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OpenLearn Live: 1st December 2016

Updated Thursday 1st December 2016

Pressure ridges in ice - and the danger they present; an Aids vaccine undergoes trial and a range of advent calendars. Learning and research across the day.

OpenLearn Live plucks the green triangles from the big tin of online learning and research. (Feel free to substitute your own favourite Quality Street to repair the metaphor). This page will be updated across the day.

Yesterday we celebrated St Andrew and explored the lottery hack

On this day last year: Christmas lights and your wifi, pauper's graves and the only South Korean in space

See the complete collection of OpenLearn live

Today's posts

World Aids Day

December 1st is also World Aids Day.

In South Africa, trials are taking place of a vaccine which might change the future shape of the disease:

See our World Aids Day collection


It's the first day of December, the double issue of Radio Times is in the shops in just two days, and the catering staff are all weaing santa hats with flashing red lights.

It's advent, in other words.

And there's any number of online advent calendars to choose from. Amongst those that have caught out eyes:

The Ashmolean Museum:

The Postcard Project:

The Sharquairium's eco-ocean calendar:

And, of course, we've cranked up the traditional OpenLearn advent calendar.

Why is a £5 note like the Mary Rose?

You might have guessed this one - they both have a small amount of tallow in them.

Here's the BBC on how beef by-product turned up in your wallet:

Because it turns out the plastic polymer it's made from also contains small amounts of tallow, derived from animal waste products - and some vegetarians are not happy.

Familiar to previous generations as the base for every day staples such as soap and candles, tallow is traditionally derived from beef or mutton (but sometimes pork) at the slaughterhouse or later in the food production process.

And here's the Mary Rose museum on where they found tallow on Henry VIII's ill-fated flagship:

72 candle fragments were found in a cask in the orlop deck of the Mary Rose, many of which were made of beef fat, or tallow.

If you're really interested in the history of tallow, the rules of Leicester Guild of Tallow Chandlers are unique in that they are the medieval documents of their type to have been preserved. You can read them at the University of Leicester website

Ice pack: Pressure ice ridges

Every day this week we're starting with a look at the wonderful world of ice. Yesterday, we were in your fridge looking at ice spikes. Today, we're looking at ice ridges, which are furthermore known as pressure ridges.

An ice pressure ridge near Scott Base, Antarctica Copyrighted image Icon Copyright: NASA A pressure ridge near Scott Base, Antarcticia

The ice that covers the frozen seas keeps moving. And sometimes these can be giant sheets of ice just floating about on the surface. As you might expect, when two floating pieces of ice collide, the ice has to go somewhere - and if the sheet can't continue sideways, it has to go up or down. Or - more often - in both directions. The bit above the base level of the ice is called a ridge; the part underneath, an ice keel.

You'll know that an iceberg is more about what's underneath the water than what stands proud; the same is usually true of a pressure ridge - a keel may reach down nine times as deep as far as a ridge towers above the surface. This makes people charged with captaining icebreakers cautious. A small hump on the surface may indicate a deep keel; and that could lead to ice breaking icebreaker rather than the other way round.

It's ridges and keels which makes the Northwest Passage unusable as a shipping route.

Away from the sea, though, pressure ridges are dangerous not because of their depth, but because they hide thin ice. This news report explains more:

On lakes, pressure ridges are a sign of weakness. Lake Ice describes how they form:

Ridges typically form after a cold spell comes to an end.  As the ice warms thermal expansion puts compression stress in the ice as it pushes into the shoreline around the lake.  When the stress exceeds the compressive strength of the ice it ruptures.  Points of land create stress risers that make it more likely that the rupture will occur there. 

It's that combination of closeness to shore and weakness of ice that leads to accidents like the one in our video.

Explore the Frozen Planet in more depth





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