The h Bar

DanielSank

17:00

Oh, it's moldy blue cheese.

Gross.

Sir Cumference

@JohnRennie Smoked mozzarella does tho

John Rennie

@DanielSank it's very strong, very sharp and veeeeery smelly :-)

DanielSank

I like strong, but not moldy.

Moldy food is gross.

John Rennie

Bread?

Beer?

Yeast are fungi

DanielSank

Neither of those involves mold.

Yeast are fungi. Mold are fungi. Yeast are not mold.

Also, I do not particularly like yeast in my fermented beverages.

John Rennie

17:02

Oh well

DanielSank

It's best to get as much out as possible. Yeast tastes kinda bleh.

This reminds me that I need to make more hooch...

Anonymous

@SirCumference Spicy mozzarella is good

Anonymous

If well made/marinated

vzn

@called2voyage seems to be related to QM + GR unification, early experimental steps. there are some new theories that consider gravity to be a distortion of the spacetime fabric, along with light (photons). the article/ research expresses it all from a particle-centric pov (excitons + polaritons etc).

Anonymous

17:21

Is there any reason why wireless internet seems to slow down on rainy days? Based on my observation it seems to be true

ACuriousMind

@Blue The bytes stop on their way to smell the rain.

Anonymous

There are some answers here and there on the net, but I'm not sure they're authoritative enough

Anonymous

@ACuriousMind Lol. It's a serious question tho :P

Anonymous

I'd like to know the answer

ACuriousMind

If this is a real phenomenon (I can't say I've noticed it) that would make a good question for our site, actually

Anonymous

17:24

I think I'll post it :) Lemme collect some evidence first over a couple of days

Anonymous

I'll post the net speed results along with the weather variation

DanielSank

@Blue More people at home watching movies.

@ACuriousMind Nah, it's probably social more than physical.

ACuriousMind

@Blue Wait, is the WiFi slower or the internet?

DanielSank

You'd have to measure the difference in data rate for wired and wireless connections to the same modem.

Anonymous

@DanielSank Hmm, but my wired net connection's speed doesn't seem to drop

Anonymous

17:29

Only the mobile net connection

DanielSank

@Blue OH! You're talking about LTE?

Anonymous

@DanielSank Right

DanielSank

Are you talking about WiFi or LTE/GSM/etc.

Anonymous

4G

DanielSank

ah

Ok that actually does make sense, maybe.

At 4 GHz it might just be loss in the water.

vzn

17:32

@Blue had that same problem once. it turned out to be a real (physics-related) issue. the insulation was wearing out on a ground wire and the weather/ precipitation/ moisture had a major effect on signal-to-noise ratio (ie electrical conduction). an unfortunate telephone employee came out in the middle of the winter with snow out and dug up the ground to replace the wire.

DanielSank

Yeah, it might be just dielectric loss in the water.

Remember, microwave ovens operate at ~2.5 GHz and work by heating up water :-)

Anonymous

@DanielSank I think so. It would be interesting to see the actual math of which frequencies get lost

DanielSank

@Blue !!??!?!?!

You want math showing why water absorbs at certain frequencies? That's kind of a big calculation.

ACuriousMind

Math? I think in this case just doing an experiment and measuring the loss would be the way to go, no?

DanielSank

^

Anonymous

17:36

@ACuriousMind Has such an experiment been done? Must have been, but I'm not very aware

Novalium Company

Evening

ACuriousMind

I'm sure someone somewhere has measured water's absorbance for a multitude of frequencies

DanielSank

@Blue You can look up water's dielectric constant vs. frequency in two seconds on the internet :-0

Novalium Company

Guys, I asked @JohnRennie this question before, he explained it to me, but now something popped up. Does someone know a fridge works?

DanielSank

What kind of fridge?

Novalium Company

17:38

home refrigerator

DanielSank

Have you looked up anything online?

Novalium Company

I know how it works, but my question is about how pressure and temperature are related.

