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Posts posted by Sensei

  1. 1 hour ago, Cynic said:

    I particularly like the one about cheese consumption and dying by becoming entangled in bedsheets.

    One dishonest person can get two functions or datasets from connected or completely different disconnected areas of science, or non-science crap, and the only common thing will be their mathematical similarity of curvature. There is infinite such mathematical equations which look very the same. Especially if dishonest person will lay them down on the same graph, offset little, eventually scale etc. etc. The same do astrologists, soothsayers etc.

  2. He has to make computer application, which can learn (i.e. put records to database) phrases, and then retrieving them on demand from database. That is how I understand sentence "Design and development* of an expert system that teaches figure of speech"..

    *) shouldn't be here "develop"?

    "Teaching" might be in form of quiz. i.e. application is showing randomly picked up from database phrase, gives couple wrong answers and one correct, and asks user to select one of options. If correct answer is picked, score is increased, if wrong answer is picked, the correct one is highlighted (so user will learn which is correct for future). Scores are put to high-score table to see improvements over time.


    If I am right about your assignment, then such app could have following options:

    1) add new entry to database

    2) remove existing entry from database

    3) edit existing entry in database

    4) retrieve entry from database (a) randomly b) by entering keyword)

    5) quiz for user to check knowledge

    6) show high-scores

  3. 22 hours ago, Strange said:

    In computing, recursion is, in principle, unlimited. But you eventually run out of resources (typically, memory).

    Recursion might end up with overflow of CPU stack, if it is not properly coded (starting from depth limit, dynamically checking available left stack space etc.).

    Reminding you, default Windows OS thread has 1 MB CPU stack size. It is easy to cause overflow. The more arguments passed on stack to function, the more local variables, the quicker it will happen.

    Recursion is typically replaced by software stack to not have to call the same function in the loop.

    1 hour ago, Strange said:

    Not in my experience. Have you ever written a parser?

    At the moment, I am making my own PDF parser. Whether parsing requires recursion strongly depends on what kind of data are being parsed. e.g. mathematical equation can use nested parenthesis, so recursion might be used to handle them.

    Ray-tracing is better example of algorithm that relies on recursion. I even know some 3D applications which were crashing due to overflow of stack when too many reflective and/or refractive objects have been put in the scene and fired rays back and forth between surfaces. Therefor need for option "Ray Recursion Limit" in such engines.

    25 minutes ago, waive15 said:

    I am rolling up my sleeves.

    Start from Wikipedia article about recursion:



  4. On 11/22/2019 at 11:02 PM, Ken Fabian said:

    Mars, like all space locations, presents serious difficulties for mining and refining. I suspect nuclear power would be a minimum requirement for a Mars colony but I don't see how any colony could build and fuel one from local materials without an industrial economic base that is more comprehensive and advanced than an advanced industrial nation on Earth.

    Solar furnace just needs enough area of mirrors reflecting light toward focal point.


    "The temperature at the focal point may reach 3,500 °C (6,330 °F), and this heat can be used to generate electricity, melt steel, make hydrogen fuel or nanomaterials. "


  5. 1 hour ago, Bufofrog said:

    The energy I am receiving from you is sort of a jerk energy.

    What are coefficients to convert this new unknown "jerk energy" to potential energy or kinetic energy.. ? :)


  6. 2 hours ago, Joseph Lazar said:

    Annihilation is probably the most extreme event observable matter can endure.

    ...annihilation of electrons and positrons happen all day long inside of the Sun... and it is nothing unusual.. new positrons are created during fusion of two Hydrogen-1 atoms.


  7. Do you pay special attention to units (dimensions) used in your equations? i.e. units on the left side of equation must match the right side of equation.. It's called dimensional analysis.

    Take for example your the first equation. What is unit of dg and g? Is not the same units/dimensions? (r is in meters, and c is in m/s, obviously) If yes, then how come you have dg/dr on the left and g/c2 on the far right?

  8. 13 hours ago, Mordred said:

    For example if you pass the photon beam through a polarizer lens you can split the original photon wavelength into two seperate beams.

    The two waveforms will be half the wavelength of the original beam.

    Half the wavelength? This would double the energy and frequency... It is not the case..

    Polarization filter passes one (i.e. it is transparent to) photon with "appropriate" polarization, and reflects another photon with "inappropriate" polarization. What is "appropriate"/"inappropriate" depends on angle of polarization filter.

    Energy is conserved prior and after the event. If the original light beam was not polarized at all, half of all photons pass through and other half of the photons are reflected. Wavelength/frequency/energy of the photon is unchanged (or not significantly changed to be detectable by human).

