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Phase Transitions - Science topic
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Questions related to Phase Transitions
Paradox 1 - The Laws of Physics Invalidate Themselves, When They Enter the Singularity Controlled by Themselves.
Paradox 2 - The Collapse of Matter Caused by the Law of Gravity Will Eventually Destroy the Law of Gravity.
The laws of physics dominate the structure and behavior of matter. Different levels of material structure correspond to different laws of physics. According to reductionism, when we require the structure of matter to be reduced, the corresponding laws of physics are also reduced. Different levels of physical laws correspond to different physical equations, many of which have singularities. Higher level equations may enter singularities when forced by strong external conditions, pressure, temperature, etc., resulting in phase transitions such as lattice and magnetic properties being destroyed. Essentially the higher level physics equations have failed and entered the lower level physics equations. Obviously there should exist a lowest level physics equation which cannot be reduced further, it would be the last line of defense after all the higher level equations have failed and it is not allowed to enter the singularity. This equation is the ultimate equation. The equation corresponding to the Hawking-Penrose spacetime singularity [1] should be such an equation.
We can think of the physical equations as a description of a dynamical system because they are all direct or indirect expressions of energy-momentum quantities, and we have no evidence that it is possible to completely detach any physical parameter, macroscopic or microscopic, from the Lagrangian and Hamiltonian.
Gravitational collapse causes black holes, which have singularities [2]. What characterizes a singularity? Any finite parameter before entering a spacetime singularity becomes infinite after entering the singularity. Information becomes infinite, energy-momentum becomes infinite, but all material properties disappears completely. A dynamical equation, transitioning from finite to infinite, is impossible because there is no infinite source of dynamics, and also the Uncertainty Principle would prevent this singularity from being achieved*. Therefore, while there must be a singularity according to the Singularity Principle, this singularity must be inaccessible, or will not enter. Before entering this singularity, a sufficiently long period of time must have elapsed, waiting for the conditions that would destroy it, such as the collision of two black holes.
Most of these singularities, however, can usually be resolved by pointing out that the equations are missing some factor, or noting the physical impossibility of ever reaching the singularity point. In other words, they are probably not 'real'.” [3] We believe this statement is correct. Nature will not destroy by itself the causality it has established.
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Notes
* According to the uncertainty principle, finite energy and momentum cannot be concentrated at a single point in space-time.
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References
[1] Hawking, S. (1966). "Singularities and the geometry of spacetime." The European Physical Journal H 39(4): 413-503.
[2] Hawking, S. W. and R. Penrose (1970). "The singularities of gravitational collapse and cosmology." Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences 314(1519): 529-548.
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补充 2023-1-14
Structural Logic Paradox
Russell once wrote a letter to Ludwig Wittgenstein while visiting China (1920 - 1921) in which he said "I am living in a Chinese house built around a courtyard *......" [1]. The phrase would probably mean to the West, "I live in a house built around the back of a yard." Russell was a logician, but there is clearly a logical problem with this expression, since the yard is determined by the house built, not vice versa. The same expression is reflected in a very famous poem "A Moonlit Night On The Spring River" from the Tang Dynasty (618BC - 907BC) in China. One of the lines is: "We do not know tonight for whom she sheds her ray, But hear the river say to its water adieu." The problem here is that the river exists because of the water, and without the water there would be no river. Therefore, there would be no logic of the river saying goodbye to its water. There are, I believe, many more examples of this kind, and perhaps we can reduce these problems to a structural logic pradox †.
Ignoring the above logical problems will not have any effect on literature, but it should become a serious issue in physics. The biggest obstacle in current physics is that we do not know the structure of elementary particles and black holes. Renormalization is an effective technique, but offers an alternative result that masks the internal structure and can only be considered a stopgap tool. Hawking and Penrose proved the Singularity Theorem, but no clear view has been developed on how to treat singularities. It seems to us that this scenario is the same problem as the structural logic described above. Without black holes (and perhaps elementary particles) there would be no singularities, and (virtual) singularities accompany black holes. Since there is a black hole and there is a singularity, how does a black hole not collapse today because of a singularity, will collapse tomorrow because of the same singularity? Do yards make houses disappear? Does a river make water disappear? This is the realistic explanation of the "paradox" in the subtitle of this question. The laws of physics do not destroy themselves.
