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  2. 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. 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. 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. 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. Then 4 days ago the thread gainsaid this assertion:
  8. 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.
  9. Draw the mesomeric structures. Acetic acid can dissociate to Acetate, what is also in the list.
  10. We need one "20,000 mittens under the sea"
  11. Janus

    Political Humor

    Or how about "Bernie at 20,000 ft" ( This one was suggested by my Wife)
  12. 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.
  13. 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.)
  14. No, and already covered this in this thread about 4 days ago:
  15. Are children the only people who can't be relied on to give informed consent?
  16. Thank you, these answers are useful,. They are however the low hanging fruit, as it mirrors the history of teaching basic math concepts, which I already have access to. I would love some examples of professional math communication between adult peers (assumed similar level of education, but disparate experience). Those are data points which I do not have alternate access to, but which I assumed would be plentiful in this forum. The answers thus far have exposed that the more difficult math concepts to communicate will be those that lack personal usefulness or familiar analogy. Not everything can be made relatable. I am acutely interested in the difficult to communicate concepts, please share those even if you feel they will not generalize. For example, you were just hired as a very junior engineer to work with GPS satellites, but were a bit fuzzy on time dilation, what did a colleague say that helped you "get it". If I were pressed to identify ideal examples, I would choose the letters between Solvay Conference attendees if they had the benefit of all knowledge and tools up to now. Modern scientists are not the ideal choice because I believe we have lost a bit of the art of communication as a society since that epic era. I would very much like to be proven wrong on that point. Consider it a challenge.
  17. 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 ?
  18. Why does CH3CO2H have a greater nucleophilicity than CH3OH?
  19. I think that is a reasonable assumption.
  20. 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.
  21. 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
  22. \[X_{\alpha\beta\gamma\delta}\left(g^{\alpha\mu}g^{\beta\nu}+ g^{\beta\mu}g^{\alpha\nu}\right)=0\] 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.
  23. 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.
  24. No, and there must admittedly be some nuance involved here. Despite my strong pushback against MigL, I acknowledge my previous several posts inaccurately imply a black and white binary state on this issue of violence. Instead, it's a fine line. Apologies in advance for the long post... I'll work to tighten up my thoughts on this as we proceed... Protests against unfairness in the system should be peaceful. Calling attention to asymmetries in policing and imprisonment and economic inequity itself should nearly always be peaceful, and exceptions rare. I don't support destruction of private property or harm to individuals and neighbors. We gain allies in the fight on principle when we express ourselves peacefully and on the merits, and we lose allies when pockets of violence arise and absorb all of the attention. The violent actions of the tiny few outliers wind up overshadowing the actions of the great many. The most important messages of the cause are lost amid the shade cast by the bright light of fires in our streets and violence in our cities. We keep seeing here even at SFN as we spend page upon page upon page talking about the 4 people who set a fire in Portland or Seattle instead of the 4 Million people who did not and who were calling attention to their just cause. Simply: I'm against violence for reasons of principle, morality, AND strategy. When we see violence in things like the George Floyd protests, it tends to be conducted against innocent targets... against private property and personal businesses which have nothing whatsoever to do with the cause or the systemic issues at play. It harms those who are not involved and does nothing to improve the situation. It's not focused in a way that will drive the change we seek. It simply creates easy enemies and caricatures for simplistic attack by "the other side." This is also why we saw so many false flag operations with police and rightwing nationalists pretending to be BLM setting fires and breaking windows... so many ridiculous fear-stoking claims about the millions of antifa... they knew it would deteriorate support for the cause and distract/derail us from the more important conversation. They were right, and that's exactly what happened. Even here... Everyone should welcome protest that drives change and pushes for police accountability, but that protest should NOT involve setting cars on fire in peoples driveways or breaking the windows at the local gas station or Target supercenter. I can empathize with the anger felt by those doing these things, but I don't condone their actions. Both can be true at once, and this is the point I've been trying (and failing) to convey here throughout. Likewise... Protests against government should also be peaceful whenever possible. I don't support storming the halls of our congress with zip ties, tazers, and shouts that we should hang elected officials in the gallows just erected 100 feet away on the capitol lawn. By all means, express your protest peacefully... make the case about election fraud, and do so with evidence. Gain the hearts and minds of those who disagree with you... make your case in court... but don't engage in vigilantism or mob "justice" like a bunch of rabid dogs. You asked me about American Revolution, and I will say peaceful attempts WERE made... for decades. Even the Declaration of Independence itself was peaceful. It was only after the King sent troops in response to it that the peace was broken. One can argue that was a similar insurrection and that we'd not have a country without it. That's fair. There surely are times when violence is in order once all other peaceful options are exhausted. Peaceful options had not, however, been exhausted with BLM. The peaceful approaches were the overwhelmingly majority. The violence was marginal at best and is being exaggerated... That's the point. What constitutes an appropriate response is also contingent on how the government responds to said peaceful protest. If the defenders of an unjust government use violence to suppress peaceful protest or to imprison those with whom they disagree (like the thousands of Navalny supporters Putin just arrested in Russia this weekend, for example), then perhaps violence is needed, but it still IMO must be tied to an underlying cause which is itself just and fair and which cannot be more successfully addressed by other means. When the government seeks to suppress peaceful protestors, that is perhaps when it is time to look to the words of founders like Thomas Paine who said, "when struggling to defend rights against tyranny, it is the violence which is done and threatened to our persons which conscientiously qualifies the use of arms." ... but not before. At the end of the day, what we consider violent and acceptable is subjective. I don't advocate or support it in the vast majority of cases. There will be exceptions, though. For me, BLM was NOT one of those exceptions. I felt peaceful protest was used 99.9% of the time, and that the movement would have been better received and more effective had that 0.01% not occurred. These threads at SFN are evidence enough of this... Look at how people perceive it. Look at how I'm being misinterpreted as supporting violence because I agree with their cause. Look at how far away we all are from discussing the actual issues which needs to be addressed. For these and other reasons, I don't support violence, even though across the vast chapters in the book of history I'm sure we can find a handful of exceptions that we agree seem to warrant it. tl;dr: Civic resistance is sometimes justified, and that those who oppose injustice and tyranny are sometimes permitted violence in self-defense. To be clear, this isn’t the same as suggesting that protesters ought to resort to arms. Nor do I, and I appreciate you calling me out on it.
  25. 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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