# All Activity

1. Past hour
2. ## Help

Sika publish pretty comprehensive documents safety (15 pages) https://gbr.sika.com/dms/getdocument.get/5fad402e-5b88-3470-a2eb-87bf1b31ef0e/Sikaflex221.pdf The section on personal protection is interesting. Have you read it? and use (12 pages) https://usa.sika.com/dms/getdocument.get/2bc4a3da-b682-3ff9-bbe0-e5b73f217550/General Guidelines_Bonding and Sealing with Sikaflex_v5-2018_EN_US.pdf
3. Today
4. ## Book by Stephen Hawking

I like his book very much
5. ## Can baryon number be violated e.g. in baryogenesis, Hawking radiation ... neutron star?

For a few decades they have unsuccessfully searched for proton decay in room temperature water, what seems interpreted as disproof of this possibility ... but is it really? The same way we could "disprove" nuclear fusion as it practically doesn't happen in room temperature water ... but happens in extreme conditions. So maybe it didn't disprove baryon number violation, only it needs extreme conditions e.g. to get into some higher energy state before decay? Baryon number violation is hypothesized in baryogenesis, Hawking radiation - which need quite extreme conditions. It is required in many models like supersymmetric, or now popular sphaleron. How can we verify this possibility? Talking with particle physicists, they say we just cannot know if it happens e.g. in LHC, checking baryon number is practically impossible there (?) So maybe astrophysical objects to understand orders of magnitude higher energies than we can explain in standard way? For example https://www.space.com/35846-brightest-farthest-neutron-star-discovered.html
6. ## Help

The two that caught my eye are the ethylbenzene and isocyanate. Ethylbenzene has relatively low toxicity, but its chronic ( long term effects ) might lead to cancer. The isocyanate may be related to MDI ( MethyleneDiphenyl diIsocyanate ), which is not very volatile, but is a sensitizer, and once sensitized, even small exposures can lead to systemic reactions such as those listed in the MSDS. The MSDS also lists appropriate PPE to wear for your protection.
7. ## Help

Ok so this might sound really dumb. But I was wondering if anyone can help me out here. I got this caulk sealant on the pavement and I was trying to remove it. I used some gasoline to try to remove it. It worked but it got me thinking about my long term heal. I have some pictures of the sds below, this stuff seems pretty bad to inhale, but my main question would be, by adding the gasoline would this cause it to become more toxic? I was outside when doing this.
8. ## Air pressure at Earth's center

The ideal gas law describes the behavior of a particular parcel of gas without any gas entering or leaving, so N would be constant in the equation. After the substitutions, the only things removed from the integral are $\mu, m_H$, and $K_B$, which are constants. Edit: I take that back. In the laboratory, one would normally be dealing with a fixed quantity of gas in a container, but you could also have an imaginary boundary within a volume of air through which gas could pass, so N could be variable. However, N is not in the integral and it's still true that $\mu, m_H$, and $K_B$ are constants, so removing them from the integral is valid. Further edit: The variability of N is implicit in the variability of P, rho, and T. Once the physical substitutions have been made, any constants in the integrand can be removed from the integral.
9. ## 2 fun ideas

Some studies on low gravity pregnancies, suggest the children might develop abnormally and find dealing with higher levels of gravity borderline impossible, while others suggest the embryo might fail to develop at all. So I'd say your fist idea is pretty plausible, may need to be larger though to avoid nausea. As to the second, you are talking about a Utopia. Be nice, but we have a long ways yet to go as a society. On the whole things are gradually improving though.
10. Yesterday

12. ## The Omniscience Principle

https://www.phil.uu.nl/~iemhoff/Mijn/Slides/seattle17.pdf intuitional logic
13. ## Lorentz-contraction

(I mean, your relative speed is not cero, but it is as if you were stopped, as it remains running away from you at c)
14. ## What is time? (Again)

My apologies again. I made a mistake here (as usual): $\int_{S}\textrm{curl}\boldsymbol{v}\cdot d\boldsymbol{S}=\oint_{\partial S}\boldsymbol{v}\cdot d\boldsymbol{l}$ The circuit must be the boundary of the surface. I didn't mention it, but it was always on my mind.
15. ## What is time? (Again)

Good stuff, +1. However you missed the zero dimension. In one dimension the 1 dimensional differentiable manifold is the interval [a , b] , a function of one variable f(x) and the boundary comprises the two points a and b. so the theorem says that $\int\limits_a^b {df = f(b) - f(a)}$ IOW the Riemann integral. The link to time (I am trying to avoid the word connection) is that in space-time, time is somehow one of the variables in the manifold.
16. ## Air pressure at Earth's center

Surely N is not " the number of molecules",, but " the number of molecules between r and (r+dr) ? In other words surely N is a function of r and increases as the gas layers become more dense ? Haven't you treated N as a constant in your integration? I look forward with interest to your integration of g/T, both of which are also functions of r. I looked at this analysis which is a standard fluid mechanics/meteorology solution. I did not pursue it because there are direct measurements that support the assumptions it makes and provide many calibration points for the constants. As a matter of interest, this article is a bit old but contains estimates of the variation of gravity, temperature and pressure in the rocks as functions of depth. https://www.researchgate.net/figure/The-pressure-at-different-depths-in-the-Earths-interior_fig12_228377528 Look at pages 12 through 17 in particular
17. ## Lorentz-contraction

I can see that, but I am not in position to understand them properly This said, thanks, Markus: Even without tensors, I get your point about the acceleration not being equal to curvature. I've got that wrong As I see it, if the particle, galaxy on the boder, or whatever object is in the direction of your movement, is running away from you at c, there is no problem As you are not travelling at c, the object will keep travelling away from you at c (this speed being absolute) No way to contract the space between you and it because your speed relative to it is cero...

