Today I Learned
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Mentor
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Salmonella has nothing to do with salmon, it was named after Daniel Salmon. By Joseph Lignières, after Theobald Smith discovered it.
Adesh
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Today I learned that not all little brats fear this insect
I must devise some new ways for controlling those naughty little demons.
I must devise some new ways for controlling those naughty little demons.
Jonathan Scott
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Today I learned to be more careful when taking powers of matrices. I had used the following:
$$\begin{bmatrix}
a & 0 \\
0 & 0
\end{bmatrix} ^ n
=
\begin{bmatrix}
a^n & 0 \\
0 & 0
\end{bmatrix}
$$
... but I got an unexpected result for a case which included ##n = 0##, because any matrix to the power zero should be the identity matrix. My daughter kindly pointed out a more generally correct identity as follows:
$$\begin{bmatrix}
a & 0 \\
0 & 0
\end{bmatrix} ^ n
=
\begin{bmatrix}
a^n & 0 \\
0 & 0^n
\end{bmatrix}
$$
The term ##0^n## then correctly gives the identity matrix when ##n=0##, assuming ##0^0 = 1##, and gives the same overall result as I had expected using my usual (Clifford Algebra) method of calculation.
$$\begin{bmatrix}
a & 0 \\
0 & 0
\end{bmatrix} ^ n
=
\begin{bmatrix}
a^n & 0 \\
0 & 0
\end{bmatrix}
$$
... but I got an unexpected result for a case which included ##n = 0##, because any matrix to the power zero should be the identity matrix. My daughter kindly pointed out a more generally correct identity as follows:
$$\begin{bmatrix}
a & 0 \\
0 & 0
\end{bmatrix} ^ n
=
\begin{bmatrix}
a^n & 0 \\
0 & 0^n
\end{bmatrix}
$$
The term ##0^n## then correctly gives the identity matrix when ##n=0##, assuming ##0^0 = 1##, and gives the same overall result as I had expected using my usual (Clifford Algebra) method of calculation.
Klystron
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Teach it to smoke a tiny hookah while sitting on a mushroom. You can discuss the nature of reality.Adesh said:
Reference: "Alice's Adventures in Wonderland" by Lewis Carroll.
Adesh
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To be honest I didn’t get your joke, I laughed because I was certain that it was a joke.Klystron said:
Klystron
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Hence the reference to "Alice in Wonderland". Perhaps I am mistaken but I took your insect to be a caterpillar, the larval stage of moths and butterflies. After several confusing geometric adventures, tiny Alice encounters a hookah smoking caterpillar sitting on a mushroom.Adesh said:
"Who Are You?", the Caterpillar asks Alice, puffing blue smoke in her face.
hmmm27
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It's a caterpillar... one of the more cool looking ones (Monarch ?)... I don't think anybody's ever been afraid of them.
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Looks like pine processionary.hmmm27 said:
Adesh
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I think almost every girl fear them. Just take it close to them and they will **YELL**. Earlier some kids too fear that.hmmm27 said:
Adesh
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Yes, I too think so.fresh_42 said:
Hsopitalist
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fresh_42 said:
Omg, I literally just noticed your username...
etotheipi
TIL unit vectors are unitless
Last edited by a moderator:
DennisN
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Today I learned that computer science is not the field with most abbreviations/acronyms.
I tried to read this paper a while ago (related to coronaviruses) and I pretty quickly understood I would have no chance of understanding it. At all
. It is full of words and concepts I've never heard of, combined with an avalance of weird abbreviations that seems to laugh at me; "haha, you'll never understand what this means."
Gosh, that paper is utterly incomprehensible to me.
I tried to read this paper a while ago (related to coronaviruses) and I pretty quickly understood I would have no chance of understanding it. At all
. It is full of words and concepts I've never heard of, combined with an avalance of weird abbreviations that seems to laugh at me; "haha, you'll never understand what this means."Gosh, that paper is utterly incomprehensible to me.
Science Advisor
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While many of the abbreviations in the paper were defined (usually in parentheses following the words they stand for), using so may can be off-putting even to a biologist.
There are others in there that are names of things, but look like an abbreviation (such as NL63, the name of a particular human coronavirus). In some cases the names may have some acronymic basis (perhaps NL63 was the 63rd human Coronavirus found in a National Lab), but now they might just be considered to be names. I have named antibodies in a similar way.
Regardless, this paper is intended for a specialized professional audience who are motivated to wade through the letters to get to the meaning and are already familiar with the underlying concepts.
Personally, I don't like papers with a lot of abbreviations like this. They are a pain to work through.
Sometimes papers are written this way to get an article under the page limits on the length of an article that a journal will accept. Several of those abbreviations could be written out without any loss of readability. Replacing others might not help readability at all. Names of the culturing media RPMI 1640 would not be made more understandable if RPMI is known to mean Roswell Park Memorial Institute.
Some things are like star names/numbers.
Biology/molecular biology has a lot of them.
Humans have 20,000-30,000 protein coding genes and ~4 billion base pairs. They all can be named.
There are others in there that are names of things, but look like an abbreviation (such as NL63, the name of a particular human coronavirus). In some cases the names may have some acronymic basis (perhaps NL63 was the 63rd human Coronavirus found in a National Lab), but now they might just be considered to be names. I have named antibodies in a similar way.
