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Sökning: L773:1063 777X

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1.
  • Aleksandrovskii, A. N., et al. (författare)
  • Effect of argon on the thermal expansion of fullerite C60 at helium temperatures
  • 2001
  • Ingår i: Low temperature physics (Woodbury, N.Y., Print). - American Institute of Physics. - 1063-777X. ; 27:3, s. 245-246
  • Tidskriftsartikel (refereegranskat)abstract
    • The linear thermal expansion of compacted Ar-doped fullerite C60(ArxC60) is investigated at 2–12 K using a dilatometric method. The thermal expansion of ArxC60 is also studied after partial desaturation of argon from fullerite. It is revealed that argon doping resulted in a considerable change of the temperature dependence of the thermal expansion of fullerite. An explanation of the observed effects is proposed.
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2.
  • Aleksandrovskii, A. N., et al. (författare)
  • Negative thermal expansion of fullerite C60 at helium temperatures
  • 1997
  • Ingår i: Low temperature physics (Woodbury, N.Y., Print). - 1063-777X. ; 23:11, s. 943-946
  • Tidskriftsartikel (refereegranskat)abstract
    • The thermal expansion of fullerite C60 has been measured in the temperature range 2-9 K. A compacted fullerite sample with a diameter of about 6 mm and height of 2.4 mm was used. It was found that at temperatures below ~ 3.4 K the linear thermal expansion coefficient becomes negative. At temperatures above 5 K our results are in good agreement with the available literature data. A qualitative explanation of the results is proposed.
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3.
  • Aleksandrovskii, A.N., et al. (författare)
  • On the polyamorphism of fullerite-based orientational glasses.
  • 2005
  • Ingår i: Low Temperature Physics. - 1063-777X. ; 31:5, s. 429-444
  • Tidskriftsartikel (refereegranskat)abstract
    • The dilatometric investigation in the temperature range of 2–28 K shows that a first-orderpolyamorphous transition occurs in the orientational glasses based on C60 doped with H2, D2 andXe. A polyamorphous transition was also detected in C60 doped with Kr and He. It is observed thatthe hysteresis of thermal expansion caused by the polyamorphous transition (and, hence, the transitiontemperature) is essentially dependent on the type of doping gas. Both positive and negativecontributions to the thermal expansion were observed in the low-temperature phase of the glasses.The relaxation time of the negative contribution occurs to be much longer than that of the positivecontribution. The positive contribution is found to be due to phonon and libron modes, whilst thenegative contribution is attributed to tunneling states of the C60 molecules. The characteristictime of the phase transformation from the low-T phase to the high-T phase has been found for theC60–H2 system at 12 K. A theoretical model is proposed to interpret these observed phenomena.The theoretical model proposed, includes a consideration of the nature of polyamorphism inglasses, as well as the thermodynamics and kinetics of the transition. A model of noninteractingtunneling states is used to explain the negative contribution to the thermal expansion. The experimentaldata obtained is considered within the framework of the theoretical model. From the theoreticalmodel the order of magnitude of the polyamorphous transition temperature has been estimated.It is found that the late stage of the polyamorphous transformation is described well by theKolmogorov law with an exponent of n = 1. At this stage of the transformation, the two-dimensionalphase boundary moves along the normal, and the nucleation is not important.
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4.
  • Aleksandrovskii, A.N., et al. (författare)
  • Thermal expansion of fullerite C60 alloyed with argon and neon
  • 2001
  • Ingår i: Low temperature physics (Woodbury, N.Y., Print). - Woodbury : American Institute of Physics. - 1063-777X. ; 27:12, s. 1033-1036
  • Tidskriftsartikel (refereegranskat)abstract
    • The linear thermal expansion of compacted fullerite C60 alloyed with argon (ArxC60) and neon (NexC60) are investigated by a dilatometric method. The experimental temperature is 2–12 K. In the same temperature interval the thermal expansion of ArxC60 and NexC60 are examined after partial desaturation of the gases from fullerite. It is found that Ar and Ne alloying affects the temperature dependence of the thermal expansion coefficient of C60 quite appreciably. The libration and translation contributions to the thermal expansion of pure C60 are separated. The experimental results on the thermal expansion are used to obtain the Debye temperature of pure C60. The effects observed are tentatively interpreted.
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5.
  • Aleksandrovskii, A. N., et al. (författare)
  • Thermal expansion of single-crystal fullerite C60 at helium temperatures
  • 2000
  • Ingår i: Low temperature physics (Woodbury, N.Y., Print). - 1063-777X. ; 26:1, s. 75-80
  • Tidskriftsartikel (refereegranskat)abstract
    • The thermal expansion of single-crystal fullerite C60 has been studied in the range of liquid-helium temperatures (2-10 K). At temperatures below ~4.5 K the thermal expansion of fullerite C60 becomes negative, in agreement with the previous results on polycrystalline materials. A qualitative explanation of the results is proposed
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6.