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Notes
* One of the typical architectural patterns in Beijing, China, is the "quadrangle", which is usually a square open space with houses built along the perimeter, and when the houses are built, a courtyard is formed in the center. Thus, before the houses were built, it was the field, not the courtyard. The yard must have been formed after the house was built, even though that center open space did not substantially change before or after the building, but the concept changed.
† I hope some logician or philosopher will point out the impropriety.
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References
[1] Monk, R. (1990). Ludwig Wittgenstein: the duty of genius. London: J. Cape. Morgan, G. (Chinese version @2011)
Anybody is having solution to problems of Statistical Mechanics of Phase Transitions by J. M. Yeomans?
The normal Pourbaix-Diagram only shows the corrosivity (immunity/corrosion/passivity) by 25°C. I am interested in how this varies depending on temperature. As an example Fe is not corrosive in the range of 9.5 to 12.5 pH by 25°C. How changes this depending on temperature? By which temperature closes this “window of no corrosion”? Up to which temperature can I reduce corrosion be choosing the right pH value?
Hi all,
I am looking for references about measuring crystallisation and metling enthalpy of pure water with differential scanning calorimetry (DSC).
Although this seems to be quite a straightforward job, are there any challenges associated with it?
Moreover, how can the presence of ions/proteins/biological membrane fragments, dissolved in water, affect the enthalpy of those phase transitions?
With many thanks
Best
Filippo
Hello!. It has been experimentally proven that when about 3-3.4 mol.% Y2O3 is doped into the structure of monoclinic ZrO2, this material (m-ZrO2) is partially stabilized and passes into the tetragonal phase (m-t phase transitions of ZrO2 ) and with a further increase in the Y2O3 concentration to 8 mol. % the system is completely stabilized and goes into a cubic one.
However, we want to prove this using DFT calculations, but we cannot do this because some of our results do not match the experiment (relaxed volume and lattice parameters are very different). Please tell me how to set up the calculation parameters in the VASP package (how to set up the parameters of the poscar and contcar files) so that we get the correct results and correctly simulate the phase transitions of zirconia (m-t and t-c or m-c phase transitions in the case of doping with 8 mol.% Y2O3)?.
I want to calculate the Gibbs free energy and phase transitions for my high entropy alloy. I saw that the CALPHAD program is used more. How can I do this calculation? what type of file do I need as the input file. I have never used this program and these calculations. I would be happy if you could help me.
I want to know if the number of fringes and their shape is an important factor for the accuracy of phase definition?
Dear Fellows I checked very recent literature for the P-T phase diagram by means of exp. measurements on Metallic Hydrogen.
I found several interesting papers that show its metallic phase at high pressure: Any comments please? are there any new DFT calculations for a Metallic Hydrogen P-T Phase Diagram?
1. Metallic hydrogen F Silvera et al 2018 J. Phys.: Condens. Matter in press https://doi.org/10.1088/1361-648X/aac401
Figures 6 and 8
2. Insulator-metal transition in liquid hydrogen and deuterium
Shuqing Jiang, Nicholas Holtgrewe, Zachary M. Geballe, Sergey S. Lobanov, Mohammad F. Mahmood, R. Stewart McWilliams, Alexander F. Goncharov arXiv:1810.01360v1
Fig. 5
3. Theory of high pressure hydrogen, made simple Ioan B Magd˘au, Floris Balm and Graeme J Ackland
IOP Conf. Series: Journal of Physics: Conf. Series 950 (2017) 042059 doi :10.1088/1742-6596/950/4/042059
Fig. 1
4. Observation of the Wigner-Huntington transition to metallic hydrogen Ranga P. Dias, Isaac F. Silvera
Science 17 Feb 2017:
Vol. 355, Issue 6326, pp. 715-718
DOI: 10.1126/science.aal1579
Fig 1
Dear all,
Please, any suggested publications to read about any real applications were performed using Bragg-edge neutron imaging BUT with "thermal" neutron beam (1.8 A° +/-), if existed, other than the most famous ones that use cold monochromatic beams for strain mapping or magnetism studies?
Thanks a lot in advance.
Mahmoud
Potts model is one of the earliest models which continues to receive attention. In a q-state Potts model the spin at any site can take any one of the q different states (1,2, …, q). If the spins at two different sites are the same then the corresponding energy is –J and otherwise it is zero. The spins reside on 2D or 3D square lattice. The magnetization (M) is the order parameter. The magnetization is defined as follows: if N1 is the number of spins in state 1, N2 is the number of spins in state 2 and similarly for all other states and Nmax is maximum among N1, N2, N3, … , Nq, then M=[q(Nmax/N)-1]/(q-1).
