"We have purposely avoided directly confronting the issue of masks because it is such an emotional and political issue. Like waving a red flag in front of a bull, the topic elicits strong emotions which overwhelms

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Get a cup of coffee.

In this thread, we'll cover *State Quantities* and *Flow Quantities*.

This mental model can help us analyze many different entities -- from complex engineering systems to publicly traded companies.

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A "State Quantity" is something that's associated with a *specific point in time*.

For example, the number of followers a Twitter account has is a state quantity. This number can go up and down over time. But at any one *specific* time point, it's fixed.

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Similarly, the amount of cash a company has is a state quantity.

This cash balance can also rise and fall over time.

But pick any one *specific* time point -- and the company can only have one *specific* cash balance at that time point.

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By contrast, a "Flow Quantity" is something that's associated with a time *interval* rather than a time *point*.

For example, the number of followers gained by a Twitter account is a flow quantity. It's meaningful only when we specify a time interval (eg, the last 30 days).

5/

A simple analogy is that a State Quantity is like a photo -- a snapshot at a particular *point* in time.

But a Flow Quantity is like a video -- a record of events that take place during a particular time *interval*.

And since today is International Day of Women and Girls in Science, let's highlight a few of them - just a few women among thousands of others who helped shape the world we live in today.

Thread.

Dorothy Hodgkin discovered the structure of insulin after 36 years of work.

"I was captured for life by chemistry and by crystals."

Sophia Jex-Blake fought for women's rights to study medicine. She was involved in founding two medical schools for women.

"It seemed discreditable to Great Britain that all her daughters who desired a University education should be driven abroad to seek it."

Alice Augusta Ball developed the "Ball Method", the most effective treatment for leprosy during the early 20th century. She was 23.

Ada Lovelace is regarded as the first to recognize the full potential of computers and as one of the first computer programmers.

“That brain of mine is something more than merely mortal; as time will show.”

In a number of Sunday papers:
Scientific advisers said it was “hard to see” when the restrictions would end as new variants continued to emerge, delivering a potentially devastating blow to the travel industry. The prime minister said that after progress with vaccinations...

...”what we don’t want to see is all that work undone by the arrival of a new variant that is vaccine-busting”.
The idea is planted in people’s mind that this virus is mutating in such a way as to evade prior immunity. This is completely unfounded, certainly as regards immunity..

...gained naturally, after repelling the virus (which well around 99.9% of the population do, fewer, obviously in the very elderly & already ill, more in those younger & well). It’s important to appreciate that upon infection, the human immune system cuts up an infectious...

...agent into short pieces. Each of these short pieces of protein are presented to other cells in the immune system, like an identity parade. Our cells have a truly astonishing range of abilities to recognise different protein structures, and there will be some which recognise...

...each of the pieces of the invader. The cells which recognise a piece are instructed to multiply selectively so that, after a few days to a couple of weeks, our bodies contain large numbers of virus piece specific cells. These have a range of functions. Some make antibodies...