# All Activity

1. Past hour
2. ## Our perspective of the Sun

I agree, and even if I answered it perfectly it would be unlikely to convince them. However it has intrigued me because its a good question really, nothing wrong with that. Well I say question, it was more of an assertion (as always 😄)
3. ## Our perspective of the Sun

Not worth it. You're trying to use reason on a person who thinks NASA (and ESA and Roscosmos and JAXA and CSNA and ISRO) are hiding the truth about the universe. Their confirmation bias would only be triggered by any scientific explanation. There's SO much fundamental misunderstanding going on with a flat Earther it would take complete reeducation to get through. Anyone who believes the Earth is flat doesn't understand gravity, or how stars and planets form.
4. ## Our perspective of the Sun

Hi, I am new to this so please bare with me. I am currently debating a flat earther, and I am unsure how to answer this question accurately. The claim is that the sun cannot be 93,000,000 miles away, as when you view it from a high altitude, the suns arc changes too much. The conclusion is that this must mean the sun is much closer, otherwise its arc wouldnt appear to change to us. I put this down to perspective and explained that if it were 93 million light years away our position would effect our perspective. (I might be wrong there) But I would also like to know if or why this is the case, I havent observed this or been able to. Thanks if anyone can help?
5. Today
6. ## Political Humor

It's remarkable. We quite often get memes about Republicans doing really stupid things. When an elderly man who is a Democrat does something eminently sensible- wearing gloves in cold weather- the internet explodes.
7. ## Do psychopaths need to be cured?

Then 4 days ago the thread gainsaid this assertion:
8. ## O the Riemann Curvature Tensor

Since that is merely a disguised form of your (4), all you are saying is that a tensor that is antisymmetric is antisymmetric. Taking six equations to get to a tautology seems excessive, but isn't wrong. (7) still does not follow from (6). I already gave an example of a non-zero Riemann tensor that satisfies (6). All you've done is shown that a zero tensor is not inconsistent with some of the properties of the Riemann. I have no idea which comment you are referring to.

10. ## Nucleophilicity

Draw the mesomeric structures. Acetic acid can dissociate to Acetate, what is also in the list.
11. ## Political Humor

We need one "20,000 mittens under the sea"
12. ## Political Humor

Or how about "Bernie at 20,000 ft" ( This one was suggested by my Wife)
13. ## Rheostat vs Bridge Rectifier

I was also wondering if he meant a Wheatstone bridge, which uses a similar arrangement with resistors. And yes, rheostats are old-school, and energy wasters ( they also don't play well with compact florescent lights, which is why if you had an home with the old rheostat type light-dimmer switches, you wouldn't want to use CFLs with them). Some of the newer dimmer circuits use SCRs ( Silicon Controlled Rectifiers) circuits, which use duty cycle to control power to the load. And solid state power supplies often replace the old step-down transformer, bridge-rectifier, filter, voltage regulator power supplies.

15. ## A Simple Arithmetic Teaser !

I was curious about how many answers there might be, so I wrote code. I gave up before trying to deal with parentheses, but got the following: (11 - 17) * 13 + 2 + 19 + 101 = 44 (11 - 13) * 19 - 17 - 2 + 101 = 44 (13 + 101) / 2 - 11 - 19 + 17 = 44 (11 - 13 - 17) * 2 - 19 + 101 = 44 (13 - 17 - 19) * 2 - 11 + 101 = 44 (17 - 19 - 2) * 11 - 13 + 101 = 44 (17 - 19) * 11 * 2 - 13 + 101 = 44 (13 - 11 + 19 + 101) / 2 - 17 = 44 (11 - 17 + 19 + 101) / 2 - 13 = 44 (my answer) ((17 - 19 + 101) / 11 + 13) * 2 = 44 ((13 * 17 - 19) / 101 + 2) * 11 = 44 ((19 - 11) * 17 - 13 - 101) * 2 = 44 (13 * 17 - 19) / 101 * 2 * 11 = 44 (Commander's answer, ignoring order) Sensei's answer isn't here because it's not left-to-right order of operations. I wouldn't doubt this is a small fraction of the possible answers, but neither would I bet that it is. (I also manually culled duplicates so I may have removed too many.)

17. ## Do psychopaths need to be cured?

Are children the only people who can't be relied on to give informed consent?

