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D. Ya. Tsvankin V. S. Papkov V. P. Zhukov Yu. K. Godovsky V. S. Svistunov A. A. Zhdanov 《Journal of polymer science. Part A, Polymer chemistry》1985,23(4):1043-1056
The structure changes accompanying phase transitions in poly(diethylsiloxane) (PDES) have been studied by WAXS and SAXS techniques using oriented and isotropic samples. PDES may exist in two low-temperature modifications (the monoclinic α1-form and presumably the “tetragonal” β1-form) and two high-temperature modifications (the monoclinic α2-form and the “tetragonal” β2-form). In linear PDES the crystal - crystal transitions α1–α2 and β1–β2 occur near 214 and 206 K, respectively. At higher temperatures α2 (280 K) and β2 (290 K) forms transform into the mesomorphic phase αm that gradually melts at 280–300 K giving an amorphous phase. According to x-ray and density data, αm phase is also characterized by monoclinic structure slightly different from hexagonal packing. 相似文献
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Conservation of the total isotopic spin S of a two-component Bose gas-such as 87Rb-has a dramatic impact on the structure of the ground state. In the case when S is much smaller than the total number of particles N, the condensation of each of the two components occurs into at least two single-particle modes. The quantum wave function of such a ground state is a quantum superposition of the phase separated classical condensates, the most "probable" state in the superposition corresponding to the classical ground state in the sector of given N and S. 相似文献
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Depending on the Hamiltonian parameters, two-component bosons in an optical lattice can form at least three different superfluid phases in which both components participate in the superflow: a (strongly interacting) mixture of two miscible superfluids (2SF), a paired superfluid (PSF) vacuum, and (at a commensurate total filling factor) the super-counter-fluid (SCF) state. We study the universal properties of the 2SF-PSF and 2SF-SCF quantum phase transitions and show that (i) they can be mapped onto each other and (ii) their universality class is identical to the (d+1)-dimensional normal-superfluid transition in a single-component liquid. The finite-temperature 2SF-PSF(SCF) transitions and the topological properties of 2SF-PSF(SCF) interfaces are also discussed. 相似文献
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Spectroscopic studies of the silver-optimum-doped Bi2223 contacts show that the temperature dependence of the parameter Δ follows the BCS curve. However, the tunnel measurements performed for the same series of specimens did not reveal any temperature dependence of the energy gap Δ. The feature observed in the tunnel density of states was retained at temperatures T>T c , manifesting the presence of the temperature-independent pseudogap E p . The difference between the data obtained with tunnel spectroscopy and Andreev reflection spectroscopy is explained by the fact that the latter measures the true superconducting energy gap Δs(T), whereas the peaks of the tunneling conductivity are related to the total energy gap Δ of cuprates, which includes both the parameter Δs and the pseudogap $E_p :\Delta \approx \sqrt {\Delta _s^2 + E_p^2 } $ . 相似文献
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With a high-performance Monte Carlo algorithm we study the interaction-induced shift of the critical point in weakly interacting three-dimensional /psi/(4) theory (which includes quantum Bose gas). In terms of critical density, n(c), mass, m, interaction, U, and temperature, T, this shift is universal: Deltan(c)(T) = -Cm(3)T(2)U, the constant C found to be equal to 0.0140+/-0.0005. For quantum Bose gas with the scattering length a this implies DeltaT(c)/T(c) = C(0)an(1/3), with C(0) = 1.29+/-0.05. 相似文献
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V. S. Papkov V. S. Svistunov Yu. K. Godovsky A. A. Zhdanov 《Journal of Polymer Science.Polymer Physics》1987,25(9):1859-1884
Optical and calorimetric studies of the kinetics of mesophase formation and crystallization in poly(diethylsiloxane) have been conducted. The mesomorphic phase is found to grow from the isotropic melt in the form of lamellar domains about 2 μm thick in the temperature range 293–307 K. According to birefringence data, macromolecules in the mesomorphic lamellae are perpendicular to the end faces. The kinetics of mesophase formation obey the Avrami equation with the morphological parameter n close to 2 (it is equal to 1.75 ± 0.05), which corresponds to the two-dimensional growth of the mesomorphic phase from athermal nuclei. The limiting conversion of the isotropic melt was shown to be temperature-dependent. This is likely to be connected with a change in the number of nuclei with temperature. The crystallization of polymer from the mesomorphic state occurs with retention of the optical texture of the sample. The process proceeds not as a sporadic crystallization of individual mesomorphic lamellae but as a growth of the nucleated crystalline regions via a consecutive incorporation of adjacent crystallizing lamellae. 相似文献
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