Hi,
Does the bend in absorption curve of a semiconductor thin films depicts the presence of both direct and indirect phase transition?
Thankyou
Any type of system: physical, chemical, biological, social, etc.
Classification of thermodynamic phase transitions relies on the analiticity of the Helmholtz free energy (or the corresponding thermodynamic potential, depending on the ensemble). As it is widely known, first-order phase transitions are characterized by a discontinuity in the first derivative of the thermodynamic potential with respect to the relevant intensive variable, while in continuous phase transitions the thermodynamic potentials are continuous and differentiable, but high-order derivatives may be undefined.
Imagine now that one considers a system udergoing a phase transition for given values of temperature, pressure, etc. Is it possible to infer that such a system will exhibit a thermodynamic phase transition by looking at the microcanonical density of states (DOS), instead of the thermodynamic potentials? Does the DOS carry some signature of the phase transitions? If yes, what traits indicate the order of the transition ?
By studying some classical papers (like those on random energy models and trap models by Derrida), one can infer, for instance, that a DOS with edge states can be linked to a thermodynamic freezing (glass) transition. Are there similar signs in the simpler cases of first and second order phase transitions? I intuitively believe there must be, since, for instance, the canonical partition function is simply the Laplace transform of the microcanonical DOS. But I don't know what those signs may be.
A phase transition of order k is mathematically characterized by a loss of regularity of free energy f: f is k-1 differentiable but not k differentiable. There are many examples of first and second order phase transitions in experiments and in models. There are also cases where f is C^{\infty} but not analytic (Griffith singularities).
But are their known example of phase transition of order k, k>2 ?
A third order phase transition would mean that quantities like susceptibility or heat capacity are not differentiable with respect to parameters variations. But I have no idea of what this means physically.
The Mermin-Wagner theorem implies for the standard classical Heisenberg model in two spatial dimensions that there cannot be spontaneous symmetry breaking. At the same time, there is a body of evidence, often also from the 60ies, that the system is undergoing a phase transition at finite temperatures. How is this compatible? Is it that this is a Kosterlitz-Thoughless type phase transition? Where is the catch?
Thermal hysteresis in liquid solid can be defined by undercooling. I am looking into thermal hysteresis in gas liquid phase transition.. is that possible? I cant seem to find any literature on this
I'm trying to solve the problems for statistical mechanics.
Is there any solution manual for "lectures on phase transition and the renormalization group" by Nigel Goldenfeld ?
Greetings everyone, hope you are all doing well. I just want a clear definition about how we can analyze the structural morphology of RE doped phosphors with powder XRD and what are all the significant changes that we can observe from the XRD data of the material as the concentration of RE varies, like structural phase transitions.
Stay healthy and Thank you
Ferromagnetic ordering breaks the time-reversal invariance irrespective of nature and type of ferromagnetic ordering. Does anti-ferromagnetic ordering also breaks the time-reversal invariance irrespective of nature and type or one can observed breaking of time-reversal symmetries in some AFM state (Like Neel State) and its preservation on other states?
In AFM state, is staggered magnetization only responsible for time revers symmetry breaking or any other intrinsic effect can also lead to time revers symmetry breaking?
In the ferromagnetic state, where the magnetic moments have spontaneously chosen to point in one particular direction, time reversal effect inverts the magnetization, so it would have a microscopically-observable effect. We thus say that ferromagnetism breaks time-reversal symmetry. What about AFM (M =0), is time-reversal symmetry broken in all case just because of change of sign of their staggered magnetization due to time reversal effect or time-revers symmetry breaking will depend upon type and nature of AFM state.
ABO3 perovskites show cubic structure at high temperatures where the
A-site cation is having 12 coordination with oxygen ions and
B-site cation is having 6 coordination with oxygen ions
But whereas in low temperature stable phase of ABO3 structures (particularly in rhombohedral sodium bismuth titanate)
What is the effective A-site cation coordination (6 or 9 or any other) in NBT?
Please give me brief answer with references.
Dear all, I have calculated phonon frequency for perovskite compound at cubic phase. As it is known a presence of soft modes at this structure give new structure more stable than a cubic phase. But in my calculations I found these new structures less stable than parent structure (cubic) with little difference about 2 meV. So in this case, my calculation is wrong or it is correct and just it has no phase transition to these structures. Any help please?
