• Abdelkader Touhami asked a question:
    Anyone works on leakage currents in HEMT ?

    there is someone who works on leakage currents in HEMT. I want to know more about the physics mecanisms in this devices 

  • Ali Asghar Moshtaghie added an answer:
    Can we use heavy metal concentration ref. values like UCC for sediments of all the regions globally?

    During calculation of Heavy metal contamination levels of  a region through its sediments, can we take base line values like UCC for calculation? If it is so, we may have a chance to miss the assessment of real contamination level of a region. How will you clarify this issue?

    Ali Asghar Moshtaghie · Isfahan University of Medical Sciences

    please make your question more clear.The ref concentration are appeared in most clin chem book

  • Derek Abbott added an answer:
    Do the number of electromagnetic modes in a coax cable depend on its length?
    In a recent paper it has been stated: "It is true that TEM wave modes in a [coax] waveguide do not have a low-frequency cut-off versus the diameter of the [coax] waveguide, but this argument is irrelevant because wave modes do have a cut-off versus the length of the cable. This does not imply that the electrical transport itself has a cut-off; it solely means that, when wave modes are forbidden, electrical transport takes place via non-wave phenomena—such as drift and relaxation—which constitute the form of transport in the quasi-static region of electrodynamics."

    See: http://vixra.org/abs/1403.0964

    This seems to run counter to the mainstream view that electromagnetic wave modes exist even when the wavelength is longer than the cable.

    How can any propagation of electromagnetic radiation occur without waves?

    The question is this: what is the simplest, clearest, and most convincing argument that modes exist independently of length of the coax?

    What is the clearest way to explain it to a skeptic? Any ideas?
    Derek Abbott · University of Adelaide

    Ok, we have now written a paper replying to Laszlo's points:
    https://www.researchgate.net/publication/260166605

    In a nutshell, we believe Laszlo has essentially conflated  standing waves with propagating waves.  This is the only way we can see to understand some of his statements.

  • AjayaKumar Kavala added an answer:
    What is the meaning of self consistent? How will it help in poisson, continuity equation?

    See above.

    AjayaKumar Kavala · Indian Institute of Technology Patna

    @Mainak Saka, Thak you

  • Alan Robinson added an answer:
    What is the fundamental difference between modulation instability(MI) and Four Wave Mixing (FWM)?

    The standard text books say that MI and FWM are the different descriptions of the same phenomenon. These say that the MI is the temporal description of the breaking of a CW into pulses. The same thing when viewed in frequency domain manifests itself in the generation of symmetric sidebands around the pump and this is called FWM. But I have doubts regarding that when multiple FWM process is described, why the MI and FWM are treated differently?

    Alan Robinson · 4D Optics

    Kenneth Schepler's reference to Agrawal's book is worth following.

    MI can be explained as a FWM process, but does not require that the input signal is pulsed.  Instability is generally only seen in fibres with anomalous dispersion, where the phase mismatch due to chromatic dispersion is offset by the phase shift induced by self phase modulation (SPM) of the carrier.

    Any amplitude modulation of the signal results in phase modulation via SPM.  Simultaneously, fibre dispersion converts the newly-generated phase modulation to amplitude modulation.  For anomalous dispersion, the converted amplitude modulation reinforces the original perturbation.  The amplitude perturbation is amplified, with peak gain at modulation frequencies such that the rate of generation of phase modulation by SPM and the phase rotation by chromatic dispersion are exactly balanced.  This can be described as phase matched four wave mixing in which the unmodulated optical carrier acts as a degenerate pump, and power is transferred to two equally spaced Stokes and anti-Stokes sidebands.

    For fibres with normal dispersion (negative ps/nm/km), FWM between modulation sidebands and carrier still occurs, but the transfer of energy between carrier and sidebands oscillates along the fibre, with no exponential growth of amplitude modulation.

  • Ankit Verma added an answer:
    What is the relation between FeO and Fe2O3 in steel-making slag?

    Any empirical co-relations or method to link it with any physical measurable quantity will be appreciated.

    Ankit Verma · IIT Kharagpur

    Yes. or some relation using the oxygen potential. The problem is that in literature we have plenty of data using FeO or FeO and FeO1.5 but in industrial data available has Fe total in their analysis. I may looking for something to bridge the gap.

  • Dr. Mrutunjaya Bhuyan added an answer:
    What is the best field to do PhD and where?

