• Gunther Kletetschka added an answer:
    8
    Can seismic/impact energy lead to an increase in temperature at the mantle/core boundary?
    If there is a 10 Mtons surface explosion - how much temperature increase can be expected at the core/mantle boundary directly under the surface explosion? S-waves do not penetrate liquids and therefore some of the energy should be absorbed at the core mantle boundary.
    Gunther Kletetschka

    In case of photon radiation there is a complex part of magnetic permeability and permittivity that define how much energy is lost on the interface. What would be equivalent of this for seismic waves? Phase shifted S waves?

  • Farzad Pashmforoush added an answer:
    6
    How can I calculate the force experienced on a ferromagnetic particle (say 500 mum Fe particle) by a bar magnet which is at suppose 10mm distance?
    Assume parameter if required x y z which is not given in the question.
    Farzad Pashmforoush

    Check "Magnetic field-assisted finishing - Wikipedia".

     There are useful formulas for calculation of magnetic force on a particle. The force is dependent on magnetic field intensity (H) and its gradient, volume and magnetic susceptibility of the particle, 

  • prof V.S Muralidharan added an answer:
    90
    What do you think of MSc and PhD theses written in languages other than English?
    For non-native speakers it can be easier to write in their mother tongue. Moreover, pride in ones language can play a role. However, the language of science is English and writing science in other languages has, therefore, drawbacks. I wonder how this issue is navigated internationally.
    prof V.S Muralidharan

    i received an e mail stating that

  • Nash Chu added an answer:
    24
    Is it possible to create the plasma in vacuum ?

    We have two electrodes in a vacuum chamber and we applied a d.c. voltage . plasma formation is possible or not ? what will be the effect if we apply an a.c. voltage source ? what should be the minimum distance between the electrodes to form an plasma.

    Nash Chu

    @Charles Hirlimann. Thank you for your correction to consider the quantum mechanic effect of vacuum.  I was wondering if there were some results in high energy experiments to prove that we can create plasma from absolute vacuum.  

  • Paul F. Gentle added an answer:
    18
    How can we manage cross-border illegal trade?

    Control and manage cross-border trade at physical cross-border regions.

    Paul F. Gentle

    In some ways countries which tend not to enforce laws against murder and other assault within their own borders can be thought of as frontiers, rather than countries.  The USA knowingly does not regulate trade or immigrants from some countries but is hard on more educated immigrants.

  • Parviz Parvin added an answer:
    6
    How we can generate attosecond laser pulses ?

    please give the principle and different techniques ? thanks

    Parviz Parvin

    According to one cycle phenomena, the wavelength attributing to atto second pulse lies in VUV or  Xray spectral region while that of fs pulse may be in be in NIR. IS NOT IT?

  • Muhammad Aslam Baig added an answer:
    5
    Why are s to s transitions allowed in He-Ne laser ?

    As the atomic selection rules says that s to s transitions are not allowed i.e. there must be a change of the angular momentum ?

    Muhammad Aslam Baig

    A. Kani has given the correct answer, the s-s transitions are optically forbidden but such transitions can be collision-ally induced.  However, the s to s transitions can also be accessed via two-photon excitation.  

     The He-Ne laser works because one of the excited level in Ne, 2p54s lies nearly at the same energy of 1s2s 3S1 and 1S0 levels of helium and as a result the helium atoms gets excited due to energy transfer. The laser action is between the levels of neon, not  that of helium. There are a number of possible transitions for which laser can be made, either in the Red region at 633 nm or in the green or yellow colors.

    The details of these transitions can be found in any simple books on laser or atomic physics such as be Demtroeder or Selvast etc.

    Aslam      

  • Jerry Rhee added an answer:
    99+
    What evidence would be needed to prove Nature is intrinsically mathematical?

    As opposed to mathematics being an invention, what evidence would convince us that mathematics is there already in Nature?

    Jerry Rhee

    For this case, the evidence would be in futuro, dependent on the “consensus opinion fated to be agreed upon by all who investigate”.

    For example, when genuine doubt is replaced by belief in the working hypothesis (phi spiral abduction) as to what the following represents; a convergence between the sign and the object.  For example, being able to predict with mathematical tools and interpretant standards, what the sign would be in the next corneal spiral.