19. ## Rheostat vs Bridge Rectifier

Generally an excellent explanation, +1, but your examples need updating somewhat. Both these examples were used in 1930's electrical equipment but have long since been abandoned as wasteful of power and potentially dangerous as they result in the excessive generation of heat. https://electronics.stackexchange.com/questions/252352/setting-heat-on-electric-stove Electronerd, are you sure you meant a bridge rectifier ? There are many sorts of bridges, but a simple bridge rectifier is not directly comparable to a rheostat. A bridge is a particular sort of circuit configuration containing four circuit components arranged in a 'diamond pattern. Some bridges are used for power control. This application would be comparable to using a rheostat for this purpose, but much more efficient. Such a bridge would be called a 'controlled bridge rectifier' and contain at least one, probably two or four silicon controlled rectifiers (SCR) or TRIACs If you have been reading about bridges for power control are you sure you don't mean this sort of bridge rectifier ?
20. ## Nucleophilicity

Why does CH3CO2H have a greater nucleophilicity than CH3OH?
21. ## Confessions of a Qanon Believer

I think that is a reasonable assumption.
22. ## Rheostat vs Bridge Rectifier

A rheostat is a variable resistor. It controls how much current is delivered to a load. The adjustment is made by moving a slider along to change resistance. A simple example is like this: Light dimmers are an example, as is the heat adjustment knob for an electric range top burner. A bridge rectifier uses diodes, which are arranged in in a manner to convert alternating current (current that alternates its direction flow rapidly) to direct current ( current the flows only in one direction. A diagram would look like this: D1-D4 are diodes. They act like one-way valves for electricity, letting it flow one way through them and stopping it from flowing the other. The arrangement of the diodes is such that no matter what direction the current in flowing from the source, it only flows one direction through RL. If the source current is in one direction it passes from point A through D1 to point D then to the left through RL to point C, through D3 to point B, and then back to the source When the source current reverses direction, it flows from point B through D4 to point D, then to the left through RL to point C, Then through D2 point A before returning to the source. So, no matter what the direction the current flows from the source it flows through RL from right to left. If it helps, think of the wires as streets and the ones with diodes are one-way streets, It doesn't matter whether a car enters through A or B, it has to travel from right to left through RL. Thus rheostats control the amount of current, and bridge rectifiers control the direction of current.
23. ## Do psychopaths need to be cured?

Depends on how we choose to interpret ability to offer informed consent. As a general rule, we assume the child is not capable of consenting in an informed way
24. ## O the Riemann Curvature Tensor

$X_{\alpha\beta\gamma\delta}\left(g^{\alpha\mu}g^{\beta\nu}+ g^{\beta\mu}g^{\alpha\nu}\right)=0$ The coefficient matrix is independent of gamma and delta. For the same alpha and beta various gamma and delta should produce the same value for the corresponding component ,that is, X_{alpha beta gamma delta}=X_{alpha beta gamma’ delta’} If the coefficient matrix is non zero(or zero) for some (gamma,delta ) pair it should remain non zero (or zero) for other (gamma, delta) pairs.
25. ## BLM, Capitol Riot, Hypocrisy and False equivalency -Split from: Blow to US Democracy

I would like to know where I made that comment. I see where I asked a question, and where you replied, and where I mentioned that your meaning hadn't been clear.

27. ## System of equations and one parameter

Dear Joigus, finally I have been working again on this topic after several weeks. While I confirm that with a system of 2 non linear equations and one parameter K, adding the condition of $\boldsymbol{\nabla}J = 0$ works to find the maximum K for which the system has solution, when I try to apply it to a system of 3 equations, this method doesn't work. I do an example to work on it: $\begin{cases} 4x^3 - y + 4xy^2k = 0 \\ 4x^2y + 4y^3 - x - k = 0 \\ 2z + p = 0 \end{cases}$ First of all I have trying to iterate k and I found that the system has solution until $k<=6.9$ resulting $x=0.0302, y=1.2008, z=-3.45$. Then I have calculated the Jacobian of this system: $J = \begin{bmatrix} 12x^2+4y^2k & -1+8xyk & 0\\ 8xy-1& 4x^2+12y^2 & 0 \\ 0 & 0 & 2 \end{bmatrix}$ Calculating the determinant of this I get $\boldsymbol{\nabla}J = 2(12x^2+4y^2k)(4x^2+12y^2)-2(-1+8xyk)(8xy-1)$ But if I add this equation to the above system, imposing it equal to zero, the system has not solutions. In fact substituting $x=0.0302, y=1.2008, z=-3.45$ in the above equation, value is far from zero. Any idea?
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