  • Bagatskii, M.I., et al. (författare)
  • Low-temperature dynamics of matrix isolated methane molecules in fullerite C60. The heat capacity, isotope effects
  • 2014
  • Ingår i: Low temperature physics (Woodbury, N.Y., Print). - American Institute of Physics (AIP). - 1063-777X. ; 40:8, s. 678-684
  • Tidskriftsartikel (refereegranskat)abstract
    • The heat capacity of the interstitial solid solution (CH4)0.4C60 has been investigated in the temperature interval 1.4–120 K. The contribution of CH4 molecules to the heat capacity of the solution has been separated. The contributions of CH4 and CD4 molecules to the heat capacity of the solutions (CH4)0.40C60 and (CD4)0.40C60 have been compared. It is found that above 90 K the character of the rotational motion of CH4 and CD4 molecules changes from libration to hindered rotation. In the interval 14–35 K the heat capacities of CH4 and CD4 molecules are satisfactorily described by contributions of the translational and libration vibrations, as well as the tunnel rotation for the equilibrium distribution of the nuclear spin species. The isotope effect is due to mainly the difference in the frequencies of local translational and libration vibrations of molecules CH4 and CD4. The contribution of the tunnel rotation of the CH4 and CD4 molecules to the heat capacity is dominant below 8 K. The isotopic effect is caused by the difference between both the conversion rates and the rotational spectra of the nuclear spin species of CH4 and CD4 molecules. The conversion rate of CH4 molecules is several times lower than that of CD4 ones. Weak features observed in the curves of temperature dependencies of the heat capacity of CH4 and CD4 molecules near 6 and 8 K, respectively, are most likely a manifestation of first-order polyamorphic phase transitions in the orientational glasses of these solutions.
7.
  • Bagatskii, M. I., et al. (författare)
  • Low-temperature heat capacity of fullerite C-60 doped with deuteromethane
  • 2012
  • Ingår i: Low temperature physics (Woodbury, N.Y., Print). - Melville, NY : American Institute of Physics (AIP). - 1063-777X. ; 38:1, s. 67-73
  • Tidskriftsartikel (refereegranskat)abstract
    • The heat capacity C of fullerite doped with deuteromethane (CD4)(0.4)(C-60) has been investigated in the temperature interval 1.2-120K. The contribution Delta C-CD4 of the CD4 molecules to the heat capacity C has been isolated. It is shown that at T approximate to 120K the rotational motion of CD4 molecules in the octahedral voids of the C-60 lattice is weakly hindered. When the temperature is lowered to 80K, the rotational motion of the CD4 molecules changes from weakly hindered rotation to libration. In the range T = 1.2-30 K, Delta C-CD4 is described quite accurately by the sum of contributions from the translational and librational vibrations and tunneling rotation of CD4 molecules. The contribution of tunneling rotation to the heat capacity Delta C-CD4(T) is dominant below 5K. The effect of nuclear-spin conversion of the CD4 molecules on the heat capacity has been observed and the characteristic times for nuclear spin conversion between the lowest levels of the A- and T-species of CD4 molecules at T < 5K have been estimated. A feature observed in Delta C-CD4(T) near T = 5.5K is most likely a manifestation of a first-order phase transition in the orientational glass form of the solution. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3677237]
8.
  • Bagatskii, M.I., et al. (författare)
  • The specific heat and the radial thermal expansion of bundles of single-walled carbon nanotubes
  • 2012
  • Ingår i: Low temperature physics (Woodbury, N.Y., Print). - American Institute of Physics (AIP). - 1063-777X. ; 38:6, s. 523-528
  • Tidskriftsartikel (refereegranskat)abstract
    • The specific heat at constant pressure C(T) of bundles of single-walled carbon nanotubes (SWNTs) closed at their ends has been investigated in the temperature interval of 2–120 K. It is found that the curve C(T) has features near 5, 36, 80, and 100 K. The experimental results on the C(T) and the radial thermal expansion coefficient αR(T) of bundles of SWNTs oriented perpendicular to the sample axis have been compared. It is found that the curves C(T) and αR(T) exhibit a similar temperature behavior at T > 10 K. The temperature dependence of the Grüneisen coefficient γ(T) has been calculated. The curve γ(T) also has a feature near 36 K. Above 36 K the Grüneisen coefficient is practically independent of temperature (γ ≈ 4). Below 36 K, γ(T) decreases monotonically with lowering temperature and becomes negative at T < 6 K.
9.
  • Balkashin, O. P., et al. (författare)
  • Nonstationary magnetization dynamics of point contacts with a single ferromagnetic film
  • 2009
  • Ingår i: Low temperature physics (Woodbury, N.Y., Print). - 1063-777X. ; 35:8-9, s. 693-701
  • Tidskriftsartikel (refereegranskat)abstract
    • The electric conductivity of point nanocontacts between 5, 10, and 100 nm thick ferromagnetic (F) cobalt films and a nonmagnetic (N) metal (copper or silver) needle is investigated. Two fundamentally different mechanisms for the formation of the response, signal to microwave irradiation have been observed for the first time. One mechanism is due to the effect of the rectification of high frequency ac current on the nonlinearity of the current-voltage characteristics due to the precession of the magnetization under the action of a constant transport current flowing through the contact. The second one is associated with the resonance excitation of the precession of the magnetization vector at the fundamental frequency and its harmonic by an external high-frequency field. The experimental results support a previous contention that a "surface spin valve" whose static and dynamic properties are similar to conventional F-1-N-F-2 spin valve [Nano Letters 7, 927 (2007)] is formed in the experimental F-N nanocontacts.
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10.
  • Barone, A., et al. (författare)
  • Macroscopic quantum phenomena in Josephson structures
  • 2010
  • Ingår i: Low Temperature Physics. - 1063-777X. ; 36:10-11, s. 876-883
  • Tidskriftsartikel (refereegranskat)abstract
    • The Josephson effect is a probe with unparalleled capabilities for the study of a variety of macroscopic quantum phenomena. This is a survey of important achievements and challenging trends, in particular macroscopic quantum tunneling and energy level quantization. We focus on high-T-C superconducting structures and recent research on nanostructures.
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