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Marian Stofka

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Dr.

Marian Stofka is with the Slovak University of Technology, Faculty of Electrical Engineering and Information Technology in Bratislava, Slovak Republic.


Marian Stofka

's contributions
  • 05.06.2014
  • Can you analyze this circuit?
  • Martin, if I were a teacher in the mentioned class, I had no problem to apologize to pupils and correct the drawing as you describe. Another possibility is to replace "10 A" by "20 A"; thus "12 A" notation can remain at R1 = 2 Ohm and Ix = 8 A. A teacher, who is not apt to apologize, could claim, that parallel with a lead from positive pole of battery to upper terminal of R1 there as an another identical lead, which is invisible, transparent (SnO2 or ITO type) or hidden; yet it carries another 10 A current; so the total supply current is 20 A.
  • 03.06.2014
  • Ohms per square
  • "even if the cross section isn't really square," - it should be stressed for young readers, that cross-section is meant here as slicing the resistor, or more precisely its resistive layer, by a plane planparallel to base of the resistor. The real SMD resistors resemble highly the above "perspective view" with the exceptions, that cyan "wires" are omitted and "Depth" within the above formula is the thickness of a resistive layer deposited atop the nonconductive body, usually alumina, of the resistor.
  • 03.05.2014
  • A blimp of LEDs
  • Weigh of the LEDs themselves can be estimated as 235,200x1gram=235.2 kg. Even more interesting is powering of these LEDs. If all LEDs were simultaneously operating @0.1A each (some 15% of LEDs are turned on at above picture), the installed power requirement could be 3Vx23,520A= roughly 70 kW. At left bottom corner of the picture some dark line can be discerned; is it a power cable?
  • 03.04.2014
  • 200 lm/W efficiency barrier smashed
  • I was eager to look at data of the first 200 lm/W LED commercially available. Inside the datasheet a maximum typical efficacy of 131 lm/W can be found for "Lime" LXZ1-PX01 type @ 500 mA. At 350 mA the efficacy can be expected mildly higher, as the efficacy-vs-current is a "little bit" concave curve; but scarcely it reaches 200 W/lm. A possible conclusion: April 1 is approaching fast...
  • 02.20.2014
  • Is Technology More Advanced than it Appears?
  • "What I get from real covert sources I do not talk about on the Internet" Dennis, I am far from scaring you, but now you seem to be really threatened. The only alleviation of your situation could be, if the "sources" were associated/identified with those services, mentioned earlier.
  • 02.05.2014
  • Today single-molecule LED – Tomorrow molecular-scale computing
  • "Today single-molecule LED...": perhaps a more truthful heading could be "Today single-macromolecule LED..." I dare to return to thiophene itself. For those readers, who had not a pleasure to pass through organic chemistry; or passed through, but forgot about thiophene: Thiophene is a heterocyclic organic compound with four atoms of carbon (grey balls in Fig.1 above) and one atom of sulfur (yellow ball in Fig.1) ordered with their bounds as a ring. Two of these bounds between neighboring carbon atoms are unsaturated, or double. Each of the four carbon atoms has a bound with an atom of hydrogen (white ball in Fig.1). At polymerization of thiophene, two hydrogen radicals close to sulfur atom are released and the two open bonds are coupled to two other such "depleted" molecules of thiophene; etc. Thus a string of molecules originates.
  • 01.23.2014
  • Funniest schematic ever
  • Author of the above schematic definitely is not a believer; otherwise he/she couldn't put the "666 timer" atop and the vessel with holy water abottom. Moreover, the holy water should be kept at high potential and not grounded, as above.
  • 01.31.2014
  • E-whiskers could turn robots hairy
  • If mixing of chemical and other notations together will continue, it could lead to a "Babel Tower" of abbreviations. At first glance, "AgNP" used above, looks like some silver(Ag)-nitrido (N)-phosphide(P). What about denoting the "silver nano particles" as shortly as Ag-nplcs ??
  • 01.26.2014
  • International Space Station (ISS) power system
  • There are also further reasons, why not 300 W/m2. The solar panels contain supporting frames and leads, which represent a fraction of the area of panels, but do not generate power. Also the conversion efficiency should be defined clearly, if it is valid for a wavelength, where an Si cell is most sensitive, namely around 1.1 umeter; or if it holds true for a blackbody radiation held at around 6000 Kelvin (modeling of Sun), where a dominating wavelength is around 0.55 umeter. Last, but not least; if the cell would be operated at MPPT (Maximum Power Point Tracking), then 50% of electrical power generated can be acquired at terminals of the cell and the remaining 50% of power heats the cell.
  • 01.15.2014
  • Tips & Trends: Tackle LED compatibility
  • There is a saying attributed to Konfucius, that "It's better to lit even a little candle, than to comply of darkness." The contemporary version could be: "It's better to turn-on a 10W LED lamp..."