I am pleased to invite you to submit your manuscript(s) to MDPI, Applied Sciences, for the Special Issue “Phase Transitions in Polymers and Polymer-Based (Nano)Composites” Additional details are available at https://www.mdpi.com/journal/applsci/special_issues/phase_transitions_polymer
The IV-VI narrow band gap semiconductor GeTe undergoes a ferroelectric phase transition at about 600 K. At this transition the high temperature paraelectric cubic NaCl type phase undergoes a structural phase transition to the rhombohedral ferroelectric phase. In the high temperature phase all Ge-Te distances of the GeTe6 octahedra are equal whereas in the low temperature phase there exist two sets of Ge-Te distances: short and long. The phase transition was previously assumed to be a displacive type phase transition in which the short and long Ge-Te bond distances of the rhomboheral phase gradually approach each other with increasing temperature and become equal in the cubic phase. Recent EXAFS and PDF investigation of total scattering X-ray data suggest that the phase transition is order-disorder type. According to these investigations nothing at all happens to the short and long bond distances, they remain unequal in both phases in the local scale. Please note that the above two techniques probe the local structure. The phase transition does not occur at all in the local scale or the short-sighted local probe is in fact totally bind to probe the phase transition. The soft mode of the phase transition enters into the energy windows of the local probes and the local probe records soft mode dynamics as a static snap-shot because it does not analyze the energy. Can we then trust this local probe picture?
ABO3 compounds are stabilize in high symmetry cubic phase at high temperatures. As the temperature is lowered, it undergoes distortion and shows low symmetry phases like orthorombic or/and rhombohedral ?
What is the actual reason or theory behind this ???
Thanks in advance.
The generic concept that I am suggesting may be behind the observation of higher symmetry at high temperature is captured in the attached schematic. Suppose that distorting the high symmetry structure in either the positive or negative direction along some coordinate leads to a lower symmetry structure of lower energy. Effectively this produces a symmetric double well potential energy curve. At low temperature the system can get trapped in one of the potential wells and exhibit a low symmetry structure. (This is certainly true at least locally, i.e. for one or a few adjacent unit cells. It is also possible that once a given cell "freezes out" an entire adjacent domain will distort and freeze out the in the same direction because that minimizes the energy.) At sufficiently high temperature the system will have sufficient thermal energy to overcome the potential barrier so the observed structure is an average of the two symmetry-related low symmetry structure, and will exhibit the symmetry of the zero distortion point. Related ideas are elaborated on in the reference that Robert Wexler cites.
I am pleased to announce that the Journal: Applied Sciences will publish a special issue focused on “Phase Transitions in Polymers and Polymer-Based (Nano)Composites”.
I use this occasion to invite you to submit your relevant contributions.
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- As we know that TWs formation takes place due to cubic to low symmetry structural phase transition ( due to either by cation displacement or octahedra rotation or both), which minimize the total strain of low symmetry phase. If i consider, phase transition only due to octahedra rotation or tilting, how the TWs will form in this type of structure ? i want to visualize Tws formation by rotating the octahedra of unit cell (which is responsible for structural phase transition as well)?
I am having 4 inorganic salts - NaOH KOH NaNO3 KNO3. I want to prepare a salt mixture using any of these 4 salts which should have melting point in the range 175-215 °C.
Here number of cycles means, phase transition from amorphous state to crystalline state and vice-versa. Also discuss the method by which it can be measured. is it experimentally or theoretically determined?
If yes, than what is the effect on the expansion of 3YSZ substrate. Since the lattice parameter in these two phase are different so there must be an expansion or contraction in the sample. How much TEC changes because of the appearance of the new monoclinic phase. Please suggest me any research paper if it addressed to such kind of issue. Thank you
I am planning to use hydrate salt as a phase change material then what kind of material i have to select for the container in which PCM can be kept?
