Search results

  1. joema

    Unrecoverable read errors and RAID5

    A number of popular-level articles have been published saying that RAID5 is increasingly impractical at larger data volumes due to the chance of an individual HDD having an unrecoverable read error (URE) during the rebuild phase. I think the underlying math which produced this conclusion may be...
  2. joema

    Polar graph for engine balance on common types?

    In a late 1980s trade journal, I saw a full-page of polar balance diagrams for each major engine type. For each engine type (V6, V8, inline 6, inline 4, V12, etc) a circular polar chart was presented with overlaid color-coded graphs showing 1st, 2nd and 3rd order balance for 360 degrees of...
  3. joema

    Formula for compounded contributions

    Homework Statement What is the formula for compounded annual contributions which increase at a fixed % rate, yet where the principal interest rate is 0%. IOW the classic "money under the mattress" savings where the yearly contributed amount increases at a fixed %. E.g, year one contribution...
  4. joema

    Angular acceleration given force, moment arm and inertia?

    Homework Statement Find angular acceleration in deg/sec^2 given the following factors: - Total mass: 4889 kg - Moment of inertia: 4620 kg*m^2 - Moment arm length from center of mass: 1.5 meters - Force on moment arm tangent to mass: 1779 newtons Homework Equations torque = force...
  5. joema

    Origin of phase angle nomenclature?

    It's common to express phase differences between two sinusoidal waveforms as a "phase angle", with a full cycle corresponding to 360 degrees. What is the origin of this nomenclature, and why is phase expressed in degrees? Examined naively, the time domain representation of two waveforms...
  6. joema

    Polar coordinates of complex impedance

    The question is: "In polar coordinates, what is the impedance of a circuit that has an admittance of 7.09 millisiemens at 45 degrees?" The official answer is: "141 ohms at an angle of -45 degrees". I don't understand this. 7.09 millisiemens is 141 ohms, and the positive phase angle...
  7. joema

    Aftermath: Population Zero view of unattended nuke plants

    "Aftermath: Population Zero" view of unattended nuke plants The National Geographic TV special called "Aftermath: Population Zero" explored the consequences if everyone on earth vanished, particularly from the standpoint of suddenly unattended technical and industrial systems, and especially...
  8. joema

    How to calculate achievable flashlight beam divergence

    Assuming a typical white-light focusing flashlight (e.g, Mag-Lite) with a parabolic reflector focused to produce a convergent/divergent beam, how do I calculate the smallest achievable spot size (i.e, smallest beam cross sectional area) at a given distance? How does this vary with reflector...
Top