DanielSank

It comes down to expansion of a coolant, but why that causes cooling requires either some thermodynamic theory, or thinking carefully about atoms.

Lozansky

Something something Carnot cycle

DanielSank

@NovaliumCompany Ok, so maybe ask your specific question so we don't have to guess what you want to know :-)

Novalium Company

17:43

So the fridge is working on the principles: First air from the room gets sucked up through a pump and gets compressed, now we have high pressure, high temp. air, after that this air goes to a radiator where it's temp. gets lower, and we have a high pressure, room temperature air, then it goes into an expansion chamber where the pressure is used to lower the temperature below the room temp. My question is that I thought pressure and temp. are related?

@DanielSank Well?

Anonymous

@DanielSank I could, yes. But there are a lot more aspects of it I'm concerned about. For instance, can we calculate by how much the net speed slows down for a certain amount of precipitation? Does the settling down of dust particles and wind also have an effect on the speed?

ACuriousMind

@NovaliumCompany Are you asking why the cooling to room temperature doesn't return the fluid (fridges generally don't use air but a fluid refrigerant) to its initial pressure?

Novalium Company

I'm asking: @JohnRennie Told me that pressure and temperature are related, so how can we have high pressure and low temperature (in the radiator)

ACuriousMind

@NovaliumCompany Well, they are "related" in that increasing or descreasing one generally increases or decreases the other one, too. What exactly is the question about that?

If you start at a certain pressure and temperature, then lowering the temperature will lower the pressure, but it depends on the material you're cooling by how much

Novalium Company

In the radiator, high pressure, high temp, fluid enters, thermal equilibrium occurs and we get a high pressure, low temp. fluid, wtf? Shouldn't it be low pressure, low temp fluid, since they are related?

enumaris

17:51

you could decrease the volume

Novalium Company

well?

Anonymous

@NovaliumCompany Temperature isn't the only factor pressure depends on

enumaris

not familiar with how radiators work

DanielSank

@Blue Dude.

Novalium Company

My question is: If pressure and tempearature are related, then in a radiator, when a high temperature, high pressure enter, how a high pressure, low temperature leave?

DanielSank

17:57

You're getting into the encodings used for WiFi and how their data rate depends on signal to noise ratio.

Also things like whether or not the WiFi router can increase its output level if it detects loss between the transmitter and the computer.

ACuriousMind

@NovaliumCompany Well, you're missing the part where the refrigerant switches from gaseous to fluid. It works like this: You start by compressing the gas, which is then passed as a hot, high-pressure gas into the condenser, which is in thermal contact with the room air. There the gas cools, and becomes fluid as it does.

The fluid builds up behind a valve into the evaporator, which is at low pressure. When the fridge needs to be cooled, the valve is opened, and some of the fluid is sucked into the evaporator. Because of the low pressure, it expands rapidly, some of it evaporates, and the fluid-gas mixture cools because of the evaporation heat.

The main cooling action is really because of the fluid->gaseous switch, and not any relation between pressure and temperature

Anonymous

@DanielSank Yes, I suppose. I'd be interested to learn that in greater depth to explain this phenomenon

Anonymous

I'm sure this is quite a mainstream topic. Just that I'm not well equipped with the relevant details

Anonymous

But thanks

Anonymous

We have this stuff in our third year I think

Anonymous

18:02

In microwave engineering and electromagnetic waves

Anonymous

and those communications engineering stuff

ACuriousMind

I should add that the phase change is not a requirement for the refrigeration cycle to work, though. It's just more efficient that way.

Anonymous

18:23

@ACuriousMind C hulp needed! Any idea what UINT64_C(2685821657736338717) stand for, here?

Anonymous

Line 36

Anonymous

and 44

Anonymous

I haven't come across that thing before

Anonymous

Actually haven't used any uint64 stuff before

ACuriousMind

@Blue It's a type cast

i.e. the literal in brackets is being cast to UINT64_C

Anonymous

18:29

But how did that number 2685821657736338717 appear all of a sudden?

Anonymous

The programmer wrote it down randomly?