    The simplest example is to place a polarizing filter on the front of an LCD/LED computer screen, and rotate, as shown in this thread:



  9. 18 minutes ago, swansont said:

    That's experimental confirmation, rather than a derivation. The OP's previous post suggests that a derivation is being sought.

    In the first post I read:

    On 11/18/2019 at 11:33 AM, Tor Fredrik said:

    I don't want a derivation


  10. On 11/18/2019 at 11:33 AM, Tor Fredrik said:

    However for some time ago I found a site that described that a scientist did prove E=mc^2 from an energetic perspective by adding together all energy available from different energy types.

    Prior annihilation of electron with positron energy of both particles is:

    E= 2 mec2

    After annihilation there are two gamma photons with energies:

    E = 2 h fc


    2 mec2 = 2 h fc

    Reverse process is called pair-production.


    Compton scattering relies heavily on it as well.



  11. 41 minutes ago, mistermack said:

    Not necessarily. Nitrogen can be a liquid, and so can Copper. It depends on temperature and pressure. So what you are really asking, is why they have different boiling and melting points. 

    Can't help you on that. Something to do with the intermolecular forces. 

    Water is good example of intermolecular forces. Is has mass just ~18.016 u, when air gases Oxygen has mass ~ 32 u (~80% more), and Nitrogen has mass ~28 u (~50% more). Why isn't water gas like Oxygen and Nitrogen? Because it is polar molecule i.e. it has not uniformly placed electrons, and one water molecule bonds with other water molecules around it (forming weak Hydrogen-bonds).


    Yet another related subject is hydrophilic and hydrophobic properties of molecules.



    (typically polar and nonpolar molecules)

  12. 10 hours ago, mistermack said:

    One thing I dreamed up, a few years ago, was a possible way to green some of the world's deserts. I don't know if it would work, it would take some serious political will to embark on. 

    The idea is that you start with a desert or semi desert close to the coast. It has to have a history of regular onshore winds. What you do is to install some serious seawater pumps, a few hundred metres from the shore. When there is any significant onshore wind, you pump seawater upwards, in an extremely fine spray, so that the water evaporates, and the salt falls back into the ocean.

    The humid air travels inland, where it is forced upwards, forming clouds and giving rain. The combination of clouds and rain transform the barren land into rich agricultural land, taxes on which pays for the pumping operation. In time you might even get rivers to flow, enabling secondary irrigation using the same water. 

    If the economics don't add up now, they might in the future, if there is cheap electricity from fusion reactors. 

    Somewhere like the Nullarbor Plain in Australia could be transformed into a real bread basket, with regular rainfall. And all you need is an onshore wind, and the money to operate the pumps.

    The problem with desert is that it has no significant amount of soil which is basically centuries and millennia of dead plants (natural compost). New plants to grow need nutrients. Where are these nutrients? In soil. Gathered from rain, and produced by other living organisms like bacteria and fungi. Water from rain quickly passes through sand, but it last longer in soil. During stormy weather there are thunders. They make NOx compounds, which fall with rain to soil. Plants need Nitrogen to grow. Without Nitrogen they won't be able to grow. It's often the case in plants growing in human apartment. They don't have access to rain, so after months and years soil is exhausted from Nitrogen compounds. I am catching rain on balcony and giving it to my plants. Alternative is to use artificial fertilizers.

  13. On 11/21/2019 at 10:56 AM, Arnold Ungab said:

    lol, a great joke for a non believer but if i ever get tested i will invite you for sure....

    1) did you get my message,


    2) did not you get my message..


    If yes, then be so kind and tell content of my message to you..

    Thanks in advance!


  14. If we have 26 characters in alphabet (a-z) and no other characters, we could pack word to single number, using formula:

    [math]\sum\limits_{n=0}^{n<m} x_n*26^n[/math]

    Character a = 0, .... , z = 25

    Word consisting of { x0, x1, ..... xn-1 }

    Quantity of characters-letters is 26, therefor powering e.g. 26^1 gives completely unused area than previous 26^0, etc. where we can store the next letter of word, etc. with other powers (positive integer n>=0)

    ASCII (8 bits per char) text is equivalent to:

    [math]\sum\limits_{n=0}^{n<m} x_n*256^n[/math]

    Unicode (16 bits per char) text is equivalent to:

    [math]\sum\limits_{n=0}^{n<m} x_n*65536^n[/math]


    Extraction of characters from such packed number can be done using pseudo-code:

    Number x; // initialize it
    while( x > 0 ) {
       int chr = x % 26;
       printf( "%c", chr + 'a' );
       x /= 26;



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