Quantum-fluctuation-induced repelling interaction of quantum string between walls

Quantum string, which was brought into discussion recently as a model for the stripe phase in doped cuprates, is simulated by means of the density-matrix-renormalization-group method. String collides with adjacent neighbors, as it wonders, owing to quantum zero-point fluctuations. The energy cost due to the collisions is our main concern. Embedding a quantum string between rigid walls with separation d, we found that for sufficiently large d, collision-induced energy cost obeys the formula \sim exp (- A d^alpha) with alpha=0.808(1), and string's mean fluctuation width grows logarithmically \sim log d. Those results are not understood in terms of conventional picture that the string is `disordered,' and only the short-wave-length fluctuations contribute to collisions. Rather, our results support a recent proposal that owing to collisions, short-wave-length fluctuations are suppressed, but instead, long-wave-length fluctuations become significant. This mechanism would be responsible for stabilizing the stripe phase

Two-loop HTL Thermodynamics with Quarks

We calculate the quark contribution to the free energy of a hot quark-gluon plasma to two-loop order using hard-thermal-loop (HTL) perturbation theory. All ultraviolet divergences can be absorbed into renormalizations of the vacuum energy and the HTL quark and gluon mass parameters. The quark and gluon HTL mass parameters are determined self-consistently by a variational prescription. Combining the quark contribution with the two-loop HTL perturbation theory free energy for pure-glue we obtain the total two-loop QCD free energy. Comparisons are made with lattice estimates of the free energy for N_f=2 and with exact numerical results obtained in the large-N_f limit.Comment: 33 pages, 6 figure

Microsatellite diversity and chromosome number in natural populations of Trifolium riograndense Burkart

Twenty eight natural populations of Trifolium riograndense Burkart, an important forage legume from native pastures of the state of Rio Grande do Sul, Brazil, were evaluated for genetic diversity with eight Simple Sequences Repeats (SSR) markers. Chromosome numbers were also determined. The eight markers were polymorphic, with 35 alleles and an average of 4.37 alleles per locus, and Polymorphism Information Content (PIC) between 0.48 and 0.80. Group analysis based on Jaccard´s similarity coefficient separated the 28 accessions in nine groups, with an average genetic similarity of 0.44, indicating a high genetic variability among the populations. No evident relation between genetic distance and geographical origin was detected. The chromosome number of 2n=2x=16 was found in all populations, indicating lack of intraspecific variability for chromosome number in the species. This information on diversity can be used in conservation strategies as well as in genetic breeding programs of this species

An overwintering cover crop increases inoculum of VAM fungi in agricultural soil

AbstractWe conducted a field experiment within a low-input reduced tillage trial to determine how a cover crop affects inoculum levels of vesicular-arbuscular mycorrhizal (VAM) fungi. Plots with and without the hairy vetch cover crop were established on September 30, 1993, under moldboard plow (MP), chisel-disk (CD), and no-till (NT) treatments in low-input (LI) management, and MP in conventional (CONV) management. We conducted a 3-week colonization assay in the greenhouse with bahiagrass seedlings to assess the relative colonization potential of the soils in the fall and following spring. Hairy vetch roots were colonized by indigenous VAM fungi by 65 days after planting, with plants from NT being more colonized than plants from MP or CD plots. Spore populations were greater in the LI than in the CONV system. The beneficial effect of the cover crop on VAM spore populations in soil was manifested in the spring, with theGlomustype group more abundant in plots with cover than without it. The greenhouse bioassay showed that colonization potential of spring 1994 soil samples was higher in plots with cover than without cover for both the LI and CONV systems. Just one season of an overwintering cover crop of hairy vetch increased the inoculum of VAM fungi the following spring before the next cash crop was planted.</jats:p