Today I Learned

[pbuk]

You do not need a hack to display [/PLAIN]. In the absence of a [PLAIN] opening tag, the closing tag will not render and will be displayed verbatim instead.

Yes, I was thinking of the situation where there were both opening and closing [PLAIN][/PLAIN] tags (the opening tag would work but the closing tag wouldn't). @mfb provides an improvement on the colour hack, there is also [[plain]PLAIN][[/plain]/PLAIN].

 

[mfb]

That will break if there is more than one section of $\LaTeX$ as MathJax will try to process the text between the two unobfuscated tags.

Sure, all but one tags need to be broken up.

 

[Orodruin]

Matlab actually has object orientation ...

 

[fresh_42]

O.k., do not travel with Tom Hanks. Obviously. But TIL that flying XY191 is dangerous, too!
https://en.wikipedia.org/wiki/Flight_191

 

[ridgerunner]

Today I learned the PF implementation of LaTex/MathJax!

Because of this cool PF feature, (i.e. pretty-printing Math formulae), I decided to go ahead and join up today, (and donate enough to become a lifetime Gold Member). Reason being; I need a place to publish my recently developed derivation of a set of force and power equations which describe the behavior of an idealized DDWFTTW cart operating at and beyond wind speed. (These derivations utilize the same assumptions, nomenclature and fundamental Newtonian Mechanics principles as those used to derive the WikiPedia Betz Law proof.)

e.g. The following equation defines the net force acting on the cart, where: $\rho$ is the fluid density in kg/m³, $S$ is the swept area of the rotor disc in m², $V_{wind}$ is the velocity of the air in the ground reference frame in m/s, $n$ is the dimensionless cart speed ($n = \frac {V_{cart}} {V_{wind}}$), and $\Delta$ is the dimensionless change in velocity of the air passing through the propeller's control volume ($\Delta = \frac {V_2 - V_1} {V_{wind}}$):
$$\left[ F_{net} = \frac 1 2 \rho S V_{wind}^2~*~ \frac 1 n \left\{-\frac 1 2 \Delta^3 + (2 - n) \Delta^2 + (2 n - 2) \Delta \right\} \right]_{\rm{14c.}}$$
Stay Tuned!
(p.s. This is my first post. In the immortal words of Dr. Nick: Hi, Everybody!

 

[berkeman]

Reason being; I need a place to publish my recently developed derivation of a set of force and power equations which describe the behavior of an idealized DDWFTTW cart operating at and beyond wind speed.

Welcome to PF. We don't allow self-publishing your work here (it needs to be published in a reputable peer-reviewed journal first), but we do have several threads about the DDWFTTW subject that you should be able to participate in. Send me a Private Message (PM) if you have trouble finding those existing threads.

 

[ridgerunner]

...
$$\left[ F_{net} = \frac 1 2 \rho S V_{wind}^2~*~ \frac 1 n \left\{-\frac 1 2 \Delta^3 + (2 - n) \Delta^2 + (2 n - 2) \Delta \right\} \right]_{\rm{14c.}}$$
Stay Tuned!
(p.s. This is my first post. In the immortal words of Dr. Nick: Hi, Everybody!

Welcome to PF. We don't allow self-publishing your work here (it needs to be published in a reputable peer-reviewed journal first), but we do have several threads about the DDWFTTW subject that you should be able to participate in. Send me a Private Message (PM) if you have trouble finding those existing threads.

Are you saying that the only equations/derivations that should be posted here are those that have been previously published in peer reviewed scientific journals? That makes no sense! When I joined up yesterday, I assumed that freely discussing physics is what this forum was all about. I was simply hoping to publish... post my derivations here, (using the clean mathematical presentation tools you provide), to elicit critical feedback from your community. I would think that you would be happy to receive and discuss new, unproven ideas in addition to known, well established science. Am I wrong?

p.s. I am aware of, (and have thoroughly read), most of the DDWFTTW related threads here on PF, (as well as many other locations across the internet), as I have been closely following this subject for more than a dozen years.

 

[hmmm27]

I think this is the most recent...

 

[PeterDonis]

I would think that you would be happy to receive and discuss new, unproven ideas in addition to known, well established science. Am I wrong?

Yes. We don't allow discussion of personal research and personal theories here because we have found, through bitter experience with trying such things in the past, that it doesn't work; nothing worthwhile ever comes out of it and it becomes a huge nightmare of threads with invalid content in them and unending arguments.

When I joined up yesterday, I assumed that freely discussing physics is what this forum was all about.

The primary purpose of PF is to help people understand physics that is already mainstream. We do have some forums, such as the QM interpretations subforum and the Beyond the Standard Model forum, where we have discussion of work that is not yet mainstream (because there are no mainstream theories or interpretations in those areas, at least not yet), but even there discussion should be based on published research, not on the personal research or theories of members.

 

[strangerep]

TIL... courtesy of Dilbert (actually, Catbert), that whisker fatigue is a real thing.

 

[Rive]

whisker fatigue is a real thing.

Well. Should we redefine 'tickling' as 'skin fatigue', then?

 

[anorlunda]

LOL Old school triumphed today.

I've been having trouble with the AC in my RV. I called for a repairman and told him that I thought a relay contact was stuck closed.

The guy came, and started running tests and making measurements. He just graduated from AC technician school this year. He was surprised that the AC is 21 years old. He said new ones only last 5-6 years. When he got into the control board, there sat a big black relay. He was thinking of replacing the relay or finding a replacment board. My wife said, "Hell, just whack it." The repairman looked stunned. But we convinced him. He whacked it with a rubber mallet and now everything works fine again. I spent $50 on his call instead of $1000 for a new AC of inferior quality.