    I am currently doing Masters program. And I am looking for PhD program, which branch in physics will be a better choice and for that field which country will be a good choice?

    Dr. Mrutunjaya Bhuyan · Chinese Academy of Sciences

    That depend on ur interest. All the branches of Physics are quite interesting. If there is some application toward the medical science like DNA etc. Then it is very much interesting. You try to get some knowledge of Physics in different branch of physics from the below link: 

    http://physics.about.com/od/physics101thebasics/f/FieldsPhysics.htm

    Hope this quite important for you. 

    Best wishes

  • Cecilia Lewis Kausel added an answer:
    How can we control for other factors in a study of teachers' influence on students' academic performance in physics?

    There are many factors influencing students' academic performance in physics such as students' background, parental influence, poor laboratory equipment etc. Study on teachers' influence on students' academic performance is good, but how do we control for the influence of other factors? Some people argued that some result from the teachers' influence may not be reliable since other factors are simultaneously working on students.

  • Adarsh. M. J. added an answer:
    Does god really exist? Or is it just a product of a weak mind?
    Our universe is entirely self-contained, natural selection is controlling our evolution,so the question is what role is there for "god" to play?
    Adarsh. M. J. · B.V. Bhoomaraddi College of Engineering and Technology (BVBCET)

    People don't believe in GOD because they are good..... they do it thinking... if they believe in GOD.... gods going to make them good.!

  • Doug Dykaar added an answer:
    Is there any Non-linear optical material whose change of refractive index with incident LASER intensity is high?
    For CS2 it is high but we find new material better than it.
    Doug Dykaar · DifTek Lasers, Inc.

    Organics and Lithium Niobate will have low damage thresholds. Also be wary of large refractive index changes that are close absorption edges.

  • Kamlesh N. Pathak asked a question:
    Do we know enough physics for the prediction of the ionosphere behavior?

    Ionosphere

  • Chetan R. Kathad asked a question:
    What is the difference between inertial mass and gravitational mass?

    Inertia and Gravity both are inherent properties of mass, inertia totally depends on the amount of mass contained, but not thorough clear picture about gravity..

  • Yesid Goyes added an answer:
    Is there any model or equation for ridge dynamics?

    I have a 2D system, you can think of it as a 2D sheet. There is a formation of ridges in this sheet when it is given a constant in-plane pressure. I want to model the ridge dynamics. Is there any model, equation or theory for the ridge formation?

    Yesid Goyes · Industrial University of Santander

    Transport away from mid-ocean ridge by plate motion (Davis and Lister, 1974)

    Davis, E.E., and Lister, C.R.B., 1974, Fundamentals of ridge crest topography. Earth and Planetary Science Letters 21(4): 405-13.

  • Arshad Ali Shedayi asked a question:
    Confusion in selecting impact factor journals.

    It is indeed creating lot of confusion among the researchers especially the young ones in selecting impact factor journals. There are journals having different types of impact factors, for example ISI/SCI, SCI expanded, Global impact factor and Universal impact factor. It really creates frustration among the academia. Which impact factor journals are credible and why? Why there is not one type of impact factor? Where the young researchers should go to resolve this issue? All scientists, scholars and researchers are requested to comment and give solid reasons and guidelines please.   

  • Ljubomir Jacić added an answer:
    What is the good practice of self-citation?
    Some questions come to mind, like:
    1. In what part of the new paper shall an author self-cite a previous research of his/her own? the introduction? results? discussion?
    2. In what part of the new paper does self-citation increase the most its significance?
    3. Shall the author's new papers be self-cited or the old ones?
    4. Does self-citation in the discussion support the findings?
    5. Does self-citation increase the impact of the paper? its citation? its merit? the popularity of the author?
    6. Is it preferable that the papers the author has second-authored be self-cited more than the those first-authored?
    7. In what cases might self-citation hurt the chances of the new paper to be published successfully?
    Ljubomir Jacić · Technical College Požarevac

    Dear @Faysal, it is difficult question and it deals with ethics! I have no good answer about good practice of self-citation(s) , but I feel free to recommend some readings on this issue! "From an economics standpoint, self-citation is the easiest method to boost one’s citations. Every author knows this and cites his own articles, however peripheral their relationship is to the topic at hand. Editors know this as well, and some have been caught coercing authors into self-citing the journal"!

  • Mukulika Jana Chatterjee asked a question:
    Tight binding approximation of energy

    Please see the attached file. I have difficulties to solve part c of the problem.I can not find the values of Kx, ky, kz.

