• Zol Bahri Razali added an answer:
    What is the basic physical explanation of the acceptor-bound-exciton peak in PL for ZnMgO?

    I have got references claiming acceptor peak at 3.33 eV [J.C. Fan, C.Y. Zhu, B. Yang, S. Fung, C.D. Beling, G. Brauer, W. Anwand, D. Grambole, K.S. Wong, Y.C. Zhong, Z. Xie, C.C. Ling, J. Vac. Sci. Technol., A 29, 03A103-4 (2011)]for ZnMgO. However,there are also several references claiming this peak at 3.33 eV due to donor-bound exciton peak. 

    Kindly provide me some basic physics behind it.

    Zol Bahri Razali · Universiti Malaysia Perlis

    Good question. I will be back later to answer the question/s

  • Closed account added an answer:
    Is it possible to electrically insulate an aluminum block by fabrication?

    Their is an aluminum block that is internally hollow. It has to be electrically insulated but thermally active.

    Is it to possible to electrically insulate it by depositing a layer of Aluminum Nitride or Silicon carbide or magnesium oxide.

    If yes, what should be the fabrication process and what should be the thickness of deposition.

    Any information or experience with regards to the subject is welcomed.


    @ R.Brian Peters

    Thank you 

  • Pavan Kumar added an answer:
    What are the limitations when using the method of Williamson Hall for research into the size and strain in nanowires GaN?
    Can I apply this method in general for such objects?
    Pavan Kumar · North Carolina Agricultural and Technical State University

    I'm also using W_H analysis for my samples. I found one journal based on W-H analysis on GaN nanowires

    Title: Macro- and micro-strain in GaN nanowires on Si(111)

  • Daniel Martinez Krahmer added an answer:
    What are the steps to make a good review of scientific papers?
    What are the steps to make a good review of scientific papers? Who can advise me? Can we use a software for review of a paper? If so, is there a free software?
    Daniel Martinez Krahmer · Instituto Nacional de Tecnologia Industrial

    I forgot something very important: the using of design of experiments (DOE) and the application of estadistics to analize the results too.

  • Shaban Ahmed Ali Abdel-Raheem added an answer:
    In what fields of study can we utilize factorization in polynomial rings?
    I am searching for recent studies on other fields of study, like biology, chemistry, engineering, physics, nanotechnology, etc, on which we can find connections among factorization domains in algebra, divisio algorithm, etc.
  • Sumit Kumar Rajdhania added an answer:
    Which is more elastic steel or rubber and why?
    I know that steel has large elasticity but don't know why.
    Sumit Kumar Rajdhania · Indian Institute of Technology Delhi

    Steel , #support @krishna Garg sir answer

  • James R Knaub added an answer:
    Is the scientific method natural to humans, or does it require a special effort? What about other animals?
    Take the average person you meet - how do they make decisions? What about evolution - has the scientific method ever had any influence on genetic mutation, or has any other aspect of evolution had any influence on living beings?
    James R Knaub · N/A

    Edward -

    The "What about other animals?" caught my attention, and reading through the other answers first, I think that Aliza came closest to what I was thinking. You do see the basics of experimentation by other animals. A lot if it had to be accidental at first, like a large bird dropping a clam on a rock to open it, or just having fun, like a parrot or similar bird I saw had taught itself to use a peanut shell as a bucket from which it drank. But other primates use tools, and some examples of basic elements of scientific methodology have to be found in large numbers in other animals.

    Perhaps the disappointment we feel is that humans have learned something about 'perfecting' the scientific method, yet often seem to avoid it. However, I think that many use it more than they realize. Someone who didn't want to take high school algebra may claim for the rest of their lives that they "never used it," without being fully conscious of the many thousands of subtle uses of logic they made that may have been inspired by abilities they honed in that experience with algebra. However, you could say this is more related to the Ancient Greek Philosophy of logic, which fell short of full science or they would possible have gone beyond the 'four elements.' But it is something and it gave modern science a start.

    However, it is true that there is a great deal of interference with science in modern society. I heard or read that in North Carolina, the legislature decided that climate change was not to be considered in official documents, due to its inconvenience, so in effect it was outlawed. At one point the US Bureau of the Census, trying to avoid undercounting minorities, was criticized by Congress, at least one member going so far as to say that "sampling" was some kind of magic, not to be trusted. As a statistician, I was very embarrassed for the US. I've seen office politics that I had to struggle with and often lose against while trying to take the most clearly correct actions. The foolishness, irrationality, and too often selfish and hateful nature of humans can sometimes drown rational and socially progressive views, which you would think would contradict the evolutionary progress that was part of the inquiry Edward made. But perhaps we are just overreacting when we see it that way. Perhaps when we see irrational behavior (or otherwise disappointing behavior that I realize I mixed in here) we weigh that too heavily, and do not give enough credit to the scientific nature that is present in humans and other animals. It isn't perfect, but it's there.