  • Andrea Addazi added an answer:
    2
    If the coupling constant between inflaton field and scalar curvature is nonzero, what are the physical results?

    Researchers in the fields of cosmology and gravitation, which are also expert at high energy physics .

    Andrea Addazi

    If I understand the question (assuming 4D and initial condition usually consider for ordinary inflation), you are describing a scalar-tensor theory. These theories can be mapped to f(R)-models. If you start from an f(R), through a conformal transformation you just obtain a scalar degree of freedom coupled with the metric as in scalar-tensor models. Starobinsky model is nothing but a f(R)=R+R^{2}, inflaton is just the extra scalar degree of freedom propagating in this model. You can also obtain the precise potential in this case.  

  • Henri Cloetens added an answer:
    3
    What does this equation mean?

    I have come out with my own equation(I have no idea whether it is new) for pie : π = √2/2 x n x √((1-cos(dΘ)), where n is the number of triangles in the circle, and  dΘ is the angle of the triangle that is -->0. Ok, now, say, I put n = 1440, so dΘ will be 360/1440 = 0.25, and put it into the equation, i will get  π= 3.141590118…; if I put n=2880, so dΘ will be 0.125, putting it into the equation, I will get π=3.141591603.., if I put n=5760, so dΘ will be 0.0625, putting it into the equation, i will get π= 3.141592923..., we know π= 3.141592654..,but i can never really get the n and dΘ to give that answer. Anyone can come out with some good idea??

    Henri Cloetens

    Dear Mason,

    I dont know. I took this from you.

    Best Regards,

    Henri.

  • Raghda Abogabal added an answer:
    1
    What is the concept of Fermi velocity?

    See above.

    Raghda Abogabal

    At absolute temperature the fermions electrons still move with a kinetic energy corresponding to a fermi level.

  • Roman Puzniak added an answer:
    4
    Discontinuity of type-II superconductor magnetic hysteresis loop
    Not very often we can see magnetic hysteresis loops of type-II superconductors in their entirety. The published figures mostly present only their upper and lower branch, but their "ends" are usually outside the figure. Yet, in situation when the exciting field amplitude falls between Hc1 and Hc2, the discontinuity (jump) is observed in sample magnetization, even its sign is changed. Anything like this never happens in ordinary magnetic materials: here the two branches are always coinciding at the return point, i.e. at the maximum of the external field. What could be the possible reason for such an amazing behavior?
    Roman Puzniak

    According to me the best answer for you question is given in the two following papers:

    - Magnetization of Hard Superconductors, C. P. Bean, Phys. Rev. Lett. 8, 250 (1962),

    - Magnetization of High-Field Superconductors, C. P. Bean, Rev. Mod. Phys. 36, 31 (1962).

    If you want to find analogy with magnetic materials you should take into consideration that in the H-T phase diagram of superconducting materials there is an additional line to the Hc1(T) and Hc2(T). It is so called irreversibility line, Hirr(T), located between Hc1(T) and Hc2(T). In the magnetic field Hc1, the vortices enter superconductor. However, in the magnetic field bellow Hirr, they are pinned – their arrangement and thus magnetization of superconducting material depends on the history. The hysteresis loops mentioned by you are recorded in magnetic field below Hirr, not above Hirr. To find analogy with magnetic materials you should refer to the minor hysteresis loop of magnetic material, where the irreversible domain wall motion takes place. For the hysteresis loop of type-II superconductors recorded in the field above Hirr the two branches are coinciding at the return point, i.e. at the maximum of the external field, as it is in the case of ordinary magnetic materials.  