    The question is from  the ' Solid State Physics' by Ashcroft & Mermin, chapter no. 10 and question no. 1.

  • Cyril Mechkov added an answer:
    How do we create virtual electrical elements in electronics? Are they really "elements" or circuits?

    To build electronic circuits, first of all we need the natural electrical elements resistors, capacitors and inductors. However, in many cases we are not satisfied with the performance of these passive components and try to improve them in an artificial way. For this purpose, in electronics we have been inventing a variety of clever and sophisticated techniques to create artificial (synthetic, virtual) elements. The question is, "How do we make virtual elements?"

    Like magicians, in electronics we convert the imperfect passive elements into perfect active "elements" (by applying the virtual ground configuration)... or we transform some element (a capacitor) into its dual (an inductor) by swapping the voltage across and the current through it (gyrators)... or we transmute the passive circuits into their opposite mirror doubles (negative impedance)... or we even create completely new electrical elements (memristors)... Thus, for some reasons, we frequently replace the natural electrical elements by their circuit equivalents - a gyrator, multiplier, memristor, negative resistor (capacitor, inductor...)

    It is important to note that all these virtual "elements" (electronic circuits) emulate only particular properties (usually, the time behavior) of the genuine elements... they are not real, they are just an illusion...

    Genuine elements. The general property of passive electrical elements is taking (consuming) energy from the input source; resistors dissipate this energy while capacitors and inductors store (accumulate, "steal") it. But how do they do it?

    Let's assume the considered passive element is connected in series to the exciting voltage source. What does it do in this case? It subtracts a portion of voltage from the whole input voltage: the resistor "creates" an opposing voltage drop across itself while the capacitor and inductor "create" an opposing voltage (a kind of emf). Resistors do this by throwing out (dissipating) energy while capacitors and inductors do it by taking energy from the excitation source, accumulating it into itself and setting it against the input source. In the first case there is a voltage drop while in the second case there is a voltage (emf).

    So, we can emulate these passive elements by replacing them with some other elements producing the same opposing voltage (having an opposite to the input voltage polarity when travelling along the loop). Then, we can modify or even create mirror active (negative) "copies" of these passive elements by replacing them with sources producing the same but now "helping" voltage (having the same as the input voltage polarity when travelling along the loop). This is the main idea of the substitution and inverse substitution theorem perfectly considered by Prof. Lutz von Wangenheim in his work: 
    https://www.researchgate.net/file.PostFileLoader.html?id=540dd638d039b1ee348b458f&key=d62e286c-fe94-4019-b22b-4b550b6c8bfa

    * Emulating by (varying) voltage. First, we may replace the original elements by varying voltage sources and this is the most natural way of making emulated capacitors and inductors (as they behave as varying through time voltage sources). Op-amp gyrator, multiplying, memcapacitive and meminductive circuits do it in this way. In these circuits, the op-amp output voltage represents the voltage across the according capacitor or inductor.

    In the case of the true negative resistor, the ordinary ohmic resistor is replaced again with a voltage source (exactly as in the case of gyrators and multipliers) but it has the same polarity as the input voltage source so that it adds an additional  voltage to the input voltage. For example, the negative impedance converter with voltage inversion (VNIC) is a dynamic voltage source emulating a negative resistor by adding a voltage that is equal to the voltage drop across a real ohmic resistor.

    It is interesting that we can change the properties of the ordinary constant voltage source by  properly varying its voltage (as in the attached picture below).
    The emulation by including an additional voltage source is the basis of the Miller theorem (see https://en.wikipedia.org/wiki/Miller_theorem#Applications).

    * Emulating by (varying) resistance. But a memristor can do the same by replacing the voltage by an equivalent voltage drop across a dynamic time-dependent resistor. Transistor gyrator and multiplying circuits do it in a similar way.

    It is interesting that we can change the properties of the ordinary ohmic resistor by properly varying its resistance. A good example of this technique is the creation of the negative differential resistor:
    https://en.wikibooks.org/wiki/Circuit_Idea/Negative_Differential_Resistance#General_considerations_about_creating_the_NDR

    So, to emulate passive elements (to create virtual elements), we may replace the elements behaving as resistors with (properly varying) resistors, and elements behaving as sources - with (properly varying) sources. But it seems we can do it by swapping these correspondences - replacing the elements behaving as sources with resistors, and elements behaving as resistors with sources... Am I right? Please, discuss.