  • Salaisargunan S P added an answer:
    Can you explain about wall boundary?

    Hi, what is difference between non-slip and slip boundary at wall... give a physical and mathematical details about that....

    Salaisargunan S P · Pusan National University


  • Amuda Afees 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.

    Amuda Afees · Usmanu Danfodiyo University Sokoto

    the manner and ways you present your lessons matters alot  and can help you reduced the adverse effects of other variables that affect students achievement in physics.

  • Gert Nolze added an answer:
    What is the concept of reciprocal lattice? What is the need of using reciprocal lattice?

    I wanna to know the basics of the reciprocal lattice and use of it in solid state physics.

    Gert Nolze · Bundesanstalt für Materialforschung und -prüfung

    "A point in reciprocal lattice represent a plane in real space"...is not really correct since only a direction (hkl) in reciprocal space represents a plane in real space. The points in reciprocal space are described by Laue indices hkl which dont have to be coprime whereas lattice planes are described by Miller indices (hkl) where h,k and l must be coprime. The same happens with lattice directions [uvw] and lattive points :uvw:. First are defined to be coprime whereas the latter describe any lattice point by a vector and dont have to be coprime.  

  • Andrew Wutke added an answer:
    A question on Time as an emergent property
    Time can be viewed as an emergent property : whenever any change occurs anywhere in the universe - in other words whenever the state space of the universe undergoes any change - then Time itself happens and 'notches up' one tick (at least in the 'neighbourhood' of the change, which is a separate discussion.)

    But isn't this circular reasoning ? For a change in state space to be able to occur in the fist place, isn't the pre-existence of something like time a prerequisite ?

    The only way out of this conundrum is that all elementary state space changes must happen out of time, i.e. instantaneously (with a delta time = 0.) But this would then require the superimposed coexistence of 2 elementary state spaces. Can this happen ? We could probably engineer a situation where the Pauli exclusion principle would then be violated. This would tend to prove that Time as an emergent property cannot be the whole story?

    Any comments?
    Andrew Wutke · Thales Group


    I agree that time as an emergent property is a step in the right direction.

    The next step is that there is no universal emergent tick. Simply there is no time at all.

    Things change interact in one common reality. Some of them are selected as clocks to compare with other states. All I see is a vast number of changing coexisting states of coexisting objects.

    I see some relevance of the concept of traffic. It emerges from the properties of vehicles that move. There is no point you can put your finger and say this is traffic. You finger will always point to a vehicle. Traffic is an abstract concept, like time it "flows" and you can calculate flow rate (number of cars in my street per number of cars in the reference  street both between dawn and dusk) .

    Newton's concept of absolute time has not been abolished as it is claimed, but it has been multiplied and shifted to each inertial frame. We need one more step to abolish it altogether and free ourselves from this entanglement.

    But change as such, and memory of past states is a bit of a mystery so there is plenty of interesting problems yet to be solved by science.

  • Johan Frans Prins added an answer:
    Is time quantized?
    Each time a new class of lasers was allowed to produce shorter light pulses, people were wondering whether a time quantization would be observed. The smallest possible quantization is Planck's time 10^-44 s. Some nuclear resonances have been reported having an energy width suggesting a Fourier transform limited duration of 10¨-26s.
  • Rana Al Khaldi added an answer:
    Why the conductivity of Metal increase with decrease in temperature, semiconductor increase with increase in temperature and alloys remains same ?
    Is it due to the following reasons?
    Metals : Due to the formation of more free electrons
    Semiconductors: Due to the formation of Cooper pairs and hence the creation of Phonon field
    Alloys: No Free electrons or Phonon field created
    Rana Al Khaldi · University of Dammam

    Dear Kevin A Shaw.. your answer is correct except this information:

    "We usually view these carriers as electrons because in metals the carrier is the electron."

    According to Hall effect Experiment,  the carrier in metal could be positive charge or negative. So, any positive value of RH it means the carrier is positive"hols not electron" and it listed in Tables.

