1,100 research outputs found
Crumpling transition of the triangular lattice without open edges: effect of a modified folding rule
Folding of the triangular lattice in a discrete three-dimensional space is
investigated by means of the transfer-matrix method. This model was introduced
by Bowick and co-workers as a discretized version of the polymerized membrane
in thermal equilibrium. The folding rule (constraint) is incompatible with the
periodic-boundary condition, and the simulation has been made under the
open-boundary condition. In this paper, we propose a modified constraint, which
is compatible with the periodic-boundary condition; technically, the
restoration of translational invariance leads to a substantial reduction of the
transfer-matrix size. Treating the cluster sizes L \le 7, we analyze the
singularities of the crumpling transitions for a wide range of the bending
rigidity K. We observe a series of the crumpling transitions at K=0.206(2),
-0.32(1), and -0.76(10). At each transition point, we estimate the latent heat
as Q=0.356(30), 0.08(3), and 0.05(5), respectively
Folding of the triangular lattice in a discrete three-dimensional space: Crumpling transitions in the negative-bending-rigidity regime
Folding of the triangular lattice in a discrete three-dimensional space is
studied numerically. Such ``discrete folding'' was introduced by Bowick and
co-workers as a simplified version of the polymerized membrane in thermal
equilibrium. According to their cluster-variation method (CVM) analysis, there
appear various types of phases as the bending rigidity K changes in the range
-infty < K < infty. In this paper, we investigate the K<0 regime, for which the
CVM analysis with the single-hexagon-cluster approximation predicts two types
of (crumpling) transitions of both continuous and discontinuous characters. We
diagonalized the transfer matrix for the strip widths up to L=26 with the aid
of the density-matrix renormalization group. Thereby, we found that
discontinuous transitions occur successively at K=-0.76(1) and -0.32(1).
Actually, these transitions are accompanied with distinct hysteresis effects.
On the contrary, the latent-heat releases are suppressed considerably as
Q=0.03(2) and 0.04(2) for respective transitions. These results indicate that
the singularity of crumpling transition can turn into a weak-first-order type
by appreciating the fluctuations beyond a meanfield level
Identification of the First Functional Toxin-Antitoxin System in Streptomyces
Toxin-antitoxin (TA) systems are widespread among the plasmids and genomes of bacteria and archaea. This work reports the first description of a functional TA system in Streptomyces that is identical in two species routinely used in the laboratory: Streptomyces lividans and S. coelicolor. The described system belongs to the YefM/YoeB family and has a considerable similarity to Escherichia coli YefM/YoeB (about 53% identity and 73% similarity). Lethal effect of the S. lividans putative toxin (YoeBsl) was observed when expressed alone in E. coli SC36 (MG1655 ΔyefM-yoeB). However, no toxicity was obtained when co-expression of the antitoxin and toxin (YefM/YoeBsl) was carried out. The toxic effect was also observed when the yoeBsl was cloned in multicopy in the wild-type S. lividans or in a single copy in a S. lividans mutant, in which this TA system had been deleted. The S. lividans YefM/YoeBsl complex, purified from E. coli, binds with high affinity to its own promoter region but not to other three random selected promoters from Streptomyces. In vivo experiments demonstrated that the expression of yoeBsl in E. coli blocks translation initiation processing mRNA at three bases downstream of the initiation codon after 2 minutes of induction. These results indicate that the mechanism of action is identical to that of YoeB from E. coli
Identification of the First Functional Toxin-Antitoxin System in Streptomyces
Toxin-antitoxin (TA) systems are widespread among the plasmids and genomes of bacteria and archaea. This work reports the first description of a functional TA system in Streptomyces that is identical in two species routinely used in the laboratory: Streptomyces lividans and S. coelicolor. The described system belongs to the YefM/YoeB family and has a considerable similarity to Escherichia coli YefM/YoeB (about 53% identity and 73% similarity). Lethal effect of the S. lividans putative toxin (YoeBsl) was observed when expressed alone in E. coli SC36 (MG1655 ΔyefM-yoeB). However, no toxicity was obtained when co-expression of the antitoxin and toxin (YefM/YoeBsl) was carried out. The toxic effect was also observed when the yoeBsl was cloned in multicopy in the wild-type S. lividans or in a single copy in a S. lividans mutant, in which this TA system had been deleted. The S. lividans YefM/YoeBsl complex, purified from E. coli, binds with high affinity to its own promoter region but not to other three random selected promoters from Streptomyces. In vivo experiments demonstrated that the expression of yoeBsl in E. coli blocks translation initiation processing mRNA at three bases downstream of the initiation codon after 2 minutes of induction. These results indicate that the mechanism of action is identical to that of YoeB from E. coli