  • George Stoica added an answer:
    11
    What is the degradation scale in the higher education worldwide?
    In my previous question I suggested using the Research Gate platform to launch large-scale spatio temporal comparative researches.
    The following is the description of one of the problems of pressing importance for humanitarian and educational sectors.
    For the last several decades there has been a gradual loss in quality of education on all its levels . We can observe that our universities are progressively turning into entertaining institutions, where students parties, musical and sport activities are valued higher than studying in a library or working on painstaking calculations.
    In 1998 Vladimir Arnold (1937 – 2010), one of the greatest mathematicians of our times, in his article “Mathematical Innumeracy Scarier Than Inquisition Fires” (newspaper “Izvestia”, Moscow) stated that the power players didn’t need all the people to be able to think and analyze, only “cogs in machines,” serving their interests and business processes. He also wrote that American students didn’t know how to sum up simple fractions. Most of them sum up numerator and denominators of one simple fraction with the ones of the other, i.e. as they did it, 1/2+ 1/3 according to their understand is equal to 2/5 . Vladimir Arnold pointed out that with this kind of education, students can’t think, prove and reason – they are easy to turn into a crowd, to be easily manipulated by cunning politicians because they don’t usually understand causes and effects of political acts. I would add, for myself, that this process is quite understandable and expected because computers, internet and consumer society lifestyle (with its continuous rush for more and newer commodities we are induced to regard as a healthy behavior) have wiped off young people’s skills in elementary logic and eagerness to study hard. And this is exactly what the consumer economics and its bosses, the owners of international businesses and local magnates, need.
    I recall a funny incident that happened in Kharkov (Ukraine). One Biology student was asked what “two squared” was. He answered that it was the number 2 inscribed into a square.
    The level and the scale of education and intellectual decline described can be easily measured with the help of the Research Gate platform. It could be appropriate to test students’ logic abilities, instead of guess-the-answer tests which have taken over all the universities within the framework of Bologna Process which victorious march on the territories of former Soviet states. Many people can remember the fact that Soviet education system was one of the best in the world. I have therefore suggested the following tests:
    1. In a Nikolai Bogdanov-Belsky (1868-1945) painting “Oral accounting at Rachinsky's People's school”(1895) one could see boys in a village school at a mental arithmetic lesson. Their teacher, Sergei Rachinsky (1833-1902), the school headmaster and also a professor at the Moscow University in the 1860s, offered the children the following exercise to do a mental calculation (http://commons.wikimedia.org/wiki/File:BogdanovBelsky_UstnySchet.jpg?uselang=ru):
    (10 х 10 + 11 х 11 + 12 х 12 + 13 х 13 + 14 х 14) / 365 = ?
    (there is no provision here on Research Gate to write square of the numbers,thats why I have writen through multiplication of the numbers )
    19th century peasant children with basted shoes (“lapti”) were able to solve such task mentally. This year, in September, this very exercise was given to the senior high school pupils and the first year students of a university with major in Physics and Technology in Kyiv (the capital of Ukraine) and no one could solve it.
    2. Exercise of a famous mathematician Johann Carl Friedrich Gauss (1777–1855): to calculate mentally the sum of the first one hundred positive integers:
    1+2+3+4+…+100 = ?
    3. Albrecht Dürer’s (1471-1528) magic square (http://en.wikipedia.org/wiki/Magic_square)
    The German Renaissance painter was amazed by the mathematical properties of the magic square, which were described in Europe firstly in Spanish (the 1280s) and Italian (14th century) manuscripts. He used the image of the square as a detail for in his Melancholia I painting , which was drawn in 1514, and included the numbers 15 and 14 in his magic square:

    16 3 2 13
    5 10 11 8
    9 6 7 12
    4 15 14 1

    Ask your students to find regularities in this magic square. In case this exercise seems hard, you can offer them Lo Shu (2200 BC) square, a simpler variant of magic square of the third order (minimal non-trivial case):

    4 9 2
    3 5 7
    8 1 6

    4. Summing up of simple fractions.
    According to Vladimir Arnold’s popular articles, in the era of computers and Internet, this test becomes an absolute obstacle for more and more students all over the world. Any exercises of the following type will be appropriate at this part:
    3/7 + 7/3 = ? and 5/6 + 7/15=?
    I think these four tests will be enough. All of them are for logical skills, unlike the tests created under Bologna Process.
    Dear colleagues, professors and teachers,
    You can offer these tasks to the students at your colleges and universities and share the results here, at the Research Gate platform, so that we all can see the landscape of the wretchedness and misery resulted from neoliberal economics and globalization.
    George Stoica

    There are universities with special agendas, very well hidden, and that makes it close to impossible to identify the real quality of their programs. There are universities with constantly very good results, and those should be analyzed and followed. 