    ------------------------

    I was inspired to ask this question mainly by the numerous discussions between me and Prof. Lutz von Wangenheim mostly in the questions below...

    https://www.researchgate.net/post/Are_electrical_sources_elements_with_static_negative_impedance_If_so_is_there_any_benefit_from_this_concept

    https://www.researchgate.net/post/Does_the_op-amp_in_all_the_inverting_circuits_with_negative_feedback_behave_as_a_negative_impedance_element_negative_resistor_capacitor_etc

    https://www.researchgate.net/post/Does_the_amplifier_in_negative_feedback_systems_possess_negative_impedance?

    ...and especially, by his idea about the inverse substitution theorem (IST) proposed by him in the question below:

    https://www.researchgate.net/post/Can_we_formulate_Kirchhoffs_laws_for_resistances_KRL_and_conductances_KGL_based_on_KVL_and_KCL/2

    Cyril Mechkov · Technical University of Sofia

    8. Virtually current-inverted (negative) resistance (3-4). Finally, we can go too far enormously strengthening the modified Miller's idea...

    Now, when you reach the point 3 (in the attached picture below), I begin "overopposing" you along the whole section 3-4. As usual, you are continuously increasing (make more positive) the voltage VIN of the input voltage source from point 3 to point 4 so that its IV curve continues translating to the right. But now I am extremely vigorously increasing the voltage VO so the composed VO-R IV curve extremely quckly moves (translates) to the right as well. As a result, the operating point A slides down along the new IV curve of the inverted positive resistance that is inclined (folded up) to the right and has a negative slope. You have the illusion the resistance R has become true negative resistance dR3 < 0.

    This idea is directly implemented in current-inversion negative impedance converters (INIC).

  • Peter Christoph Minkowski added an answer:
    Do you agree with Stephen Hawking's recent conclusion that black holes don't exist?
    Black holes don't exist. I published this many years ago. Cantor's Universe doesn't allow the concept.

    Stephen Hawking now came up with the same conclusion. Read: http://www.spektrum.de/news/es-gibt-keine-schwarzen-loecher/1222059

    In my opinion he is right this time. What is your opinion? Was he right then or is he correct now?
    Peter Christoph Minkowski · Universität Bern

    I suggest that no questions be encapsulate into a weblink , to consult on details attached to the question

  • Ellis D. Cooper added an answer:
    Is logical independence of the square root of minus one a consequence of arithmetic's incompleteness?

    In a formal arithmetical system, axiomatised under the field axioms, the square root of minus one is logically independent of axioms.  This is proved using Soundness and Completeness Theorems together. This arithmetic is incomplete and is therefore subject to Gödel's Incompletenss Theorems. But can it be said that the logical independence of the square root of minus one, is a consequence of incompleteness?

    Ellis D. Cooper · Endicott College

    TO Steve Faulker -- The term "real numbers" refers to a mathematical structure that is generally agreed to (by professional and amateur mathematicians worldwide) to be a model of the continuum, which is NOT a mathematical structure, it is a mental model with certain intuitively understood properties.  The mathematical structure is frequently constructed within one or the other axiomatic set theory. The first time I saw this was in a text by Patrick Suppes. The construction of the real numbers has also been carried out in a topos with additional structure, such as a natural numbers object. That is a terribly opaque way to do it, however. Dedekind's construction of the real numbers has been formalized, but the tower of constructions from whole numbers, to natural numbers, to integers, to rational numbers, and completion to the real numbers is well understood, and in more than one way. Take your pick.

  • Manuel Morales added an answer:
    Science vs Pseudoscience, what is the difference?

    With the discovery of Einstein's non-local hidden variables the findings show that the scientific method of predicting effects in order to obtain knowledge of cause is fundamentally flawed due to there being two mutually exclusive and jointly exhaustive causal variables in nature. Due to this discovery, the line between science and pseudoscience has now become significantly blurred.

    As defined in the Merriam-Webster dictionary:

    Science - knowledge about or study of the natural world based on facts learned through experiments and observation

    Pseudoscience - a system of theories, assumptions, and methods erroneously regarded as scientific

    If there was one attribute that clearly delineates the difference between science and pseudoscience what would it be?

    Manuel Morales · Institute of Prephysical Research

    I am surprised to see that so far researchers here at RG are unable to answer the question? Most curious indeed.

  • F. Leyvraz added an answer:
    How do you know whether a perfect disc falls heads or tails?

