Re: Echo A2 Methode De Francais
Toni Jarels
Let's say that there is a girl named Sally Function. You want to know if she likes you or not. So since you're in grade school you decide to pass Sally a note (call the function with parameters) asking her if she likes you or not. Now what you plan on doing is asking her this and then telling everyone what she tells you. Instead, you ask her and then she tells everyone. This is equivalent to returning (you getting the information and doing something with it) vs her echoing (telling everyone without you having any control).
In your case what is happening is that when Sally echos she is taking the control from you and saying "I'm going to tell people this right now" instead of you being able to take her response and do what you wanted to do with it. The end result is, however, that you were telling people at the same time since you were echoing what she had already echoed but didn't return (she cut you off in the middle of you telling your class if she liked you or not)
The reason is that "Goodbye" is echo'ed (written) as output, as soon as the function is called. "Hello", on the other hand, is returned to the $hello variable. the $goodbye is actually empty, since the goodbye function does not return anything.
echo renders the text etc into the document, return returns data from a function/method etc to whatever called it. If you echo a return, it'll render it (Assuming it's text/number etc - not an object etc).
and yes, both of them will give us 151 as an output value.
But, in the return case, we will print firstFunction($value) as an int data type.
Otherhand, in the echo case, we will print secondFunction($value) as a NULL data type.
You can try printing each one with var_dump() function to understand what I meant.
One thing that I learned while doing changes in Buddypress is that it uses the return mainly on nested core functions and then with the use of sprintf it binds dynamic variables into the HTML and return that chunck of html back to the main function where it was called and only then it echo out once at the main function. By doing so the code becomes modular and easier to debug.
In magnetic resonance, a spin echo or Hahn echo is the refocusing of spin magnetisation by a pulse of resonant electromagnetic radiation.[1] Modern nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) make use of this effect.
Echoes were first detected in nuclear magnetic resonance by Erwin Hahn in 1950,[5] and spin echoes are sometimes referred to as Hahn echoes. In nuclear magnetic resonance and magnetic resonance imaging, radiofrequency radiation is most commonly used.
In 1972 F. Mezei introduced spin-echo neutron scattering, a technique that can be used to study magnons and phonons in single crystals.[6] The technique is now applied in research facilities using triple axis spectrometers.
In 2020 two teams demonstrated [7][8] that when strongly coupling an ensemble of spins to a resonator, the Hahn pulse sequence does not just lead to a single echo, but rather to a whole train of periodic echoes. In this process the first Hahn echo acts back on the spins as a refocusing pulse, leading to self-stimulated secondary echoes.
The spin-echo effect was discovered by Erwin Hahn when he applied two successive 90 pulses separated by short time period, but detected a signal, the echo, when no pulse was applied. This phenomenon of spin echo was explained by Erwin Hahn in his 1950 paper,[5] and further developed by Carr and Purcell who pointed out the advantages of using a 180 refocusing pulse for the second pulse.[9] The pulse sequence may be better understood by breaking it down into the following steps:
Several simplifications are used in this sequence: no decoherence is included and each spin experiences perfect pulses during which the environment provides no spreading. Six spins are shown above and these are not given the chance to dephase significantly. The spin-echo technique is more useful when the spins have dephased more significantly such as in the animation below:
Hahn's 1950 paper[5] showed that another method for generating spin echoes is to apply three successive 90 pulses. After the first 90 pulse, the magnetization vector spreads out as described above, forming what can be thought of as a "pancake" in the x-y plane. The spreading continues for a time τ \displaystyle \tau , and then a second 90 pulse is applied such that the "pancake" is now in the x-z plane. After a further time T \displaystyle T a third pulse is applied and a stimulated echo is observed after waiting for a time τ \displaystyle \tau after the last pulse.
Hahn echos have also been observed at optical frequencies.[4] For this, resonant light is applied to a material with an inhomogeneously broadened absorption resonance. Instead of using two spin states in a magnetic field, photon echoes use two energy levels that are present in the material even in zero magnetic field.
Fast spin echo (RARE, FAISE or FSE[10][11][12]), also called turbo spin echo (TSE) is an MRI sequence that results in fast scan times. In this sequence, several 180 refocusing radio-frequency pulses are delivered during each echo time (TR) interval, and the phase-encoding gradient is briefly switched on between echoes.[13]The FSE/TSE pulse sequence superficially resembles a conventional spin-echo (CSE) sequence in that it uses a series of 180º-refocusing pulses after a single 90º-pulse to generate a train of echoes. The FSE/TSE technique, however, changes the phase-encoding gradient for each of these echoes (a conventional multi-echo sequence collects all echoes in a train with the same phase encoding). As a result of changing the phase-encoding gradient between echoes, multiple lines of k-space (i.e., phase-encoding steps) can be acquired within a given repetition time (TR). As multiple phase-encoding lines are acquired during each TR interval, FSE/TSE techniques may significantly reduce imaging time.[14]
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