  • Khaled Saad added an answer:
    10
    Are there commonly known examples of plagiarism supporting physicists in the past?
    There are probably examples of students caught engaging in scientific misconduct (e.g. not acknowledging the idea and year-long unpaid work of another scientist, or stealing confidential results). However, it is understandable that a university would do everything they can to protect a plagiarism supporting laboratory head - and continue refusing to acknowledge the life's work of the victimized scientist. Are there any examples of how to succeed scientifically against a stealing institute or university?
    Khaled Saad

    you can read this good article:

    Syed Wali Peeran, Aisha Mojtaba Ahmed, Marei Hamed Mugrabi, and Syed Ali Peeran. Simple steps to avoid plagiarism and improve scientific writing. Libyan J Med. 2013; 8: 10.3402/ljm.v8i0.21825.
    Published online 2013 Jul 25. doi: 10.3402/ljm.v8i0.21825
    PMCID: PMC3724953

  • Dashty Akrawy added an answer:
    10
    What is the physical difference between between radiation decay mode, radiation type and radiation intensity and the physical relation between them?

    I have extracted the decay data from bnl, but I am not getting the exact difference between radiation decay mode, radiation type and radiation intensity and the physical relation between them.

    Can anyone can one help me please?

    Dashty Akrawy

    The radioactive decay products we will discuss here are alpha, beta, and gamma, ordered by their ability to penetrate matter. Alpha denotes the largest particle, and it penetrates the least.
    Alpha particles carry a positive charge, beta particles carry a negative charge, and gamma rays are neutral.
    An alpha particle is made up of two protons and two neutrons bound together.
    Beta particles are high energy electrons.
    Gamma rays are waves of electromagnetic energy, or photons.

    Radioactivity
    Radioactive decay occurs when an unstable atomic nucleus loses energy by emitting energy in the form of particles or electromagnetic waves,called radiation. Isotopes are atoms of the same element (thereby having the same number of protons) which differ in the number of neutrons in their nucleus. Some isotopes of a given element are more unstable than others, causing a nuclear reaction which releases energy to achieve a more stable nuclear configuration. Such isotopes are radioactive, and are referred to as "radioisotopes."

    Types of Decay
    There are many types of emmitted particles and radiation that radioisotopes produce when they decay such as (Alpha decay Proton emission Neutron emission

    Spontaneous fission ) The types we will discuss here are: alpha, beta, and gamma (listed in increasing ability to penetrate matter). Alpha decay is seen only in heavier elements greater than atomic number 52, tellurium. The other two types of decay are seen in all of the elements. 

  • Jia Liu added an answer:
    3
    How we can generate attosecond laser pulses by using femtosecond laser pulses?

    is it possible to generate attosecond pulses by using femtosecond set-up ? can you give me an experimental idea about this technique ? 

    Jia Liu

    HHG generation, you need CEP stablized few cycle pulse, Eric gave a great answer

  • Govindasamy Usha added an answer:
    17
    Is there any relation between formula unit (Z) and lattice parameters?

    I want to know more about Formula unit (Z) in crystallography.

    Looking for clear explanation.

    Govindasamy Usha

    Dear Aditi, in general we could derive the space group ,hence the number of molecules in the asymmetric unit from the relation between the lattice parameters, When space group changes, Z will also changes.

  • R. Prosser added an answer:
    8
    How can I show that we can't reach 0 kelvin?

    We can use the associated scalar quantity 1 / T to show that we can't reach 0 Kelvin. Now, I wonder how the later is associated with T?

    R. Prosser

    There's a quick, non-rigorous (and classical thermo) answer: thermal efficiency of a heat engine is 1-(T_c/T_H); if T_c goes to 0K, then thermal efficieny goes to 1 and the engine violates the Kelvin-Planck statement of the second law. Hence 0K is unachievable.

  • Babu Balraj added an answer:
    14
    Is the second harmonic generation possible in centrosymmetric crystals?
    Second harmonic generation is possible in centrosymmetric crystals?
    Babu Balraj

    Thank you very much to all

  • Ulf Hinze added an answer:
    6
    Why we need to generate femto and attosecond laser pulses (as we have nano and microsecond order pulses) ?

    what are their (femto, pico second pulses ) advantages over nano pulses.

    Ulf Hinze

    This depends on your application. E.g. in material processing fs-laser ablation has significant advantages. See publication below.

  • Leonard A Smith added an answer:
    11
    What is the physical difference between high dimensional and low dimensional chaos?