Regardless, this paper is intended for a specialized professional audience who are motivated to wade through the letters to get to the meaning and are already familiar with the underlying concepts.
Personally, I don't like papers with a lot of abbreviations like this. They are a pain to work through.
Sometimes papers are written this way to get an article under the page limits on the length of an article that a journal will accept. Several of those abbreviations could be written out without any loss of readability. Replacing others might not help readability at all. Names of the culturing media RPMI 1640 would not be made more understandable if RPMI is known to mean Roswell Park Memorial Institute.
Some things are like star names/numbers.
Biology/molecular biology has a lot of them.
Humans have 20,000-30,000 protein coding genes and ~4 billion base pairs. They all can be named.
Science Advisor
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That means a sample of half the the people in the world could be named without a name duplication... astonishing!BillTre said:
Using the 52 upper & lower case letters of the English alphabet the names would be around 200 000 characters long, quite a dictionary.
Science Advisor
Homework Helper
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TIL that Google has limits; "tasmania"+"wave cut beaches" equals absolutely zero information regarding emergent coastlines vs. submergent coastlines. There are remarks about beaches as far as 200 feet/60 m above current sea level. Cable screen-saver showed me pictures and subsequent search for what I'd taken for granted as a rather dull tectonic history of Oz yielded bupkus.
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Today I learned that it is Thursday!
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Science Advisor
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I was catching up on this thread just now, with my iPOD playing in the background. Just as I read this post:
Is there a word for that coincidence? When you are reading and someone speaks the word as you read it? It seems to happen often.
Just then the Airplane song was playing and in fact Grace Slick sang "hookah" as I read the word on the screen.Klystron said:
Is there a word for that coincidence? When you are reading and someone speaks the word as you read it? It seems to happen often.
Klystron
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Serendipity. These confluences of ideas occur so often one can almost believe they are connected; information linked; things occur just out of sight in brief glimpses.gmax137 said:
Hsopitalist
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gmax137 said:
Oh no, did he just bring up a probability concept?
Lisa!
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Today I learned from PF that we can say
This poll will close: Tomorrow at 7:53 PM.
This poll will close: Tomorrow at 7:53 PM.
GiriBang
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Hiragana (Basic Japanese alphabets)
Klystron
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Today I learned (once again) that physics reuses acronyms.
Now I always realized that I learned electronics at a young age when vacuum tubes were high tech from many old textbooks and papers and that my knowledge was pragmatic and practical from many years experience with RF. My somewhat geometrical understanding of electromagnetic fields (emf) serves me well, seems to agree with observations and most experts on these forums and I do not try to teach my personal approach in keeping with PF policy. No trouble understanding modern circuits.
Today I learned that some people intend emf as an acronym for electromotive force and regard this force (?), not electromagnetic fields, as central to understanding electronics. Of course, I am familiar with classical concepts and also understand modern teachers deconstruct electric and magnetic fields as an aid to understanding both.
I feel strange, as if I have journeyed too far from home.
Now I always realized that I learned electronics at a young age when vacuum tubes were high tech from many old textbooks and papers and that my knowledge was pragmatic and practical from many years experience with RF. My somewhat geometrical understanding of electromagnetic fields (emf) serves me well, seems to agree with observations and most experts on these forums and I do not try to teach my personal approach in keeping with PF policy. No trouble understanding modern circuits.
Today I learned that some people intend emf as an acronym for electromotive force and regard this force (?), not electromagnetic fields, as central to understanding electronics. Of course, I am familiar with classical concepts and also understand modern teachers deconstruct electric and magnetic fields as an aid to understanding both.
I feel strange, as if I have journeyed too far from home.
Homework Helper
Education Advisor
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Google will let you graph two functions of a single variable if a comma separates each function.
Admin
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TIL to avoid cough medicines that contain dextromethorphan (very common apparently), at least until you get your SARS-CoV-2 vaccination...
https://www.kqed.org/science/1963298/common-ingredient-in-common-cough-medicine-might-promote-coronavirus-study-finds
jim mcnamara said:
berkeman said:Looks to be pretty common. It's in both of the cough medicines we had in our cabinet. Guess we'll set these aside until we get vaccinated next month...
View attachment 262289
https://www.kqed.org/science/1963298/common-ingredient-in-common-cough-medicine-might-promote-coronavirus-study-finds
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I swear on fir syrup, and codeine in case I have tickets for the opera, but never ever in any other case. Dextromethorphan sounds to be a no-go, when I read the list of potential side effects and contraindications.berkeman said:
Science Advisor
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Humid air is lighter than dry air!
I'd never really thought about it, so it seemed obvious that adding water to air would make it heavier. Then, it was even more obvious that it is true once you think about the molecular weights. Very counter intuitive - Science FTW!
https://phys.org/news/2020-05-cold-air-riseswhat-earth-climate.html
I'd never really thought about it, so it seemed obvious that adding water to air would make it heavier. Then, it was even more obvious that it is true once you think about the molecular weights. Very counter intuitive - Science FTW!
https://phys.org/news/2020-05-cold-air-riseswhat-earth-climate.html