Anonymous

I'm trying to decipher the code

ACuriousMind

Well, yes. This is why named constants are better than literals - a meaningfully named constant would've told you why its there.

Anonymous

I see. They seem to be trying to generate random numbers using some bitwise operations

ACuriousMind

The comment tells you the prng algorithm used is xorshift64, though. Have you looked at an explanation of said algorithm for whether this magic number appears there?

enumaris

18:34

it's probably some period or something...?

ACuriousMind

In particular, this algorithm is what Wiki knows as xorshift*

Anonymous

@ACuriousMind Ah, I'm reading it now. Just found it on wiki

ACuriousMind

How the programmer came up with your specific value of the multiplication constant is anyone's guess, though.

enumaris

it's in the wikipedia lol

but as hexidecimal

return x * 0x2545F4914F6CDD1D;

in the xorshift* section

ACuriousMind

I can't read Hex in my head, is that the same as the decimal literal in Blue's code?

enumaris

18:37

I think so

wolframalpha.com/input/?i=0x2545F4914F6CDD1D+in+decimal

I didn't verify every digit, only the first 4 or 5

Anonymous

@ACuriousMind You try so hard to pass the Turing test :P

Anonymous

2685821657736338717

Anonymous

vs the one in code: 2685821657736338717

Anonymous

So yes

ACuriousMind

Mystery solved, then

Lozansky

18:39

Amazing how far AI has come

Abcd

@skull Whats the reason?

Anonymous

@Lozansky Yeah, it even tries to prove that it isn't AI

Anonymous

@ACuriousMind Yep, thanks :)

skull

@Abcd don't know, they always keep it private

Sid

@skull I don't think mods are allowed to talk about suspensions in public.

Anonymous

18:48

@ACuriousMind In the prng_u64_less(void) what's the problem if result = UINT64_C(18446744073709551615)? I don't understand the use of that function

Anonymous

18446744073709551615 doesn't seem to be given in the standard algo

Abcd

@Blue or @Sid can you please visit the maths room?

ACuriousMind

@Blue Have you looked at what that value is in hex? ;)

Anonymous

ffffffffffffff..._16 (16 digits)

ACuriousMind

@Blue Well...that's the first WA output but not the most helpful ;) If you go down to the "other data types" section and click on "more", you should see that it's precisely the maximal integer that fits into a 64-bit int.

Sid

18:52

@Abcd I am sorry, I am working on something right now. I will see later.

Abcd

Ok

ACuriousMind

I.e. whoever wrote that code didn't want to return maxint, basically

Anonymous

@ACuriousMind But why though? Maybe I'll understand when I read the rest of the code

Anonymous

Overflow perhaps?

ACuriousMind

Oh god it uses the --> operator

run away from that code, now :P

Anonymous

18:58

Heh, I never saw anyone use that operator before

Captain Bohemian

why is Stack Overflow taken as the name of a site for talking about programming?

ACuriousMind

@CaptainBohemian Because a stack overflow is a common error in programming

@Blue It's not really an operator. It's also kinda infamous on SO, see stackoverflow.com/q/1642028/3929857

Who gave you this code?

enumaris

@Blue that's 2^64-1 which is the period of a 64 bit PRNG

Anonymous

@ACuriousMind The user Nominal Animal on Stack Overflow. He was helping me with a project over mail. Normally it takes me hours to understand his weird coding style

Captain Bohemian

@ACuriousMind really? But outsiders can't understand what it is if there is no explanation

enumaris

19:03

looks like ACM already figured it out

cool beans

Anonymous

You can control speed with an arrow!

int x = 100;

while( 0 <-------------------- x )
{
printf("%d ", x);
}

Anonymous

Lol

Anonymous

This looks fun

Sid

@Blue ....ew

That has to be one of the worst codes I have ever seen.

Anonymous

It's the best for me

ACuriousMind

19:12

@Sid You ain't seen nothing yet

enumaris

ughhhhh

Lozansky

You are allowed to move around torques in a rigid body, right?