    If you have a perfect disc and flick it like a coin, how do you know which side came up? How can you know that statistically it is perfectly 50/50?

    F. Leyvraz · Universidad Nacional Autónoma de México

    ``The point I am making is that with perfect discs you cant see which side is which. If you mark the disc so you can see the outcome of repeated experiments, the disc is no longer perfect and you have broken the symmetry. You can only get 50/50 with unmarked discs, but you can't know its 50/50.'' Sorry to be mundane, but if you call, say, tails the side which is up at the beginning of the toss, then can you not simply observe the disk, say with a video camera, and deduce, from the continuity of the time evolution, which side it falls on?

    I do agree that this solution of your problem does not really shed light on the issue of the mixed state before observation (one usually calls measurement the process whereby a pure state become mixed. Finding out which among the possibilities in a mixed state is in actual fact the case, is rather a different issue). Perhaps we could say: looking only at the perfect disk after the toss tells us nothing, in order to know what actually happened we should look at the video, which would correspond to observation of the density matrix.

  • Ali BenMoussa added an answer:
    Is it necessary to plot the Norde function to extract the barrier height and series resistance?

    See above.

    Ali BenMoussa · Solar-Terrestrial Centre of Excellence

    For the estimation of the barrier height (at least) you could use optical (photocurrent) or CV methods. 

  • Tomasz Kawalec added an answer:
    Is it possible to observe sustained interference pattern from two independent laser source?

    Interference

    Tomasz Kawalec · Marian Smoluchowski Institute of Physics, Jagiellonian University

    If you use typical lasers like He-Ne, you need something like 10^-8 s resolution to observe the fringes. If you take two lasers and introduce a relative stabilization by means on an electronic circuit than the fringes are visible for hours (however the lasers are not independent).

    http://iopscience.iop.org/0143-0807/33/1/007/article

  • Shalender Singh added an answer:
    What do you think of the discovery of CERN and INFN about the velocity of neutrinos? It seems that they run faster than light
    Neutrinos run faster than light...
    Shalender Singh · Indian Institute of Technology Bombay

    I do not know validity of CERN experiments but superluminal particles exists very much in everyday life but they come up a particles going into past. So an electron moving faster than light is actually shows up as going into past, which means like a positron.

    The superluminal velocities are real and following paper gives a method to push electrons above the speed of light using existing accelerators and lab equipment: http://www.researchgate.net/publication/265643274_Extended_principle_of_relativity_beyond_speed_of_light_and_a_method_to_push_particles_beyond_the_speed_of_light

    Existence of superluminal velocities and the ability to measure them are two different problems. A frame of reference going above the speed of light will transform into 2 different frames of reference, one going in negative time and other in positive time. For example as I propose in another paper (not yet here), if an electron is pushed above the speed of light it will behave like a positron, which is an electron going into past. Also I propose that all positrons are electrons going above the speed of light, which shows up as going into past. As you can see in this paper, the Doppler Effect of radiation generated from a superluminal frame of reference shows up as negative frequency radiation, which is equivalent to Left hand em wave in vacuum. This radiation finds matter mostly transparent and the only way to detect is the reduction of entropy when it passes through matter.

  • Shalender Singh added an answer:
    Can information travel faster than the speed of light by pushing and pulling something extended between 2 points?
    Let's say an iron rod connects the moon to earth, and a machine connected to one side pulls and pushs it a bit to transmit some message, then a computer connected to the other side read those pushes and pulls. So can we affirm that the information travelled instantaneously between these 2 computers?
    Shalender Singh · Indian Institute of Technology Bombay

    The question is amazing and we cannot simplify or refute it by saying the rod is non-rigid OR the motion moves as molecular motion along the rod. Einstein never took those assumptions of elasticity of the matter OR motion as waves to deduce the special relativity. Let me answer your question as it is:

    Assuming the rod is completely rigid and motion is in-fact matter translation (not wave transmission), still the rod motion will transfer at the speed of light. Why is that? Assume that the 2 different ends of the rod are in the inertial reference frames with 0 relative velocity. For a distance observer also at 0 speed w.r.t. to both, the act of pushing the rod from moon, which implies acceleration will create a space-time voxel around the rod, which will compress the space-time around start of the rod and this voxel will move at the speed of light along the rod (In 4D space-time it is a fixed bundle of trajectories of the space-time bend), expanding when the deceleration is applied to stop the rod. If the rod is accelerated and then just bought to a uniform velocity and never stopped, the rod will appear to be shorter as it shows up in the Lorentz transformation.