He shook his head and said, "My buddies won't believe me when I tell them I fixed it with a mallet."

You see my wife remembers our first car. It had a sticky relay in the voltage regulator. She knew that when the voltage went high, that she should fetch the tire iron and give the regulator a firm whack. That worked for the lifetime of that car.

Old school. It worked then, and it can still work today in the right circumstances.

 

[Tom.G]

I spent $50 on his call...

...because I didn't ask my wife first!
(been there... )

 

[pinball1970]

LOL Old school triumphed today.

I've been having trouble with the AC in my RV. I called for a repairman and told him that I thought a relay contact was stuck closed.

The guy came, and started running tests and making measurements. He just graduated from AC technician school this year. He was surprised that the AC is 21 years old. He said new ones only last 5-6 years. When he got into the control board, there sat a big black relay. He was thinking of replacing the relay or finding a replacment board. My wife said, "Hell, just whack it." The repairman looked stunned. But we convinced him. He whacked it with a rubber mallet and now everything works fine again. I spent $50 on his call instead of $1000 for a new AC of inferior quality.

He shook his head and said, "My buddies won't believe me when I tell them I fixed it with a mallet."

View attachment 316904

You see my wife remembers our first car. It had a sticky relay in the voltage regulator. She knew that when the voltage went high, that she should fetch the tire iron and give the regulator a firm whack. That worked for the lifetime of that car.

Old school. It worked then, and it can still work today in the right circumstances.

Reminded of….

 

[Rive]

My wife said, "Hell, just whack it."

I guess that may hint some ... 'consultation fee' ... especially in account of that $950 saved

 

[anorlunda]

By the way, I owe my career to a faulty relay .

The Great Northeast Blackout of November 9, 1965 launched my career as a power engineer. The investigation showed that the triggering event was caused by a moth in a relay at the Sir Adam Beck power plant in Ontario.

 

[jack action]

By the way, I owe my career to a faulty relay .

The Great Northeast Blackout of November 9, 1965 launched my career as a power engineer. The investigation showed that the triggering event was caused by a moth in a relay at the Sir Adam Beck power plant in Ontario.
View attachment 316926

Haaa! the famous "bug":

The term "bug" was used in an account by computer pioneer Grace Hopper, who publicized the cause of a malfunction in an early electromechanical computer. A typical version of the story is:

In 1946, when Hopper was released from active duty, she joined the Harvard Faculty at the Computation Laboratory where she continued her work on the Mark II and Mark III. Operators traced an error in the Mark II to a moth trapped in a relay, coining the term bug. This bug was carefully removed and taped to the log book. Stemming from the first bug, today we call errors or glitches in a program a bug.

 

[anorlunda]

Haaa! the famous "bug":

Her's was the first of a long line of notable bugs.

 

[BillTre]

 

[anorlunda]

5200 Drone light show, Breaking 4 World Records -- High Great​

What fun it would be to write the software.

 

[kyphysics]

I learned that if one particle of dust is introduced onto a silicon wafer, during production process, the whole batch can be at risk of being ruined. Creating a microchip from silicon is a very, very meticulous process demanding extreme precision and care.

It takes an average of 12 weeks to make one of these chips. Who knew. . .

 

[jack action]

I learned that if one particle of dust is introduced onto a silicon wafer, during production process, the whole batch can be at risk of being ruined. Creating a microchip from silicon is a very, very meticulous process demanding extreme precision and care.

It takes an average of 12 weeks to make one of these chips. Who knew. . .

And then you learned about the fascinating story of how this guy did one at home, something experts thought was impossible:

​

More info on his website: http://sam.zeloof.xyz/first-ic/

 

[berkeman]

I learned that if one particle of dust is introduced onto a silicon wafer, during production process, the whole batch can be at risk of being ruined.

And then you learned about the fascinating story of how this guy did one at home, something experts thought was impossible:

Yeah, but way different feature sizes.

It's no fun getting into a bunny suit to go into a fab to debug machine problems (especially if you have to bring your instruments with you)...

 

[BillTre]

 

[BillTre]

 

[pinball1970]

TIL (the other week but just got round to it) UK flu vaccine is quadrivalent. 2x A and 2x B strains.

 

[kyphysics]

Amazon is gutting its voice-assistant Alexa. Employees describe a division in crisis and huge losses on 'a wasted opportunity.'​

https://www.businessinsider.com/amazon-alexa-job-layoffs-rise-and-fall-2022-11

So, no futuristic A.I. voice/bot assistant in every U.S. home on the horizon? And I thought we were getting closer and closer to Star Trek living.

I also didn't know Alexa was behind Google Assistant and Apple Siri in use/popularity.

 

[Hornbein]

Amazon is gutting its voice-assistant Alexa. Employees describe a division in crisis and huge losses on 'a wasted opportunity.'​

https://www.businessinsider.com/amazon-alexa-job-layoffs-rise-and-fall-2022-11

So, no futuristic A.I. voice/bot assistant in every U.S. home on the horizon? And I thought we were getting closer and closer to Star Trek living.

I also didn't know Alexa was behind Google Assistant and Apple Siri in use/popularity.

I tried. I was told the site was unsafe, then the whole thing went into an infinite loop.

 

[Orodruin]

Today I found this out …

 

[fresh_42]

Today I found this out …
View attachment 317508

If we meet, then LIGO can make a measurement.