A. Einstein in 1920 realized that his theory might not be complete, in the sense that Mach's principle was not consistently applied to the general relativity theory as space-time is not made of matter-energy, see: http://www-history.mcs.st-andrews.ac.uk/Extras/Einstein_ether.html . He mentioned the idea of a relativistic aether, not the static one, a more relativistic one. I have no empirical argument to prove what I say so far, but I say it anyway, for the sake of discussion. In one of my recent paper: , I explore the hypothesis stating that space-time was a material with some elastic properties. My conclusion is that the stiffness of space-time is so high at the present epoch (in the cosmological scale) that we cannot really interact with it, except through the classical general relativistic geometrical-like interaction. However, following this hypothesis, one could find best-fit parameters that predict cosmological inflation and resolve the so-called cosmological constant problem. In this regime, space-time is elastic, and can be deformed as any other material, as any other field that can be quantized. Why space-time should be 'so' different than any other field and in the same time be quantized ? Why not considering that space-time was as any other field, and experienced a phase transition that made him stiffed ? May be geometry is a a consequence of that, and not the cause. Then, the Mach principle becomes consistent to the theory, and the space-time background hypothesis is not required anymore.
I want a least mathematical explanation about why there is no long range order in 2D. I have already read the papers of Mermin, Wagner, Hohenburg etc. But I am afraid they are too mathematical for me. I could not understand at what point 2D becomes different than 3D in these calculations.
FYI ...
Dear All,
Fano interference is usually observed between the zone-folded transverse acoustic (FTA) phonon modes and the electronic continuum in n-type 4H-SiC. In our n-type 4H-SiC samples, the FTA (-) and FTA(+) modes are noticed at 197.4 cm-1 and 205.7 cm-1 respectively (at room temperature).
I'm trying to fit the these modes according to reference Mitani et. al. JAP 2012. But quite unsuccessful in fitting these modes.
1. Before fitting both FTA (-) and FTA(+) modes in a single fitting function, I first tried by fitting FTA(+) mode separately. (I subtracted background to a minimum then performed fitting), but did not succeed.
2. I have also normalized to unity after background subtraction, but again not succeeded.
3. I initialized the parameters as per the reference plots given in Mitani et. al. 2012. It did not work out.
4. I would be grateful if someone could find the mistake that I'm doing in the fitting methodology. I am also attaching the raw excel data file for your reference. Someone please try fitting the given data.
5. Also, in literature, I'm unable to find the fitting parameters for a 4H-SiC sample with specific dopant/carrier concentration.
Why Carbon filament is elastic at room temperature and becomes plastic when heated by current? How to understand the phase transition from crystalline to amorphous ?
is there anyone who know the temperature of phase transitions of FAPbI3 perovskite?
Dear all,
Recently, I have found that a simple cubic crystal show structural instability under high pressure (above 50 GPa), that is negative phonon frequency. I have checked changing parameter and also in QE, VASP-phonopy, but results were same. The negative frequencies are also high ~200cm-1 along Gamma-Gamma. The ground state space group is #215. Does it mean the space group has changed? I think that it should not change cubic structure since we press it in all side and thus it should be compressed. what is the possible reason? I know that fcc-bcc transition possible but sc? If so, then what may be the possible structure? Thank you advances!
Dear All,
I have attached powder XRD pattern at 0 GPa and 100 GPa, can you gauge any phase transition from this?
I am sure, this is likely different from case to case, but I am wondering if in general one would expect a larger change in entropy during a first order phase transition than for a second order one.
I have been reading a bit about supercooling and glass formation and some questions came to my mind.
In the landau picture of a phase transition supercooling/superheating emerges as a local minima separated from the global minima by an energy barrier. With a decrease/increase the energy barrier eventually vanishes at T*/T** and the system transforms into the groundstate.
Glasses are described as states where time is essentally held still, meaning that kinetics are arrested. However it does not need to be in a local minima.
1. Am I correct that, assuming there is no glass transition, if I wait long enough the supercooled state transforms into the ground state and this time decreases the closer I get to T*?
2. Is it possible to distinguish glassy states from supercooled metastable states using relaxation measurements? E.g. from the temperature dependece?
3. In systems where the glass temperature Tg is well below T* do I observe a glass to crystal transition on heating?
Good day everyone. I am reviewing a paper on "Complete Analysis of Phase Transitions and Ensemble Equivalence for the
Curie-Weiss-Potts Model by Richard Ellis". Please can someone kindly assist me on how they got the critical inverse temperature and s(critical inverse temperature) .Thank you
Hello all,
I am trying to simulate spinoidal decomposition using phase-field method. Most of the literature I could have given equations in dimensionless form. However, I intend to solve them in dimensional form.
Can someone suggest some reference where this problem has been dealt in dimensional form.
It will be really helpful.