    The reason Einstein described gravity and non-uniform motion as bend of space time was exactly because that. The space-time itself bends and warps, which means even the rigid bodies undergo transformation.

    On the other hand superluminal velocities are real and following paper gives a method to push electrons above the speed of light using existing accelerators and lab equipment: http://www.researchgate.net/publication/265643274_Extended_principle_of_relativity_beyond_speed_of_light_and_a_method_to_push_particles_beyond_the_speed_of_light

    Existence of superluminal velocities and the ability to measure them are two different problems. A frame of reference going above the speed of light will transform into 2 different frames of reference, one going in negative time and other in positive time. For example as I propose in another paper (not yet here), if an electron is pushed above the speed of light it will behave like a positron, which is an electron going into past. Also I propose that all positrons are electrons going above the speed of light, which shows up as going into past. As you can see in this paper, the Doppler Effect of radiation generated from a superluminal frame of reference shows up as negative frequency radiation, which is equivalent to Left hand em wave in vacuum. This radiation finds matter mostly transparent and the only way to detect is the reduction of entropy when it passes through matter.

  • Alessandro Schiavi added an answer:
    SCIENCE SLAM. How to do a good Science Slam talk on an advanced scientific thematique (for example, in solid state physics)?

    Please, share your experience on the above subject. Any materials, presentations or pieces will be of help.

    Alessandro Schiavi · INRIM Istituto Nazionale di Ricerca Metrologica

    Dear Cris,

    unfortunately I have not experience in that direction. Anyway your proposal is exciting, so I try to give you an idea on this topic.

    You can image the two most popular Zeno's paradoxes of  Achilles and the tortoise and of the arrow. In a certain way supersonic crack and phonons behave like that.

  • Johannes Gruenwald added an answer:
    Is there a book/paper reference to a physical explanation for point-like particles?

    Electron and quarks are defined as point-like particles.

    Johannes Gruenwald · Karl-Franzens-Universität Graz

    I think the only explanation for such an approximation is that these particles are very small compared to a macroscopic body and some integrals are just easier to solve if a Dirac delta functional can be used. If you treat those on a strict quantuum mechanical level (where nearly everything is very small) you don't have pointlike particles anymore but wave functions.

    So I guess there is no real paper or book where you can read that - it's more some "physical common sense" when treating such problems.

  • Cyril Mechkov added an answer:
    Are electrical sources elements with "static negative impedance"? If so, is there any benefit from this concept?

    The negative impedance concept is so attractive that some authors try to bring it on even the most basic electrical elements as voltage and current sources. See as an example the work of this Wikipedian (although it seems his own creation, it is assembled entirely by else's thoughts extracted from reputable sources):
    https://en.wikipedia.org/wiki/User:Chetvorno/work6#Negative_static_or_.22absolute.22_resistance

    Also, this viewpoint was presented by Simone Orcioni in the question below:
    https://www.researchgate.net/post/Does_the_op-amp_in_all_the_inverting_circuits_with_negative_feedback_behave_as_a_negative_impedance_element_negative_resistor_capacitor_etc

    As far as I understand, this "negative resistance viewpoint at voltage sources" is the following. A voltage source is connected to a load (a resistor)... so the voltage V (VG in he  Simone's figure) across them and the current I through them are the same... and therefore the ratio V/I (the resistance) for each element is the same (see the first attached picture below)... Thus the resistor has a resistance RL = V/I and the voltage source has a "negative resistance" RS = V/-I = -RL... so the sum of the two resistances (voltages, according to KVL) is zero... It sounds temptingly simple but...


    In this arrangement, there is only one "main" voltage source and one resistor (the load)... and this is the possibly simplest electric circuit still from 19-th century - a source driving a load. But the popular belief is that "negative resistance" is a "supplemental" concept... It implies another (supplemental, "helping") voltage source (BH in the second attached picture)... and this is not an ordinary constant but "dynamic" voltage source whose voltage is proportional to the current flowing through it (a 2-terminal current-to voltage converter)... and so it will act as a negative resistor with resistance -Ri. This negative resistance compensates another positive resistance Ri (e.g., the source internal resistance or the line resistance) thus giving as a result zero total resistance between the main source VIN and the load RL... and this 4-component circuit is reduced to the Simone's initial 2-component circuit (source and load)... The sense of this "trick" is that the unwanted resistance Ri (the voltage drop across it) is neutralized by an equivalent voltage:

    http://www.circuit-fantasia.com/circuit_stories/inventing_circuits/ser_nr_comp/ser_neg_res_comp.htm

    If this supplemental voltage source was an ordinary constant voltage source, it would still compensate the voltage drop across Ri... but only for one value of the current; maybe because of that they name this kind of "negative resistance" with the name "static negative resistance". Really, it can compensate also the relatively steady voltage drop across a constant-voltage nonlinear resistor (diode, LED, Zener diode, etc)... but this is just another special case...