    For glow dischage plasma system period doubling bifurcation are demonstated as a route to low dimensional chaos. Why it is low dimensional ? can anyone plz explain the physical difference between low dimensional and high dimensional chaos. From the two chaotic time series how can i distinguish them? Will i consider lyapunov exponent value?

  • Dr K.C. Bhamu added an answer:
    26
    Birefringent materials vs anisotropic materials
    What is the basic difference in birefringent material and anisotropic materials? I cant grasp the idea that what materials are simply anisotropic and what materials are classified as birefringent material.
  • Darek Michalski added an answer:
    2
    How can I measure the explosive properties of a molecule computationally?
    Explosive properties are a very important parameter in designing new explosives and propellants.
    Darek Michalski

    e.g.
    Journal of Physical Chemistry B (2007), 111(13), 3430-3437.
    Journal of Chemical Physics (2006), 124(2), 024712/1-024712/11.
    Journal of the American Chemical Society (2004), 126(45), 14997
    Journal of Chemical Physics (2002), 117(4), 1775-1785.
    doi: 10.1142/9789812811882_0011

  • Mauro Andrea Bettiati added an answer:
    2
    How does the band filling effect work?

    How does the band filling effect work when current varies?

    Kindly give a physical image of this effect.

  • Bin Jiang added an answer:
    14
    Equilibrium and self-organization.
    Is it legitimate to consider that a given system at equilibrium is self-organized?
    Bin Jiang

    @David G Grier · 60.25 · 852.41 · New York University
    Actually, it's the other way around. Nonequilibrium processes are responsible for self-organization. Systems in thermodynamic equilibrium, by contrast, have no way to change their internal organization.

    To provide an example, street networks or streets are self-organized in nature, although they are built by human beings:

    Jiang B., Zhao S., and Yin J. (2008), Self-organized natural roads for predicting traffic flow: a sensitivity study, Journal of Statistical Mechanics: Theory and Experiment, July, P07008, Preprint: http://arxiv.org/abs/0804.1630

    In the same vein, cities are self-organized as well:

    Jiang B. (2015a), Head/tail breaks for visualization of city structure and dynamics, Cities, 43, 69-77.

    + 1 more attachment

  • Bertrand Wong added an answer:
    46
    Is it possible to detect tachyons?
    We need light to bring images to our eyes when seeing or detecting. Should a particle, e.g., the theoretical tachyon, move at a velocity greater than that of light whereby light cannot catch up with it, how can this faster-than-light particle be detected? If such a faster-than-light particle does exist, which contradicts the most important tenet of SR, viz., nothing can exceed the velocity of light, we may never be able to detect it. Is there a solution?
    Bertrand Wong

    The difficulty of detecting tachyons could be due to reasons mentioned earlier. Perhaps quantum entanglement which had also stumped Einstein is a manifestation of presence of tachyons which is yet to be proved.

  • Mohamed El Naschie added an answer:
    3
    Can you suggest a good book on Polyakov loop in quark model?

    high energy physics + particles physics +applied Mathematics

  • Parviz Parvin added an answer:
    54
    According to Rayleigh scattering the sky color may be violet while it looks like blue. What is the reason for this spectral shift?
    Rayleigh scattering explains the elastic scattering of light during the interaction with gases which is proportinal to the inverse quartet of the incident wavelength.
    Parviz Parvin

    I have not found a perfect answer to my question:

    Why is not sky violet?

  • Matthew T Mayer added an answer:
    4
    Does anyone know the theoretical solar limiting, solar to hydrogen conversion efficiency of p-Si?

    For a photo-active materials which has band gab of ~1.6 eV can exhibit, theoretical calculation, solar to hydrogen conversion efficiency about 30%. What about silicon (1.1 eV )?     

    Matthew T Mayer

    (Conversion efficiency) = (power out) / (power in), where (power in) is the solar flux (100 mW/cm2 is typically used). (Power out) for water splitting can be calculated by 1.23 V * (current density in mA/cm2). Therefore, you just need to determine the maximum photocurrent density possible for your material, which involves integrating the photon flux of the solar spectrum across your bandgap-dependent absorption range (so up to 1127 nm for bandgap 1.1 eV). 

    But a material with bandgap 1.1 eV can never generate enough voltage to drive water splitting. So your current toward water splitting would be zero, and thus solar-to-hydrogen would be zero!

    + 1 more attachment

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