3,899 research outputs found

    Thermoelectric figure of merit of tau-type conductors of several donors

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    Dimensionless thermoelectric figure of merit ZTZT is investigated for two-dimensional organic conductors τ(EDOS,SDMEDTTTF)2(AuI2)1+y\tau-(EDO-S,S-DMEDT-TTF)_2(AuI_2)_{1+y}, τ\tau-(EDT-S,S-DMEDT-TTF)_2(AuI_2)_{1+y}and and \tau(PS,SDMEDTTTF)2(AuI2)1+y-(P-S,S-DMEDT-TTF)_2(AuI_2)_{1+y} (y0.875y \le 0.875), respectively. The ZTZT values were estimated by measuring electrical resistivity, thermopower and thermal conductivity simultaneously. The largest ZTZT is 2.7 ×\times 102^{-2} at 155 K for τ(EDTS,SDMEDTTTF)2(AuI2)1+y\tau-(EDT-S,S-DMEDT-TTF)_2(AuI_2)_{1+y}, 1.5 ×\times 102^{-2} at 180 K for τ(EDOS,SDMEDTTTF)2(AuI2)1+y\tau-(EDO-S,S-DMEDT-TTF)_2(AuI_2)_{1+y} and 5.4 ×\times 103^{-3} at 78 K for τ(PS,SDMEDTTTF)2(AuI2)1+y\tau-(P-S,S-DMEDT-TTF)_2(AuI_2)_{1+y}, respectively. Substitution of the donor molecules fixing the counter anion revealed EDT-S,S-DMEDT-TTF is the best of the three donors to obtain larger ZTZT.Comment: proceedings of ISCOM 2009 (to be published in Physica B

    Bosenova collapse of axion cloud around a rotating black hole

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    Motivated by possible existence of stringy axions with ultralight mass, we study the behavior of an axion field around a rapidly rotating black hole (BH) obeying the sine-Gordon equation by numerical simulations. Due to superradiant instability, the axion field extracts the rotational energy of the BH and the nonlinear self-interaction becomes important as the field grows larger. We present clear numerical evidences that the nonlinear effect leads to a collapse of the axion cloud and a subsequent explosive phenomena, which is analogous to the "bosenova" observed in experiments of Bose-Einstein condensate. The criterion for the onset of the bosenova collapse is given. We also discuss the reason why the bosenova happens by constructing an effective theory of a wavepacket model under the nonrelativistic approximation.Comment: 38 pages, 18 figure

    Temperature Chaos and Bond Chaos in the Edwards-Anderson Ising Spin Glass : Domain-Wall Free-Energy Measurements

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    Domain-wall free-energy δF\delta F, entropy δS\delta S, and the correlation function, CtempC_{\rm temp}, of δF\delta F are measured independently in the four-dimensional ±J\pm J Edwards-Anderson (EA) Ising spin glass. The stiffness exponent θ\theta, the fractal dimension of domain walls dsd_{\rm s} and the chaos exponent ζ\zeta are extracted from the finite-size scaling analysis of δF\delta F, δS\delta S and CtempC_{\rm temp} respectively well inside the spin-glass phase. The three exponents are confirmed to satisfy the scaling relation ζ=ds/2θ\zeta=d_{\rm s}/2-\theta derived by the droplet theory within our numerical accuracy. We also study bond chaos induced by random variation of bonds, and find that the bond and temperature perturbations yield the universal chaos effects described by a common scaling function and the chaos exponent. These results strongly support the appropriateness of the droplet theory for the description of chaos effect in the EA Ising spin glasses.Comment: 4 pages, 6 figures; The title, the abstract and the text are changed slightl

    Scaling Analysis of Domain-Wall Free-Energy in the Edwards-Anderson Ising Spin Glass in a Magnetic Field

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    The stability of the spin-glass phase against a magnetic field is studied in the three and four dimensional Edwards-Anderson Ising spin glasses. Effective couplings and effective fields associated with length scale L are measured by a numerical domain-wall renormalization group method. The results obtained by scaling analysis of the data strongly indicate the existence of a crossover length beyond which the spin-glass order is destroyed by field H. The crossover length well obeys a power law of H which diverges as H goes to zero but remains finite for any non-zero H, implying that the spin-glass phase is absent even in an infinitesimal field. These results are well consistent with the droplet theory for short-range spin glasses.Comment: 4 pages, 5 figures; The text is slightly changed, the figures 3, 4 and 5 are changed, and a few references are adde

    Absolute Transition Probabilities of Lines in the Spectra of Astrophysical Atoms, Molecules, and Ions

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    Progress in the investigation of absolute transition probabilities (A-values or F values) for ultraviolet lines is reported. A radio frequency ion trap was used for measurement of transition probabilities for intersystem lines seen in astronomical spectra. The intersystem line at 2670 A in Al II, which is seen in pre-main sequence stars and symbiotic stars, was studied

    Absolute absorption cross sections of ozone at 300 K, 228 K and 195 K in the wavelength region 185-240 nm

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    An account is given of progress of work on absorption cross section measurements of ozone at 300 K, 228 K and 195 K in the wavelength region 185-240 nm. In this wavelength region, the penetration of solar radiation into the Earth's atmosphere is controlled by O2 and O3. The transmitted radiation is available to dissociate trace species such as halocarbons and nitrous oxide. We have recently measured absolute absorption cross sections of O3 in the wavelength region 240-350 nm (Freeman et al., 1985; Yoshino et al., 1988). We apply these proven techniques to the determination of the absorption cross section of O3 at 300 K, 228 K and 195 K throughout the wavelength region 185-240 nm. A paper titled 'Absolute Absorption Cross Section Measurements of Ozone in the Wavelength Region 185-254 nm and the Temperature Dependence' has been submitted for publication in the Journal of Geophysical Research