Vacuum type of SU(2) gluodynamics in maximally Abelian and Landau gauges
The vacuum type of SU(2) gluodynamics is studied using Monte-Carlo
simulations in maximally Abelian (MA) gauge and in Landau (LA) gauge, where the
dual Meissner effect is observed to work. The dual Meissner effect is
characterized by the coherence and the penetration lengths. Correlations
between Wilson loops and electric fields are evaluated in order to measure the
penetration length in both gauges. The coherence length is shown to be fixed in
the MA gauge from measurements of the monopole density around the static
quark-antiquark pair. It is also shown numerically that a dimension 2 gluon
operator A^+A^-(s) and the monopole density has a strong correlation as
suggested theoretically. Such a correlation is observed also between the
monopole density and A^2(s)= A^+A^-(s) + A^3A^3(s) condensate if the remaining
U(1) gauge degree of freedom is fixed to U(1) Landau gauge (U1LA). The
coherence length is determined numerically also from correlations between
Wilson loops and A^+A^-(s) and A^2(s) in MA + U1LA gauge. Assuming that the
same physics works in the LA gauge, we determine the coherence length from
correlations between Wilson loops and A^2(s). Penetration lengths and coherence
lengths in the two gauges are almost the same. The vacuum type of the
confinement phase in both gauges is near to the border between the type 1 and
the type 2 dual superconductors.Comment: 13 pages, 22 figures, RevTeX 4 styl
Superconductivity suppression of Ba0.5K0.5Fe2-2xM2xAs2 single crystals by substitution of transition-metal (M = Mn, Ru, Co, Ni, Cu, and Zn)
We investigated the doping effects of magnetic and nonmagnetic impurities on
the single-crystalline p-type Ba0.5K0.5Fe2-2xM2xAs2 (M = Mn, Ru, Co, Ni, Cu and
Zn) superconductors. The superconductivity indicates robustly against impurity
of Ru, while weakly against the impurities of Mn, Co, Ni, Cu, and Zn. However,
the present Tc suppression rate of both magnetic and nonmagnetic impurities
remains much lower than what was expected for the s\pm-wave model. The
temperature dependence of resistivity data is observed an obvious low-T upturn
for the crystals doped with high-level impurity, which is due to the occurrence
of localization. Thus, the relatively weak Tc suppression effect from Mn, Co,
Ni, Cu, and Zn are considered as a result of localization rather than
pair-breaking effect in s\pm-wave model.Comment: 8 pages, 9 figures, to be published in Phys. Rev.
Sequential activation of NKT cells and NK cells provides effective innate immunotherapy of cancer
The CD1d reactive glycolipid, α-galactosylceramide (α-GalCer), potently activates T cell receptor-α type I invariant NKT cells that secondarily stimulate the proliferation and activation of other leukocytes, including NK cells. Here we report a rational approach to improving the antitumor activity of α-GalCer by using delayed interleukin (IL)-21 treatment to mature the α-GalCer–expanded pool of NK cells into highly cytotoxic effector cells. In a series of experimental and spontaneous metastases models in mice, we demonstrate far superior antitumor activity of the α-GalCer/IL-21 combination above either agent alone. Superior antitumor activity was critically dependent upon the increased perforin-mediated cytolytic activity of NK cells. Transfer of α-GalCer–pulsed dendritic cells (DCs) followed by systemic IL-21 caused an even more significant reduction in established (day 8) metastatic burden and prolonged survival. In addition, this combination prevented chemical carcinogenesis more effectively. Combinations of IL-21 with other NK cell–activating cytokines, such as IL-2 and IL-12, were much less effective in the same experimental metastases models, and these cytokines did not substitute effectively for IL-21 in combination with α-GalCer. Overall, the data suggest that NK cell antitumor function can be enhanced greatly by strategies that are designed to expand and differentiate NK cells via DC activation of NKT cells
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