s opinions on summer are definitely changing.

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