The utopian tradition: A comparison of The Republic and Utopia with James Hilton\u27s \u27Lost Horizon

Utopia -- the concept more than the word -- has captured the imagination and fostered the hopes of men through thousands of years of recorded history. Behind the concept, one which various ages have redefined for their own particular situations, lies the nascent belief that humankind, working in harmony and unison, can create a better world and achieve maximum progress towards happiness

Anomalous Spin Dynamics in Doped Quantum Antiferromagnets

Finite-temperature spin dynamics in planar t-J model is studied using the method based on the Lanczos diagonalization of small systems. Dynamical spin structure factor at moderate dopings shows the coexistence of free-fermion-like and spin-fluctuation timescales. At T<J, the low-frequency and static susceptibility show pronounced T dependence, supporting a scenario, related to the marginal Fermi-liquid one, for the explanation of neutron-scattering and NMR-relaxation experiments in cuprates. Calculated NMR relaxation rates reasonably reproduce experimental ones.Comment: 10 pages + 4 figures, Postscript in uuencoded compressed tar file, IJS-TP-94/2

Neutral interstellar He parameters in front of the heliosphere 1994--2007

Analysis of IBEX measurements of neutral interstellar He flux brought the inflow velocity vector different from the results of earlier analysis of observations from GAS/Ulysses. Recapitulation of results on the helium inflow direction from the past ~40 years suggested that the inflow direction may be changing with time. We reanalyze the old Ulysses data and reprocess them to increase the accuracy of the instrument pointing to investigate if the GAS observations support the hypothesis that the interstellar helium inflow direction is changing. We employ a similar analysis method as in the analysis of the IBEX data. We seek a parameter set that minimizes reduced chi-squared, using the Warsaw Test Particle Model for the interstellar He flux at Ulysses with a state of the art model of neutral He ionization in the heliosphere, and precisely reproducing the observation conditions. We also propose a supplementary method of constraining the parameters based on cross-correlations of parameters obtained from analysis of carefully selected subsets of data. We find that the ecliptic longitude and speed of interstellar He are in a very good agreement with the values reported in the original GAS analysis. We find, however, that the temperature is markedly higher. The 3-seasons optimum parameter set is lambda = 255.3, beta = 6, v = 26.0 km/s, T = 7500 K. We find no evidence that it is varying with time, but the uncertainty range is larger than originally reported. The originally-derived parameters of interstellar He from GAS are in good agreement with presently derived, except for the temperature, which seems to be appreciably higher, in good agreement with interstellar absorption line results. While the results of the present analysis are in marginal agreement with the earlier reported results from IBEX, the most likely values from the two analyses differ for reasons that are still not understood.Comment: submitted for publication in Astronomy & Astrophysic

NMR relaxation in half-integer antiferromagnetic spin chains

Nuclear relaxation in half-integer spin chains at low temperatures (T << J, the antiferromagnetic exchange constant) is dominated by dissipation from a gas of thermally-excited, overdamped, spinons. The universal low temperature dependence of the relaxation rates $1/T_1$ and $1/T_{2G}$ is computed.Comment: 7 pages, 1 uuencoded postscript figure appende

Coherent and Incoherent Dynamic Structure Function of the Free Fermi Gas

A detailed calculation of the coherent and incoherent dynamic structure functions of the free Fermi gas, starting from their expressions in terms of the one- and semi-diagonal two-body density matrices, is derived and discussed. Their behavior and evolution with the momentum transfer is analyzed, and particular attention is devoted to the contributions that both functions present at negative energies. Finally, an analysis of the energy weighted sum rules satisfied by both responses is also performed. Despite of the simplicity of the model, some of the conclusions can be extended to realistic systems.Comment: LaTeX, 3 figure