  • Matts Roos added an answer:
    Is there any evidence m_neutrino is not 0.09161 eV/c^2?
    My attempt at theory indicates m_neutrino ~ 0.09161 eV/c^2 - for all three neutrinos. The relevant result is (m_neutrino)*(m_tauon) ~ {(m_electron)^2}*{(alpha)^(3/2)}. Here, alpha is the fine-structure constant.
    I believe the result is consistent with S. Thomas, et. al., http://arxiv.org/abs/0911.5291 and roughly consistent with page 46 of J. Beringer, et. al., http://pdg.lbl.gov/2012/reviews/rpp2012-rev-neutrino-mixing.pdf .
    Perhaps people know of more data - favorable or unfavorable to the above result - regarding neutrino masses?
    (The attachment provides more information about the theory. See, especially, page 6, Table 2, items (12) and (14).)
    Matts Roos · University of Helsinki


    I agree with the astrophysics-based observations suggesting an upper limit of ~0.23 eV on the sum of the neutrino masses.

    The 2014 issue of the Review of Particle Physics (Chinese Physics C, vol 38, nr 9, September 2014) recommends the upper limit 2 eV for the mass of the e-neutrino, the other species having mass limits in the MeV range.

  • Giuseppe Tattara added an answer:
    Do only publications with an ISI impact factor prove the quality and originality of our work?
    Giuseppe Tattara · Università Ca' Foscari Venezia

    publication in peer reviewed journals is assumed to be the common way for gaining approval for a research work, but in my experience, it is not always so. Some reviews are just meaningless), pretending the author's opinion is in line with that of the reviewer or asking to refer compulsory to some scholarly articles (the reviewer itself?). I don't think the impact factor is always an important quality factor.

  • Stephen Crothers added an answer:
    In spacetimes, what is the most general metric of the existing ones?

    I read many articles about space-times. Most authors consider these spaces as warped product manifolds I×M where I is an open connected interval of the real line and M is a Riemannian manifold. Minkowski space-time, anti-de Sitter, and the Einstein static universe are well-known examples of such space-times.

    Many authors considered a general metric of these three examples and construct the so-called static space -times.

    My question is: Is there a generalized metric on all space-times?

    Note that my question is not about the most generalized metric but about the generalized metric of the existing ones.

    I want to bank up the existing metrics in one generalized metric.

    Thanks in advance

    Stephen Crothers · Alpha Institute of Advanced Study

    Sameh Shenawy - All the static/stationary metrics can be generated easily from a general expression. See Appendix A (Equation A17) of the following:

    General Relativity: In Acknowledgement Of Professor Gerardus ‘t Hooft, Nobel Laureate,

  • Shaban Ahmed Ali Abdel-Raheem added an answer:
    How can I measure the Refractive Index (RI) for new synthesized metal complexes in a solution state?
    Other than Ellipsometry or Abbe refractometer, it should be easy method and precise value.
  • Ciprian G. Gal added an answer:
    Can anybody explain the behaviour of my new dynamical system? Is there chaos?

    I have asked a similar question before. I thank those participated and helped; however I didn’t find my answer. Consider the system described in the following ODEs:
    dx/dt = 1 +z^2 -w^2 -0.01x
    dy/dt = 2zw -0.01y
    dz/dt = -1 +x^2 -y^2 -0.01z
    dw/dt = 2xy -0.01w
    Can anybody please simulate the above system and tell me what kind of solution it has? With my simulations, that system is sensitive to initial conditions and has some strange trajectories I cannot understand. It seems that trajectories go to infinity, but they always come back.
    Is this kind of behavior familiar for some one?
    Please see the attached figure. Note that in that, I have simulated the system for 100 sec and my initial conditions have been [1, 1, -1, 1].

    There are some points I should add:
    1. I used ode113 in MATLAB. It uses and an integrator with adaptive step-size.
    2. This system has come from an unpublished paper which we have written (see sprott.physics.wisc.edu/pubs/paper389.pdf). The original system is:
    dM/dt = 1 +L^2 -0.01M
    dL/dt = -1 +M^2 -0.01L
    and I have considered M & N as complex variables (M = x + iy & L = z + iw).


    There are some more additional points I should add:
    1. This system is an excellent example to challenge the power and accuracy of different integrating methods. Just simulate it and run it for100, 1000, and 10000 sec. Observe time series and some state plots (I recommend seeing x time series and the trajectory in x-y plane). You can see that different methods and step-sizes can affect the results noticeably.
    2. This system is obviously dissipative. However I don’t think being dissipative ensures being bounded for a system (am I right?).
    3. I have attached extra materials to this question (see Dance of the ballerinas.rar). I think they are interesting, but I don’t know why we can see such results and how we can interpret. I appreciate any help and possible collaboration on that.

    Ciprian G. Gal · Florida International University

    You have to think about these questions:

    1. Does your system have an energy which can be written down and which is dissipated in some sense?

    2. Is there a bounded absorbing set for your system?. Note that by definition a bounded absorbing set (or a ball of radius independent of B) is a set/ball to which all trajectories emanating from a bounded set B of (initial) vectors tend to as time go to infinity. 