19. ## Is there such a Thing as Good Philosophy vs Bad Philosophy?

Not entirely true. But so what? I have no idea what that is supposed to mean. When science produces a result it is equally valid whatever your personal ideas are. We all benefit from scientific progress (unless you reject it). Nice straw man. No one said that. But the fact that equality can be proved, means that we can have a certain level of confidence in the consistency of models. It is then a matter of comparing that model (the map) to observations (the terrain) and refining it as necessary. When it comes to science, for example gravity or evolution, we do not each have a unique model. If you are talking about views outside of science, then, well... duh and thank you, Captain Obvious. One of the roles of philosophy is to explore what the roots of belief and knowledge are. (As someone who knew anything at all about philosophy would know.) So hardly irrelevant. (And I think most people with some understanding of philosophy or science would say that knowledge can never be complete.) Many people have attempted, with varying degrees of success, to put philosophy on a formal basis starting from fixed definitions. Some very interesting results have come from such work. Christ. Give us some warning when you are about to throw in a non-sequitur like that. I think the sudden change of direction has given me whiplash. Please provide some evidence that "most people" believe this. So you don't believe in "laws" but you do believe in "logic" underlying reality. Would that be the "laws of logic", by any chance.
20. ## How do I dissolve 5% caffeine to make a serum?

Strong solutions of urea, glycerine, and/ or propylene glycol might be better solvents than water. It's possible that the caffeine is in suspension rather than solution. Why would you bother?
21. ## Air pressure at Earth's center

It seems a number of people are converging on the Newtonian hydrostatic equilibrium equation. dP = - g(r) p(r) dr where P=pressure p=radius dependent density and g=radius dependent gravity https://en.wikipedia.org/wiki/Hydrostatic_equilibrium I only gave the Toll/Opp/Volk root because I was intending to use data tables I'd seen for proto-stars before fusion begins. However as Martoonsky pointed out, this will not work because the weight of the gas is affected by the much denser solid portions of the Earth around the bore-hole. Further complicating matters, if we are not going to consider an insulated bore-hole, then p, the density, is dependent on pressure, which is dependent on temperature of the surroundings ( up to 5500 deg as Martoonsky stated ). Back to the drawing board ...
22. ## Is there such a Thing as Good Philosophy vs Bad Philosophy?

I personally don't take offence at the concept of science being wrong, even though I use my leisure time mostly to learn more about it and I've made of it my method to try and understand the world better, like most of us here I would say. I don't think science aims for absolute truth. It's not about being right or wrong beyond any doubt. It's about being more right and certain and less wrong and uncertain, and pushing the limits of doubt and ignorance. Science doesn't provide us with a magic wand to dictate ethics either. It evidences correlations, most of them of statistical nature. It sheds light on plausible causal connections, it refutes previous ill-conceived ideas. If we do that, we are in a better position to take better decisions, diagnose better, tackle evil before it happens. But this can only be achieved by adding to the structure more layers of rational thinking and open discussion. Our understanding is never complete. What kind of philosophy marginalizes individuals? Do you mean something like social Darwinism? It's not a universal trait of philosophy, AFAIK. I'm guessing you've voted that there are good and bad philosophical theories...
23. ## Is there such a Thing as Good Philosophy vs Bad Philosophy?

"History warns us that it is the customary fate of new truths to begin as heresies and to end as superstitions" I am not suggesting that real science is wrong about everything or anything. I am merely saying that science looks at everything from the same perspective which is reductionistic and dependent on definitions and axioms. Since all ideas and all progress are individual it is also dependent on models and language for all practical purposes. Just because 2 + 2 = 2 x 2 does not make our models correct or like one another. Each of us has a unique model and each of us sees the interrelatedness of scientific and mathematical knowledge but this can't make any of us correct about anything either. Philosophy falls by the wayside because everyone's understanding is solid, so who needs mere words to ruin the wonderful symmetry found in nature? Of course the problem is we have no roots in anything except beliefs, language, and ephemeral definitions and meaning of language. We have no roots except our models constructed from our interpretation of the reality disclosed by proper experiment. "Philosophy" becomes irrelevant when our understanding is complete. I am saying that philosophy could contain a broader perspective if it had a vocabulary with fixed definitions but mostly I am saying that any philosophy that marginalizes individuals is evil.
24. ## Thought experiment: how would physics develop without Einstein?