Thanks
Deewakar
Hello
I would like to know how the temperatures of tetragonal to orthorhombic and orthorhombic to rhombohedral transitions could be determined in (Ba,Sr,Ca)TiO3 perovskites based on the temperature dependence of permittivity data.
I doing LCR measurements on (Ba,Sr,Ca)TiO3. In addition to the cubic to tetragonal transition manifested by a clear peak on the dielectric permittivity vs temperature graph at Curie temperature, additional transitions (tetragonal to orthorhombic and orthorhombic to rhombohedral) are also present. Unfortunately they do not show clear peaks as at Tc and often look like some humps on the dielectric permittivity curve. All 3 transitions correspond with a clear sharp peaks (at 100 Hz) on the temperature dependence of loss factor (tan(D)). However those tan(D) peaks shifted by about 10 K to lower temperatures (based on the clear position of Tc).
Even though those low temperature transitions are discussed in the literature, I failed to find description of their estimations.
Thank you in advance.
Andrey
How to mix a low pressure Liquid (say 10 bar) with a 40-80 micron powders in a mixing chamber?
My sample is made by sps with two raw materials. I got two pellets,and the sps process is like 0~900℃ (9mins/18mins);900-980(4mins/8mins)980-1000(2mins/4mins)
1000(5mins/10mins).after that,i got the good looking pellets from die,polished the surface.
in order to keep them(2 pellets) homogeneous, i put them into sintering at 1200℃for 1h(heating rate is 5℃/min).Then ,one is broken when the other is ok.
I don't know why,and it happened before.sometimes it works,sometimes it break.
Do i need to do a SEM?
Besides i checked the XRD pattern ,there is no phase transition.
I am mainly concerned about the analytic continuability of the partition function across the phase boundaries of different orders.
Critical slowing down at bifurcations is a consequence of the vanishing (real part) of eigenvalues. Phase transitions show critical slowing down as a collective phenomenon and consequence of exactly what (diverging correlation length?)?
Hi,
I apologize for this apparently silly question, but please, could you point me out if there is an underlying relationship between the defect driven phase transition and the directed percolation?
Secondly, is it possible to have a system which undergoes a KT transition at T1 generating free vortices, and subsequent by a spatial spreading of disorder via directed percolation at T2?
Please, if there is any relevant examples and materials, do let me know.
Many thanks.
Wang Zhe
How the different multilayer thickness of the AlN/GaN superlattice on the the sapphire substrate will affect the A1(LO) mode in the Raman spectra.
How it will differs from thinner layers ( few nm) to thicker ones ( few hundreds of nm)
If the layer thickness of superlattice affects A1(LO) mode ( it can couple with charge carriers in the lattice), then what may be the probable reason for it...? is there any relation with the carrier concentration?
I've researched the consequences of discovering the ferroelectric phase transition in ice crystallised in liquid nitrogen as a Cambridge undergraduate in 1967, see attached. You'll need to 'think outside the box' to understand them. They solve many questions, first learn the biological roles of 'transport DNA', 'minions' and resonance.Solving my problems might persuade you that basic things are simple. Yours truly, Michael Thomas Deans, MA Cantab MSc Lond, www.scienceuncoiled.co.uk, michaeltdeans@gmail.com.
As you know, PLGA-PEG-PLGA is a thermosensitive polymer with a sol-gel phase transition feature at physiological temperature. Does anyone know the typical viscosity of this tri-block copolymer at 37C?
Its G' and G'' are 100 and 85 (Pa), respectively, yet no information on its viscosity. Is there any model to calculate viscosity based on those?
If At the Bigbang there was one single fundamental interaction could successive phase transitions explain the existence of four interactions today? Then could dark energy be another phase transition as the universe cools down?
proceddure to calculate transiton pressure from B3 to B1 phase in WN using quantum esspresso code.
Can a melted crystalline compound show a glass transition before an LC transition on a DSC? In a compound we observed a DSC trace with a large melting peak, then a drop in heat flow that could be attributed to a glass transition and then a small liquid crystal transition. This seems strange to me, as a glass should occur in a subcooled liquid, but the effect seems reproducible.
Hi!
Please, could anyone point me out an intuitive way to understand the exponential divergence of the correlation length in the KT-transition; in contrast to the usual algebraic divergence in the common sense of critical phenomena?
Thank you.
