Results 1 - 10 of 30068
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[en] We consider bond percolation on where edges of are open with probability and edges of are open with probability q, independently of all others. We obtain bounds for the critical curve in (p, q), with p close to the critical threshold . The results are related to the so-called dimensional crossover from to .
[en] We study the phase diagram of the extended Hubbard model in the atomic limit. At zero temperature, the phase diagram decomposes into six regions: three with homogeneous phases (characterized by particle densities ρ=0, 1 and 2 and staggered charge density Δ=0) and three with staggered phases (characterized by the densities ρ=1/2, 1 and 3/2 and staggered densities vertical bar Δ vertical bar = 1/2, 1, and 1/2). Here we use Pirogov-Sinai theory to analyse the details of the phase diagram of this model at low temperatures. In particular, we show that for any sufficiently low non-zero temperature the three staggered regions merge into one staggered region S, without any phase transitions (analytic free energy and staggered order parameter Δ) within S. (author)
[en] We investigated a LaFeAsO single crystal by means of synchrotron Mössbauer spectroscopy under pressure up to 7.5 GPa and down to 13 K and provide a microscopic phase diagram. A continuous suppression of the magnetic hyperfine field with increasing pressure was found and it completely vanishes at 7.5 GPa which is in contrast to the behaviour in polycrystalline samples where the magnetic order vanishes at 20 GPa. We discuss the sample dependence of the magnetic order among different single and polycrystalline samples and its relationship to the structural parameters.
[en] The phase diagram of the Rb-O system has been examined up to 28 at% oxygen and below 2000C. A eutectic point was found between rubidium and a rubidium suboxide (either Rb6O or Rb9O2) at 10 at% oxygen and -140C. Three peritectic reactions were found: above 12 at% oxygen at -110C, above 14 at% oxygen at 200C, and above 18 at% oxygen at 1160C. However, the composition of the rubidium suboxide that reveals the peritectic reaction could not be obtained. Oxygen solubility in rubidium above the melting point was equal to or greater than 3 wt%. With increasing oxygen concentration in the Rb-O mixture, the examination became more difficult. This difficulty appeared to be due to an intrinsic property of the Rb-O system, i.e. disproportionation of rubidium suboxide in the system. (orig./RK)
[en] The spin-1 Ising model with bilinear and bi quadratic exchange interactions and single-ion crystal field is solved on the Bethe lattice using exact recursion equations. The general procedure of investigation of critical properties is discussed and a full set of phase diagrams are constructed for both positive and negative bi quadratic couplings. A comparison is made with the results of other approximation schemes. (author)