General relativity has this huge problem of being non-renormalizable ... while it wasn't an issue when it was introduced, a few decades later it would make GR extremely difficult to accept - there would be needed very strong experimental evidence to give up renormalizability - which experiment could it be? GR can be seen as a sequence of corrections in Taylor expansion - without Einstein we might now slowly introduce such succeeding terms ...
25. ## Air pressure at Earth's center

People are going off on a number of tangents here, and that's cool. I like to see the different ideas. This is going to be my first really substantial post. I'm going to define the problem that I will be working on in a bit more detail. If others want to work on different variations, that's fine with me. I didn't intend for it to be an engineering problem. I'm not going to concern myself with how to construct or maintain the borehole. An alien race may have come along and punched a straw through the earth, or Harry Potter may have done it by magic, whatever. Here's the physical setup: there is a straight, narrow, cylindrical hole through the earth, passing through the center and open to the atmosphere on both sides. This will be known as "the borehole". The walls are strong enough to withstand the pressures exerted on it by the earth. In my model, the walls of the borehole will be sufficiently thermally conductive that the air in the borehole will be the same temperature as the earth at that radius. The problem is to determine what the air pressure would be at the center of the earth under these conditions. My original model was starting to get rather complicated, so I decided to start off with a very simple model, find a solution for that, and then perhaps work toward something more complicated. Here are the details of my first model: * The earth is spherical with radius $R = 6.371 * 10^6 m.$ * The earth has a constant density. * The earth's temperature varies linearly from the core to the surface. * The ends of the borehole have a temperature of 288 K and a pressure of one bar. * The temperature at the center is 5500 K. * The ideal gas law applies throughout the borehole. * The air in the borehole is in hydrostatic equilibrium. I will not consider effects due to the rotation of the earth. Distances are measured relative to the center of the earth, i.e. $r = 0$ at the center and $r = R$ at the surface. We want to determine $P_0$ which is the air pressure at the center of the earth. $P_R$ = 1 bar is the air pressure at the surface of the earth. I was originally considering using this equation: $P_0 = P_R + \int_{0}^{R}\rho g dr$ where $\rho$ is the density of the air and $g$ is the acceleration due to gravity. I thought this equation would give the result, but I wasn't sure how to express $\rho$ as a function of $r$, nor how to include the effect of the temperature. With a little help from Astronomy Education at the University of Nebraska-Lincoln (https://astro.unl.edu/naap/scaleheight/sh_bg1.html), I came up with the following: $dP = -\rho g dr$ We can then use the ideal gas law to come up with a substitute for $\rho$: $PV = NK_BT$ where $V$ is the volume, $N$ is the number of gas molecules, $K_B$ is the Bolzmann constant, and $T$ is the temperature in Kelvin. For $N$ we can substitute $\frac{M}{\mu m_H}$ where $M$ is the total mass of the gas molecules, $\mu$ is the average mass of an air molecule in hydrogen atomic mass units, and $m_H$ is the mass of a hydrogen atom. Thus we have $PV = \frac{MK_BT}{\mu m_H}$ and $P = \frac{M}{V}\frac{K_BT}{\mu m_H} = \frac{\rho K_BT}{\mu m_H}$ We can solve for $\rho = \frac{P\mu m_H}{K_BT}$ Substituting this expression for $\rho$ in $dP = -\rho g dr$ we have $dP = -\frac{P\mu m_H g}{K_B T} dr$ and $\frac{dP}{P} = -\frac{\mu m_H g}{K_B T} dr$ Integrating downward from the surface to the earth's center, we have $\int_{P_R}^{P_0}\frac{dP}{P} = \int_{R}^{0}-\frac{\mu m_H g}{K_B T}dr = -\frac{\mu m_H}{K_B}\int_{R}^{0}\frac{g}{T}dr$ $\int_{P_R}^{P_0}\frac{dP}{P} = ln P \vert_{P_R}^{P_0} = ln P_0 - ln P_R = ln \frac{P_0}{P_R}$ Thus $ln \frac{P_0}{P_R} = -\frac{\mu m_H}{K_B}\int_{R}^{0}\frac{g}{T}dr$ and $\frac{P_0}{P_R} = e^-(\frac{\mu m_H}{K_B}\int_{R}^{0}\frac{g}{T}dr)$ and finally, we have an expression for the air pressure at the center of the earth: $P_0 = P_R e^-(\frac{\mu m_H}{K_B}\int_{R}^{0}\frac{g}{T}dr)$ It's getting late, so the completion of the calculation will wait for another day.

Loop through all 4,000 pages of members in the search and scrape their content with Selenium or some such lol? Might want to set a delay though could cause issues with site reliability.
27. ## Implausable hybrids

https://en.wikipedia.org/wiki/Mule https://en.wikipedia.org/wiki/Hinny
28. ## First Year Computer Science Student can't code

Zed Shaws book." Learn Python the Hard Way". Was very helpful to me. I think that writing some sort of text adventure is an excellent way to learn the basics of most any language. That's why I liked that book so much because it taught Python concepts through making the game
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