Wang Zhe
I am getting signature of semiconductor to metallic type of transition in conductivity and impedance measurements through decrease in conductivity with Temperature and increase in resistance in Bi2Fe4O9 which is p type semiconductor. I got to know this may be a feature of degenerate semiconductor. In literature I found out that this may be because of second order transition from Ferroelectric to paraelectric transition but there is no structural phase transition observed. So Can anyone please explain how would I confirm the origin of such feature?
As the title. How can I differentiate the two peaks? I tried Voigt fitting function, but the fitting is not well. I guess the heat flow is not simple Gaussian or Lorentzian distribution. I also tried to see the derivative heat flow, but I have no clue how the phase transition temperature located from that curve.
As we know, the resolution of 3DAP is anisotropic. The best resolution is reached along the needle axis direction, and could below 0.25 nm. However, the resolution along transverse direction is worse, and may around 1nm. Then, when we apply radial distribution function to analyze the atomic pairing relationship in 3DAP data, the result with 1nm is not reliable and may be wrong. I think this conclusion is true and what do you think. Is there any other reliable method to find the nano-sized cluster in a system. Thanks.
I want to know a method like electron energy loss spectroscopy (EELS) which can determine transitions (single and plasmonic) in materials. But as I know, EELS is slow and it is measuring data between 0.1 to 1 second.
I want to know a similar way but more faster, in the order on micro or nano seconds or even faster.
Thanks
Hello all,
I am studying the laminar-turbulent phase transition. It is well known that in pipe flows, turbulence first manifests itself in localized turbulent patches surrounded by laminar background. On the other that, it is noteworthy that at transitional flow regime, the Reynolds number is relatively low and the flow is known to be dominated by coherent structures of some kind. Since coherent structures can not survive in high Reynolds numbers, I suppose that coherent structures are essentially a transient phenomenon governing the transitional flow regime.
However, these two pictures for transitional flow regime:
1) turbulence start with a well-defined spot embedded in the laminar environment and grows bigger and bigger until occupying the entire flow domain; and
2) Initially, transitional flow regime is overwhelmingly dominated by coherent structures; coherence is lost as Re increases and vanishes in fully developed turbulence.
to me, are contradicting. I would like to know if there is a connection between coherent structures and turbulent patches. And how about other confusing concepts such as traveling waves and laminar streaks?
Wish all a Merry Christmas and a prosperous new year ahead!
Thank you.
Very kind wishes,
Wang Zhe
Dear Adrian and Moshe,
Thank you for sharing your works, I will read them carefully.
In the study of laminar-turbulent phase transition, I mainly consider the pipe flow and the Couette flow because they are linearly stable so that the instability must be inherent in the nonlinear inertia term. Instead of perturbing laminar base flows, I perturb the nonlinear inertia term and study their bifurcations in the phase space. In this sense, I am still working under the continuum hypothesis, I am afraid.
I found that the original laminar flow can become chaotic by undergoing the following bifurcation sequence: Counterrotating vortical dipoles (by reflectional symmetry) - periodic solutions (reflectional symmetry breaking, generation of helicity from original helicity-free flow) - 2-torus (a slow frequency is born, possibly associated with coherent structures) - homoclinic orbit breaks up - Smale horseshoe (chaos is born, turbulent spots occur).
Now I am trying to find physical evidence and interpretation for the mathematical model and associated bifurcation sequence. I was thinking about the possibility of existing a coherent state between the laminar and fully developed turbulent states. I work at the school of electrical engineering, so I actually took an analog from the phase transition between ferromagnetic and paramagnetic materials.
I am aware that the dynamical system theory studies the temporal chaos, while coherent structures and turbulent spots are spatially organized structures, but the resemblance is so seductive that I cannot resist conjecturing there exists certain unknown mechanism synchronize fluids with coherent state and chaotic state respectively into coherent structures and turbulent packets. During the transition, the coherent and turbulent states compete for their appearance, until reaching the critical Reynolds number, coherent states vanishes, and turbulence becomes self-sustaining. Such that, the "coherent structure" here may not be certain well-defined structures restricted in wall-bounded shear flows, instead, they are long-lasting periodic solutions of the Navier-Stokes equation, coexisting with turbulent spots....
Merry Christmas and happy holidays!
Best wishes from sunny Singapore,
Wang Zhe
I'd like to know if is it possible to detect an hexagonal (D024) eta phase (Ni3Ti) in a Precipitation Hardening steel using raman spectroscopy. This phase is 2% vol maximum in a martensitic steel.
