Comment on "Hole-Burning Experiments within Glassy Models with Infinite Range Interactions"

Comment on: L.F. Cugliandolo and J.L. Iguain; Phys. Rev. Lett. {\bf 85} 3448 (2000)Comment: 1 page, RevTe

Bounds on the basic physical parameters for anisotropic compact general relativistic objects

We derive upper and lower limits for the basic physical parameters (mass-radius ratio, anisotropy, redshift and total energy) for arbitrary anisotropic general relativistic matter distributions in the presence of a cosmological constant. The values of these quantities are strongly dependent on the value of the anisotropy parameter (the difference between the tangential and radial pressure) at the surface of the star. In the presence of the cosmological constant, a minimum mass configuration with given anisotropy does exist. Anisotropic compact stellar type objects can be much more compact than the isotropic ones, and their radii may be close to their corresponding Schwarzschild radii. Upper bounds for the anisotropy parameter are also obtained from the analysis of the curvature invariants. General restrictions for the redshift and the total energy (including the gravitational contribution) for anisotropic stars are obtained in terms of the anisotropy parameter. Values of the surface redshift parameter greater than two could be the main observational signature for anisotropic stellar type objects.Comment: 18 pages, no figures, accepted for publication in CQ

Origin of the tetragonal-to-orthorhombic (nematic) phase transition in FeSe: a combined thermodynamic and NMR study

The nature of the tetragonal-to-orthorhombic structural transition at $T_s\approx90$ K in single crystalline FeSe is studied using shear-modulus, heat-capacity, magnetization and NMR measurements. The transition is shown to be accompanied by a large shear-modulus softening, which is practically identical to that of underdoped Ba(Fe,Co)$_2$As$_2$, suggesting very similar strength of the electron-lattice coupling. On the other hand, a spin-fluctuation contribution to the spin-lattice relaxation rate is only observed below $T_s$. This indicates that the structural, or "nematic", phase transition in FeSe is not driven by magnetic fluctuations

Self inclusion in a calix[5]arene structure; structure of the cone conformer of a pentahydroxy-p-tert-butylcalix[5]arene

The pentahydroxy-p-tert-butylcalix[5]arene, 5,11,17,- 23,29-penta-tert-butylhexacyclo[25.3.1.13,7.19,13.115,19._ 121,25 ] pentatriaconta- 1 (31),3,5,7 (35),9,11,13(34), 15,17,- 19(33),21,23,25 (32),27,29-pentadecaene-31,32,3 3,34,- 35-pentaol-n-hexane (1/0.3), C55H70Os.0.3C6HI4 (I), adopts an open distorted chalice-shaped conformation in the solid state, primarily through O--H...O intramolecular hydrogen bonding involving all of the aromatic hydroxyl groups. The five phenolic O.- .O separations are in the range 2.735 (7)-2.880 (8) ,~ [mean 2.793 (8) ,4,], with all hydroxyl H atoms disordered equally over two sites. The aromatic rings are tilted back from the calixarene cavity producing a pentagonal-shaped cavity in which the tert-butyl group of a neighboring calix[5]arene related by a c-glide is enclathrated. This self-inclusion process extends through the lattice as a one-dimensional molecular 'zipper'

Ion hopping in crystalline and glassy spodumene LiAlSi2O6: Li7 spin-lattice relaxation and Li7 echo NMR spectroscopy

Nuclear magnetic resonance spectroscopy was used to study polycrystalline β-spodumene (β−LiAlSi2O6) as well as glassy specimens with the same chemical composition. 7Li spin-lattice relaxation measurements were carried out in a broad temperature range and for several Larmor frequencies. In addition to a pronounced rate maximum at high temperatures, stemming from the long-range Li motion in these aluminosilicates, we found a weak maximum in the crystalline modification near 120K. The latter result confirms the existence of a local double-well structure in which the Li ions reside. The ionic motion was also monitored by solid- and stimulated-echo spectra as well as by the decay of the Jeener-Broekaert echo. Under conditions which are discussed in detail, the latter is a direct measure of the hopping correlation function. For the glass this function was found to decay faster and more stretched than that of the crystal at a given temperature. Furthermore, the relevant barriers against the high-temperature long-range Li motion are larger in the crystal as compared to the glass. © 2005 The American Physical Society