    Note that, in contrast with an ordinary source, this exotic voltage source will not independently produce voltage if there is no input voltage VIN; it starts acting after the main (input) voltage source begins increasing its voltage from zero.

    IMO the word "resistor"/"negative resistor" has the meaning of something that resists/"helps" the current flowing through it... so it implies some initial current produced by another (main, input) voltage source... Therefore, this main source is simply a source, not a negative resistor... and maybe this viewpoint is just a misconseption as many others in the field of negative impedance phenomena?

    I would add here also the questions asked by Lutz Wangenheim: "Does it make sense to interpret this scenario as a connection of a positive and a negative resistance of the same value? More than that, are voltage and current directions of the voltage source in accordance with the DEFINIONS of a negative resistance? If this would be true, we could treat each voltage source in each circuit as a negative resistance, couldn´t we?"

    Cyril Mechkov · Technical University of Sofia

    Finally, I have asked the extremely interesting question about how to create virtual electrical elements in electronics:

    https://www.researchgate.net/post/How_do_we_create_virtual_electrical_elements_in_electronics_Are_they_really_elements_or_circuits

  • Cyril Mechkov added an answer:
    Does the op-amp in all the inverting circuits with negative feedback behave as a negative impedance element (negative "resistor", "capacitor", etc)?
    In all the op-amp inverting circuits (transimpedance amplifier, inverting integrator and differentiator, diode log and antilog converters, etc.), the op-amp compensates the voltage drop across the passive element (e.g., a resistor as in the attachment below) connected between the op-amp output and inverting input by adding an equivalent "mirror" voltage in series:

    https://en.wikibooks.org/wiki/Circuit_Idea/Voltage_Compensation

    As a result, the same current flows through the two elements - the resistor and the op-amp output, and the same voltage appears across them; so, they process the same energy and they have the same impedance. But while the first of them is a passive element that consumes energy (voltage) from the input voltage source, the second is an active element that adds the same energy (voltage) to the input voltage source. Then, if the first element has a "positive" resistance, the second element will show a negative resistance!

    https://en.wikibooks.org/wiki/Circuit_Idea/Voltage_Compensation#Negative_impedance_viewpoint_at_voltage_compensation

    So, we can conclude that in all the op-amp inverting circuits, the combination of the op-amp and the power supply actually acts as an element with negative impedance that neutralizes the positive impedance of the element connected between the output and the inverting input. As a result, the whole combination of the "positive" element (the resistor R in the picture) and negative element (the supplied op-amp) behaves just as... a piece of wire with zero impedance!

    From this negative impedance viewpoint, in the circuit of a capacitive integrator the op-amp is a "negative capacitor" producing the voltage Vc, in a diode log converter - a "negative diode" producing the voltage Vf, etc.

    It is interesting to compare this negative "resistor" with the true negative resistance circuit (voltage-inversion negative impedance converter - VNIC)...

    https://en.wikibooks.org/wiki/Circuit_Idea/Revealing_the_Mystery_of_Negative_Impedance
    Cyril Mechkov · Technical University of Sofia

    Finally, I have asked the extremely interesting question about how to create virtual electrical elements in electronics:

    https://www.researchgate.net/post/How_do_we_create_virtual_electrical_elements_in_electronics_Are_they_really_elements_or_circuits

  • Cyril Mechkov added an answer:
    Can we formulate Kirchhoff’s laws for resistances (KRL) and conductances (KGL) based on KVL and KCL?

    In the question below, we have been discussing if voltage sources possess negative resistance: 

    https://www.researchgate.net/post/Are_electrical_sources_elements_with_static_negative_impedance_If_so_is_there_any_benefit_from_this_concept

    This idea is proposed in a series of reputable sources cited in the Wikipedia work below:

    https://en.wikipedia.org/wiki/User:Chetvorno/work6#Negative_static_or_.22absolute.22_resistance

    It actually means to extend the scope of Ohm's law by applying it to the two kinds of electrical sources - voltage and current source.