If I affected on a gas with an unknown pressure and I measured the tempreture ;could I use an equation to calculate the pressure? And what is that equation?
In case of non-Brownian suspensions, how does one confirm the presence of shear banding. I am using a Couette geometry. While reading through literature I came across the mention of a "positive slope" in the yielding region of the flow curve which appears due to the curvature of the couette geometry. For parallel and cone plate geometries this region is flat or displays a negative slope. However, what I am confused about is whether that positive slope needs to have a certain "minimum" value or any change in slope qualifies as banding? How much does the slope change vis a vis the initial low shear yielding slope. Is there maybe some ratio below or above which it qualifies as shear banding?
The stress ramp flow curve shows three regions in my case. A gradually yielding region at lower shear rates, a lower slope region around yielding and again a high slope region beyond the yielding. Am I definitely seeing shear banding or are there some other confirmations that I need to address before I conclude so. Also what are any other interpretations other than shear banding, for such systems?
You mean like the figure below? If yes, see the reference there.
Hi, everyone,
My goal is to simulate the deposition of the particle in a high temperature environment, the key problem is to simulate the growth of the deposition in a wall boundary, I read a thesis named <development of a predictive cfd fouling model for diesel engine exhaust gas systems> by Paz, his method is to change a mesh cell near the wall boundary from fluid to solid when the deposition thickness reaches to the top of a cell.
But I'm struggled in finding the way to change the cell's type, does anyone is doing or have done the similar research, could you give me some advice, thanks
Kind Regards
Li Zishuo
Now i am working on a organic salt which is having Orthorhombic structure in room temperature and it exhibits a structural phase transition at 426K. I have calculated 288 Raman modes for Orthorhombic and 141 for Monoclinic structure, but when i have done temperature dependence Raman there is no change in the Raman spectrum at phase transition temperature. what are the possible reason for this?
1) An apparent prerequisite to put the question is that martensite gets rather close to bainite in tempering as the dislocation density decreases and carbides precipitate. Although the generic crystallography (selection of OR variants) often keeps the same, from the viewpoint of final practical properties the process is equivalent to the bainitic transformation…
2) The confusion has become even stronger when S. Morito et al have found a curious transformation of purely pearlite steel under cold severe deformation
(2015, doi: 10.1016/j.matpr.2015.07.430): dissolution of cementite and, hence, carbon-related tetragonality of the lattice i.e. BCC-to-BCT transition characteristic of martensite.
Very sorry for vulgarization, this materials science issue resembles the following social problem actual for some people. Allowing only for secondary sexual signs in everyday life, may one consider a trans-gender body as female (bainite), though GENETICALLY it remains male (martensite) ?
Dear all,
I am planning to investigate laminar-turbulent phase transition in fluid dynamics via studying the bifurcation characteristics of the Navier-Stokes equation. I would like to know if there is any theory which details the variation of an index at a bifurcations points during the phase transition.
Thank you.
Wang Zhe
I am studying the phase transition of metal alloy from metastable state to equilibrium state. I am wondering if I can use the DSC from metastable state to plot the Tammann diagram to determine the eutectic composition of the metastable state?
I have seen the papers in which rate constant is calculated for substituted azobenzene in various solvents. Is there any details regarding the rate constant for cis-trans isomerization of azobenenzene in gas phase (experiment or theory) ?
i read a lot of paper on diffusion in solids but didn't get any idea about specific diffusion constant?
I add water phase while organic phase is stirring with 3000 rpm but the water phase can not disperse and stick to the bottom of the beaker.
Dear All,
I have a hypothetical question which resembles my current problem. any guidance will be helpful to understand my current observations in the study.
Let's assume that:
1. I have a polymer having alternate units of 2 types of monomers, First type of monomer can easily go from state A-B while for another one A-B transition is difficult.
Now, If I want to imagine a potential of mean force for complete A-B transition of a polymer ,
1. will it be zig-zag PMF due to odd-even effect?
2. How can one prove cooperativity in such transition?
Thanks once again for reading, any help will be really appreciated.
I have seen papers where the maxima of d (lnp)/d(1/T) vs T plots is considered as Neel temperature (TN) for an antiferromagnet or in some cases, charge ordering temperature (in perovskite oxides). Is it related to the sudden change in resistivity with magnetic ordering ?If anyone can suggest some literature for this?