Anonymous

@Lozansky Depends on what type of torque

Anonymous

You can translate moments if they're couples

Lozansky

@Blue Yes, but not point moments right?

Anonymous

19:19

Yep

Lozansky

@Blue Do you know how to find $\sigma_x, \sigma_y$ when you have a rotated planar sheet like this?

And I guess I want the strain $\tau_{xy}$ as well

Anonymous

19:39

Explain your symbols man

Lozansky

$\sigma$ is stress, $\tau$ is strain. I assume elastic material so Hooke's law and Mohr's circle can be applied

Anonymous

Stress is force per unit area. What's your force? What's your area?

Lozansky

You don't need that to find $\sigma_x, \sigma_y, \tau_{xy}$?

It's like Cauchy's stress tensor but in a rotated coordinate system

And I want to go back to good ol'e $x,y$

Anonymous

Okay, but we atleast need some information about the material. How can you say what the stresses are without any information about the material?

Lozansky

You apply $\sigma(\varphi) = \sigma_x \cos^2 \varphi + \sigma_y \sin^2 \varphi + 2 \tau_{xy} \sin \varphi \cos \varphi$

Anonymous

19:48

You want to leave it in that form?

Lozansky

No no, I want to find $\sigma_x, \sigma_y, \tau_{xy}$

It's easy if you are given $\epsilon_i$ for $i=1,2,3$ with given $\varphi_i$

And then using Hooke's generalized law to find the stresses

Anonymous

Maybe you're looking for this?

Anonymous

I'm not very knowledgeable about continuum mechanics, sorry

Lozansky

@Blue Ah yes, then $\sigma_x = \sigma \cos^2 \varphi, \sigma_y = \sigma \sin^2 \varphi$

If I'm reading that correctly

Novalium Company

20:08

Guys, do you need high voltage and low current to produce a spark or low voltage and high current?

enumaris

a spark is generally high voltage and low current

but you could do high voltage and high current

just bigger spark

Novalium Company

yep, got that, thanks

Actually, you don't actually need current to produce a spark, do you?

enumaris

to make a spark you have to have high enough voltage to breakdown the dielectric (air). The dielectric breakdown of air is roughly about 3*10^6V/m so to make a spark 1cm long you need voltage of ~30,000 Volts

Anonymous

Yeah, just a high voltage will do

enumaris

You need at least some current, since the spark itself is a current of electricy

but you could have a tiny spark with minimal current I guess

like static electricity -> spark but the spark is a small "current"

Novalium Company

20:12

Ok got it. So if I have a 9V battery, I can convert some of the current into more voltage with a transformer right?

ACuriousMind

@NovaliumCompany Transformers only work with AC.

enumaris

You need a boost converter: en.wikipedia.org/wiki/Boost_converter

Novalium Company

Oh yep, makes sense, Faraday's law, duhh. :D So is there a dc transformer or something?

enumaris

see my link

Novalium Company

@enumaris thanks.

enumaris

20:15

np

Anonymous

@NovaliumCompany That's.....not what a transformer does

Novalium Company

It works on Faraday's principle, doesn't it?

Anonymous

It steps up or steps down voltage

Novalium Company

Yep.

Anonymous

"So if I have a 9V battery, I can convert some of the current into more voltage with a transformer right?"

Anonymous

20:17

What do you mean by that?

Novalium Company

Well, I forgot that transfomers are only for ac.

Anonymous

Leaving that part

Anonymous

Take an AC voltage

Anonymous

$9\sin(\omega t) V$

Anonymous

It still doesn't make sense

Novalium Company

20:18

I haven't studied Ac yet ;\

Anonymous

Transformer doesn't convert current to voltage

Novalium Company

All I know is that it's alternating current in the form of a wave?

Anonymous

@NovaliumCompany You don't need to

Novalium Company

So the transformer affects only voltage, but not current?

So I can step down or step up $only$ voltage?