    Considering the ratio V/I = R as a static negative resistance. In the basic Ohm’s arrangement, a voltage source is connected to a load (a resistor). The voltage V across and the current I through them are the same as magnitudes. As a result, the ratio V/I (the resistance) for each element is the same what is known as Ohm’s law - R = V/I. However, while the voltage across and the current through the load have the same signs, in the case of the source they are opposite. Therefore, the resistor has a “positive” resistance R while the voltage source can be considered as having a negative “resistance" -R, and the sum of the two resistances is zero.

    Considering the ratio I/V = G as a static negative conductance. In this dual Ohm’s arrangement, a current source is connected to a load (a resistor). The current I through and the voltage V across them are the same as magnitudes. As a result, the ratio I/V (the conductance) for each element is the same what is a dual form of the Ohm’s law - G = I/V. However, while the current I through and the voltage across the load have the same signs, in the case of the source they are opposite. Therefore, the resistor has a “positive” conductance G while the voltage source can be considered as having a negative “conductance " -G, and the sum of the two conductances is zero.

    Here, I propose to develop this idea further as Kirchhoff done with Ohm's law in the distant 1845. Here are my speculations...

    Converting the Kirchhoff’s law for voltages (KVL) to a law for resistances (KRL). KVL says that the sum of the voltages E (emfs) and the voltage drops V is equal to zero:

    -E1 + -E2 + -E3 + ... V1 + V2 +V3 + ... = 0

    If we formally divide this “voltage” equation by the current I

    -E1/I + -E2/I + -E3/I + ... V1/I + V2/I +V3/I + ... = 0

    and apply the Ohm's law for emfs and voltage drops, we will obtain

    -R1 + -R2 + -R3 + ... R1 + R2 +R3 + ... = 0

    where the voltages E are represented by the negative “resistances” -R1, -R2, -R3..., and the voltage drops V1, V2, V3... – by the “positive” resistances R1, R2, R3. So, we can name this “resistance” equation Kirchhoff’s law for resistances (KRL):

    The sum of voltage-type negative resistances connected in series in a closed loop is equal to the sum of positive resistances.

    Converting the Kirchhoff’s law for currents (KCL) to a law for conductances (KGL). KCL says that the sum of the currents entering/exiting a node is equal to zero:
    -I1 + -I2 + -I3 + ... I4 + I5 +I6 + ... = 0

    (here I suppose the currents I1, I2 and I3 are produced by current sources while I4, I5 and  I6 are consumed by resistor loads)

    If we formally divide this “current” equation by the voltage V

    -I1/V + -I2/V + -I3/V + ... I4/V + I5/V +I6/V + ... = 0

    and apply the dual Ohm's law, we will obtain

    -G1 + -G2 + -G3 + ... G4 + G5 +G6 + ... = 0

    where the source's currents are represented by the negative “conductances” -G1, -G2, -G3..., and the load's currents – by the “positive” conductances G4, G5, G6. So, we can name this “conductance” equation Kirchhoff’s law for conductances (KGL):

    The sum of current-type negative conductances connected in parallel to a node is equal to the sum of positive conductances.

    Converting the Kirchhoff’s laws to a law for powers (KPL). Finally, we can extend this modifying idea to powers. If we formally multiply the “voltage” equation above by the current I

    -E1*I + -E2*I + -E3*I + ... V1*I + V2*I +V3*I + ... = 0

    or, if we multiply thе “current” equation above by the voltage V

    -I1*V + -I2*V + -I3*V + ... I4*V + I5*V +I6*V + ... = 0

    we will obtain

    -P1 + -P2 + -P3 + ... P4 + P5 +P6 + ... = 0

    We can name this derivative “power” equation Kirchhoff’s law for powers (KPL)... and actually this is the well-known power balance:

    The sum of negative powers (in a loop or at a node) is equal to the sum of positive powers.

    I would like to inform that the idea to modify Kirchhoff’s laws in such a way was born during heated discussions mainly between Prof. Lutz von Wangenheim and me.

    Cyril Mechkov · Technical University of Sofia

    Finally, I have asked the extremely interesting question about virtual elements:

    https://www.researchgate.net/post/How_do_we_create_virtual_electrical_elements_in_electronics_Are_they_really_elements_or_circuits

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