    In either case if this is something you want to achieve in a first step, both can help you prove the existence a maximal bounded attractor which consists of all those closed (and bounded) beautiful trajectories displayed in your picture. Both of the points in 1), 2) can help describe your system dynamically in a more precise way.

  • Jacek Hoffman added an answer:
    How can one distinguish spectral lines for waves developed using interference?

    Can anybody help me to categorise the original spectral lines of an interfered wave from the spectral lines of a developed wave using interference. I use here Thorium and Uranium spectra as primary.


    I've used diatomic Thorium and Uranium molecules to study the molecular spectrum of molecular species in gas clouds. The rotational transitions of these molecules will emit photons which as a probability to interfere with the surrounding clouds and in turn result in a distorted spectrum of the system. If as an end user, I capture these distorted spectrum, how can I categorise which molecules contribute to this spectrum?  

    Jacek Hoffman · Institute of Fundamental Technological Research

    In either case mentioned above there should be no fundamental problem with identification of molecules. The shapes of spectra could be a bit distorted but their wavelength position remains which would allow identification by simple comparison of spectra with standard. More detailed and precision comparison may be used when one want to obtain the cloud temperature. As an example take a look at http://www.specair-radiation.net/  for vibrational spectra of air components . There exists similar codes developed by scientists in many fields.

  • Behnam Farid added an answer:
    What is the minimum carrier density in Mott Insulator?

    Minimum carrier density in Mott Insulator.

    Behnam Farid

    You are welcome Rajesh.

  • Neal King added an answer:
    How is it possible to have momentum in a situation of perfectly static electric and magnetic fields?

    The Poynting vector P  = E X H is non-vanishing for a perfectly static situation like a charged capacitor with a magnetic field applied perpendicular to the electric field between its plates.

    How can static fields carry momentum? Either our understanding of fields is wrong or we have to redefine momentum!

    Neal King

    The angular momentum of the coil can easily be calculated to be:

    8LS^2 (mγ/q)(Bo/μo)

    The ratio of this AM to the hidden P is:

    2mγc^2/(qEo) ~ 1000 (km)/Eo[V/m]

    This is a pretty big 'lever arm' for practical values of Eo; which gives the impression that the EM field is much better at radiating away angular momentum than linear momentum.

  • Mohamed Hakim added an answer:
    Is there a physical principle states that an object reach to lower energy levels with the least amount of work [work W =F( force )*d(displacement)]?

    For example, consider if a ball falls down the inclined plane, is there a law to prove that the ball goes straight pathways and not another?

    Mohamed Hakim · steg tunisie

    la réponses est probabiliste voir stochastique

  • William Lentz added an answer:
    I need a very inexpensive optical test pulse for my 532 nm lidar. What (LED/laser) can be driven sub-nanosecond?
    I need to know what led or laser diode can be driven with sub-nanosecond pulse width. I don't mind building my own driver. Commercial units are far to costly.
    William Lentz · Marina Photonics Inc.

    It is my understanding that the structure of the led determines the rise time.    I can build 30 picosecond drivers, but the led determines the rise time.    I am looking for a part number for a 100 ps rise time or faster led.  

  • Brahim Bouali added an answer:
    Can we find an answer to the quantum theory paradox?

    Einstein was never happy with the outcome of quantum theory. We tend to accept the paradox of not seeing in order to understand. What if Einstein's intuition was right? What if we can see the systematicity behind what seems unsystematic? Can we predict the position of a particle while making the forbidden-observing?

    Brahim Bouali · University of North Carolina at Charlotte

    dear all,

    I m planning to design an ESP course for Quantum Theory. I believe that ESL has to move from the easiness of skilled-based approaches that does not help second language learners see the difference between Newtonian classical physics with modern physics to a more efficient content-based approach that teaches basic concepts in QT while focusing on structural and functional aspects peculiar to QT such as metaphors, phrasal verbs, if-clauses etc. The problem is that I have always pursued Math as a hobby therefore I do not have the expertise nor the credentials to attest for the accuracy of information. People in the English department are not familiar with Quantum theory let alone  the complexity of the equations. Is there any one who wills to check my thesis if the department agrees to let me do it... 

    Any suggestion would be very helpful!

  • S K Mohapatra added an answer:
    Is a different model used for Ge-MOSFET in TCAD Sentaurus?

    Difference in physics part for Si and Ge MOSFET simulation in Sdevice.

    S K Mohapatra · National Institute of Technology Rourkela

    Dear A Paul

    As per Prashanth Paramahans Manik answer to me same model is applicable for Ge. I have not worked using Ge. But I have used GaAs material with same model.


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