Anonymous

Well, if you step up voltage, current will be stepped down

Anonymous

20:19

$V\times I$ is the power

Anonymous

Which should ideally be constant

Novalium Company

Yep, so the power stays the same.

Anonymous

Hmm, but I still don't get what you meant by: " I can convert some of the current into more voltage with a transformer right?"

Anonymous

Did you actually mean step down current to step up voltage?

Novalium Company

Exactly.

P = IV, where P is a constant, so I will get smaller and V will get bigger.

Anonymous

20:23

Okay, cool then

Novalium Company

4 weeks (or less) and I am off school YAAY

gateprep

Why is engineering strain even required?

I tried SE but could understand nothing

Someone pls answer in a simple language..

enumaris

weez

ACuriousMind

@gateprep required for what?

gateprep

GATE

enumaris

20:30

wat

ACuriousMind

If that's an acronym, I have no idea what it stands for

Anonymous

@gateprep Maybe this and this will help?

ACuriousMind

But I guess if it is some sort of exam, it at least explains your name :P

gateprep

@ACuriousMind You are correct..Tell me something why do we not take true stress when that is even more accurate.

Anonymous

@ACuriousMind Yeah, it is

Anonymous

20:33

@gateprep It's not a matter of accuracy. They tell us different informations about the material

gateprep

thats right but why did we plan to bring in engineering strain then?

Anonymous

Read this: john.maloney.org/Papers/On%20strain%20(9-20-06).pdf

Anonymous

Page 2

Anonymous

Last para

gateprep

Thanks@Blue for being so responsive....I am sure you will help me further in future....

@Blue

Btw I am frim JU as well dudue

Hollah!!

Anonymous

20:40

@gateprep I'm not well versed in mechanical engineering topics, but I'll try when I can

Anonymous

@gateprep Nice, which department and year?

gateprep

Yes pls do...

3rd yr department secret one among chemical,civil and metallurgy..

U from ECE..

Anonymous

Surely not chemical, lol

Anonymous

You wouldn't be asking such questions then

Anonymous

I guess metallurgy

Anonymous

20:42

@gateprep Yes

Anonymous

@gateprep Good to know

gateprep

yr?

Anonymous

1st year

gateprep

@Blue ohh great...When is the univ reponening

?

Anonymous

No idea

Anonymous

20:44

They'll update on the website I suppose

Anonymous

Probably July end or August

gateprep

is the yield point which when reached will result in a permanent deformation of an arbitrarily defined amount of strain (sometimes 0.2%) when the stress is removed.

I dont get point c!!@Blue

0

Q: Yield Point and Elastic Limit

Elastic Limit - the point upto which the wire reatins its original length after the force is withdrawn. Yield Point - The point where there is a large permanent change in length with no extra load force. These are how these two are defined in my A Level book and also stated by my teacher. In W...

pls answer

Anonymous

Yield (engineering)

The yield point is the point on a stress–strain curve that indicates the limit of elastic behavior and the beginning of plastic behavior. Yielding means the start of breaking of fibers. Yield strength or yield stress is the material property defined as the stress at which a material begins to deform plastically whereas yield point is the point where nonlinear (elastic + plastic) deformation begins. Prior to the yield point the material will deform elastically and will return to its original shape when the applied stress is removed. Once the yield point is passed, some fraction of the deformation...

Anonymous

Gotta go now. Sorry.

Anonymous

Cya

enumaris

20:50

wikipedia is your friend

gateprep

bye

Emilio Pisanty

22:58

@DanielSank that appears to be caused by your use of some weird non-standard definition of "good food"

Food in Barcelona is awesome

All that pork and salted pork =D

enumaris

iberian pork so good

Secret

23:43

0

Q: Is the signal detected by LIGO a result of the merging of the horizons or the singularities?

Regarding gravity waves, some YouTube videos show simulations of the gravity waves detected by LIGO in August of 2017. Is the "chirp" the result of the merger of the event horizon or the merger of the singularities?

general-relativity gravitational-waves ligo

Wonder if it just fuse without a transition

Transcript for