Recent content by Clear Mind

  1. Clear Mind

    Stargazing Does a Radio Telescope Have Aberration and How Does it Affect Its Performance?

    Thanks for the reply! So, summarizing up... if a radio telescope is capable to build directly an image (didn't know they can do it, i mean, not in a directly way), they may suffer of aberration (indeed I've found someone speaking about spherical aberration in the Arecibo radio telescope). But in...
  2. Clear Mind

    Stargazing Does a Radio Telescope Have Aberration and How Does it Affect Its Performance?

    I was studyng my exam of astrophysics laboratory, while treathing the optical aberration I've wondered: does radio telescope have aberration? Is a paraboloid antenna in a single dish affected by coma? and the radio telescope made by arrays of resonant structures? Maybe those are silly...
  3. Clear Mind

    I Cosets: Is [gH] a Subgroup of G?

    I've tryed to prove it, but i didn't succeed. By the way i think I've found a more directly way to show that ##H=[g_1 H]## if ## g_1 \in H##, but I'm stuck: Let's (## \forall g_1 , g_2 \in H##) build two left cosets, ##[g_1 H]## and ##[g_2 H]##, now, suppose that ##\exists \tilde{g}## so that...
  4. Clear Mind

    I Cosets: Is [gH] a Subgroup of G?

    Well, if ##g_1 \in H## than i suppose that ##\forall g_1## and ##\forall h \in H , g_1*h \in H## so my left coset ##[g_1 H]## it's a subgroup. Mumble ... i think that if ##g_1 \not\in H## than ##\forall h \in H##, ##\tilde{g_1}=g_1 * h \not\in [g_1 H]## (but ##\tilde{g_1} \in G##); so if you...
  5. Clear Mind

    I Cosets: Is [gH] a Subgroup of G?

    Hi, this week I've started to study group theory and there's a thing that i don't understand about cosets: Suppose to have a group ##\textit{G}## and a subgroup ##\textit{H}##, than ##\forall g \in \textit{G}## i can build my left coset ##[g \textit{H}]##. Now, here's my question: Once you have...
  6. Clear Mind

    Question about conditions for Force Free Fields in plasma

    My question is about Force Free fields in the study of plasma stability (in MHD regime): Consider an isolated ideal plasma in an equilibrium state (where the effect of selfgravity is negligible), from the Navier-Stokes equation we get that: $$\vec{\nabla} P = \frac{1}{c} \vec{J} \times...
  7. Clear Mind

    Effects of emitter capacitor in the BJT CE amplifiers

    Thanks for the answers guys, you all make my day! I saw that you were discussing about internal resistance of the base. You can easily calculate the base resistance using the ##\pi##-hybrid or the ##T## model of BJT, they are both correct and their usance depends on the situation. For instance...
  8. Clear Mind

    Effects of emitter capacitor in the BJT CE amplifiers

    So we can affirm that (for small signal model) when ##C_E## is present the amplifier behave like a common emitter amplifier without ##R_e##. While if we remove ##C_E##, the amplifier behave like a common emitter with a emitter resistance ##R_e##?
  9. Clear Mind

    Effects of emitter capacitor in the BJT CE amplifiers

    Suppose to have a BJT Common Emitter amplifier like the one below: Now, if we send a signal ##V_{in}## with a frequency belonging to the midband frequency interval, we can consider ##C_1, C_2,## and ##C_E## as short circuit. Questions are: 1) What is the effect of ##C_E## (excluding its role...
  10. Clear Mind

    Question about input/output resistance

    Thank you very much for the help guys
  11. Clear Mind

    Question about input/output resistance

    The question it's easy. Suppose to have a black box circuit, it will have an input resistance ##R_{in}## and an output resistance ##R_{out}##, all the books and texts argue that it's good to have a big ##R_{in}## and a low ##R_{out}##, but why?
  12. Clear Mind

    What is the Nuclear Spin of Fluorine-19 and How is it Calculated?

    My apologies but I'm not understanfding what you mean, for example take the ##^{43}_{21}Sc_{22}##. It have 22 neutron (so we don't need to care about), and 21 proton which are filled until ##1f_{7 \backslash 2}##. There's only one proton unpaired so nuclear spin ##I## should be ##\frac{1}{2}##...
  13. Clear Mind

    What is the Nuclear Spin of Fluorine-19 and How is it Calculated?

    I was trying to calculate the ##^{19}_{9}F_{10}## nuclear spin using the nuclear shell method. From what i know the nuclear spin for a nucleous with odd ##A## is the total angular momentum ##J## of the stand-alone nucleon: P: ##(1d_{5 \backslash 2})^1## (stand-alone nucleon) N: ##(1d_{5...
  14. Clear Mind

    What Is a Pomeron? | Particle Properties Explained

    As the title says, what is a pomeron? I thought it was a particle but i can't find anything on the PDG ... If is a particle what are its properties?
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