Comment on: Evidence and Stability Field of fcc Superionic Water Ice Using Static Compression

Weck et al. (1) report on the existence and stability fields of two superionic (SI) phases of H2O ice at high P-T (P-T) conditions, which has been a topic of static and dynamic experiments and theoretical calculations (see Ref. (2) and references therein). They confirm Ref. (2) in that there are two SI phases with bcc and fcc oxygen sublattices with the stability at low- and high-P. However, they report on an extended stability field of fcc-SI ice toward lower T but no sign of it below 57 GPa. Here we argue that the reported phase boundaries of fcc-SI phase are not well experimentally justified due to difficulties to perform adequate X-ray diffraction (XRD) and radiometric measurements.Comment: 2 pages, 2 figures, 2 reference

Cryopreservation of Atlantic sturgeon Acipenser sturio L., 1758 sperm: First results and associated problems

We present our attempts to adapt the established cryopreservation techniques for sturgeon sperm to Acipenser sturio L., 1758, using the sperm of a wild male which matured in vivo. The sperm, from a ripe male caught in the Gironde estuary in 1996 and obtained 4 h after its catch and transport, was diluted 1:1 with media containing 56.0-76.0% tris-HCl-buffer (49.5 mM tris(oxymethyl)aminomethane) (pH 8.0), 14.4-24.0% dimethylsulfoxide and 9.6-20.0% egg yolk. The suspension was poured into 1.5 ml tubes, sealed and frozen in -196 °C liquid nitrogen vapour in a three-stage programme. Thawing took place in a 40 °C water bath. The motility of thawed sperm was 10-15%, whereas the motility in native sperm before cryopreservation was 50 %. After one month storage time in liquid nitrogen, sperm was thawed and used for fertilization of sterlet Acipenser ruthenus L., 1758 eggs with the help of two activator media. After fertilization in a medium containing 3.1 mM tris(oxymethyl)aminomethane, 5.3 mM NaCl and 58.3 mM sucrose, 38.3% of the embryos were developing on the second day, compared with 23.2% when activator without sucrose was used. In the control group, fertilization of sterlet eggs with fresh sterlet sperm resulted in 43 % developing embryos.Presentamos nuestros intentos de adaptar las técnicas establecidas de criopreservación al esperma de Acipenser sturio L., 1758, usando el esperma de un macho silvestre madurado in vivo. El esperma, procedente de un macho maduro capturado en el estuario del Gironda en 1996 y obtenido cuatro horas después de su captura y transporte, fue diluido 1:1 en un medio que contenía 56.0-76.0% tris-HCl-buffer (49.5 mM tris(oximetil)aminometano) (pH 8.0), 14.4-24.0% dimetilsulfóxido y 9.6-20.0% yema de huevo. La suspensión fue vertida en tubos de 1.5 ml, sellada y congelada en nitrógeno líquido a -196 °C en un programa de tres fases. La descongelación tuvo lugar en un baño de agua a 40 °C. La movilidad del esperma descongelado fue del 10-15%, mientras que la movilidad del esperma nativo antes de la criopreservación fue del 50 %. Después de un mes de almacenamiento en nitrógeno líquido, el esperma fue descongelado y empleado para la fertilización de huevos de esterlete Acipenser ruthenus L., 1758 con la ayuda de dos medios activadores. Después de la fertilización en un medio conteniendo 3.1 mM tris(oximetil)aminometano, 5.3 mM NaCl y 58.3 mM sacarosa, el 38.3% de los embriones se desarrollaron al segundo día, frente al 23.2% obtenido cuando se usó un activador sin sacarosa. En el grupo control, la fertilización de huevos de esterlete con esperma fresco de esterlete produjo un 43 % de embriones desarrollados.Instituto Español de Oceanografí

Poisson's ratio in cryocrystals under pressure

We present results of lattice dynamics calculations of Poisson's ratio (PR) for solid hydrogen and rare gas solids (He, Ne, Ar, Kr and Xe) under pressure. Using two complementary approaches - the semi-empirical many-body calculations and the first-principle density-functional theory calculations we found three different types of pressure dependencies of PR. While for solid helium PR monotonically decreases with rising pressure, for Ar, Kr, and Xe it monotonically increases with pressure. For solid hydrogen and Ne the pressure dependencies of PR are non-monotonic displaying rather deep minimums. The role of the intermolecular potentials in this diversity of patterns is discussed.Comment: Fizika Nizkikh Temperatur 41, 571 (2015

Inflationary cosmology of the extreme cosmic string

Starting with a study of the cosmological solution to the Einstein equations for the internal spacetime of an extreme supermassive cosmic string kink, and by evaluating the probability measure for the formation of such a kink in semiclassical approximation using a minisuperspace with the appropriate symmetry, we have found a set of arguments in favor of the claim that the kinked extreme string can actually be regarded as a unbounded chain of pairs of Planck- sized universes. Once one such universe pairs is created along a primordial phase transition at the Planck scale, it undergoes an endless process of continuous self-regeneration driven by chaotic inflation in each of the universes forming the pair.Comment: 15 pages, RevTex, to appear in Int. J. Mod. Phys.

Two-Loop Bhabha Scattering in QED

In the context of pure QED, we obtain analytic expressions for the contributions to the Bhabha scattering differential cross section at order alpha^4 which originate from the interference of two-loop photonic vertices with tree-level diagrams and from the interference of one-loop photonic diagrams amongst themselves. The ultraviolet renormalization is carried out. The IR-divergent soft-photon emission corrections are evaluated and added to the virtual cross section. The cross section obtained in this manner is valid for on-shell electrons and positrons of finite mass, and for arbitrary values of the center of mass energy and momentum transfer. We provide the expansion of our results in powers of the electron mass, and we compare them with the corresponding expansion of the complete order alpha^4 photonic cross section, recently obtained in hep-ph/0501120. As a by-product, we obtain the contribution to the Bhabha scattering differential cross section of the interference of the two-loop photonic boxes with the tree-level diagrams, up to terms suppressed by positive powers of the electron mass. We evaluate numerically the various contributions to the cross section, paying particular attention to the comparison between exact and expanded results.Comment: 35 pages, 18 figure