Growth suppression of antibiotic-resistant Salmonella typhimurium DT104 by a non-DT104 strain in vitro

Growth suppression of antibiotic-resistant Salmonella typhimurium DT104 by a non-DT104 strain was investigated in vitro. Chromosomal mutants of eight antibiotic-resistant DT104 strains were generated by sub-culturing on desoxycholate hydrogen sulfide lactose agar containing 25 µg/ml of nalidixic acid. Low counts of each of these mutants (designated as “minority cultures”) were inoculated into 24-h cultures of a non-DT104 S. typhimurium strain (designated as “majority culture”) to test the ability of the majority culture to suppress the multiplication of the minority culture. Multiplication of small numbers of the antibiotic-resistant DT104 strains was significantly (P < 0.05) prevented when the DT104s were added to 24-h brain heart infusion cultures of the non-DT104 strain. This observation has practical implications for the control of the menacing antibiotic-resistant Salmonella typhimurium DT104

Russia: firm entry and survival

Why are there so few new firms in Russia? This paper provides further insights into the specific Russian business landscape and how it impacts the low level of new firm entry. As this paper indicates, internationally comparative data does not provide many clues since in terms of purely formal constraints, Russia fairs comparatively well. However, a deeper analysis uncovers the informal impediments associated with the lack of rule of law, inconsistent enforcement of regulations, regional autonomy and pervasive corruption. These informal constraints form impediments not only for new firm creation but also for firm survival and firm exit. Since not all industries are affected in the same way, this paper includes a comparison between a new and traditional industrial sector: software development and the textile industry

muSR study of the Cu-spin dynamics in the electron-doped high-Tc cuprate of Pr0.86LaCe0.14Cu1-y(Zn,Ni)yO4

Effects of the Zn- and Ni-substitution on the Cu-spin dynamics in the electron-doped Pr0.86LaCe0.14Cu1-y(Zn,Ni)yO4+a-d with y = 0, 0.01, 0.02, 0.05 and different values of the reduced oxygen content d have been studied using zero-field muon-spin-relaxation (muSR) measurements at temperatures down to 2 K. For the as-grown sample (d = 0, y = 0) and the sample with a very small d value (d < 0.01, y = 0), a muon-spin precession due to long-range antiferromagnetic order has been observed. On the other hand, no precession has been observed for moderately oxygen-reduced samples (0.01 < d < 0.09). It has been found that for all the samples of 0.01 < d < 0.09 the asymmetry A(t) (muSR time spectrum) in the long-time region increases with decreasing temperature at low temperatures, suggesting possible slowing-down of the Cu-spin fluctuations. On the other hand, no significant difference between Zn- and Ni-substitution effects on the slowing down of the Cu-spin fluctuations has been observed.Comment: 4 pages, 2 figures, Proceeding of 10th muSR conference 2005, to be published in Physica

Novel Electronic State and Superconductivity in the Electron-Doped High-Tc T'-Superconductors

In this review article, we show our recent results relating to the undoped (Ce-free) superconductivity in the electron-doped high-Tc cuprates with the so-called T' structure. For an introduction, we briefly mention the characteristics of the electron-doped T'-cuprates, including the reduction annealing, conventional phase diagram and undoped superconductivity. Then, our transport and magnetic results and results relating to the superconducting pairing symmetry of the undoped and underdoped T'-cuprates are shown. Collaborating spectroscopic and nuclear magnetic resonance results are also shown briefly. It has been found that, through the reduction annealing, a strongly localized state of carriers accompanied by an antiferromagnetic pseudogap in the as-grown samples changes to a metallic and superconducting state with a short-range magnetic order in the reduced superconducting samples. The formation of the short-range magnetic order due to a very small amount of excess oxygen in the reduced superconducting samples suggests that the T'-cuprates exhibiting the undoped superconductivity in the parent compounds are regarded as strongly correlated electron systems, as well as the hole-doped high-Tc cuprates. We show our proposed electronic structure model to understand the undoped superconductivity. Finally, unsolved future issues of the T'-cuprates are discussed.Comment: 13 pages, 8 figure

Cu-spin dynamics in the overdoped regime of La_2-x_Sr_x_Cu_1-y_Zn_y_O_4_ probed by muon spin relaxation

Muon-spin-relaxation measurements have been performed for the partially Zn-substituted La_2-x_Sr_x_Cu_1-y_Zn_y_O_4_ with y=0-0.10 in the overdoped regime up to x=0.30. In the 3 % Zn-substituted samples up to x=0.27, exponential-like depolarization of muon spins has been observed at low temperatures, indicating Zn-induced slowing-down of the Cu-spin fluctuations. The depolarization rate decreases with increasing x and almost no fast depolarization of muon spins has been observed for x=0.30 where superconductivity disappears. The present results suggest that the dynamical stripe correlations exist in the whole superconducting regime of La_2-x_Sr_x_CuO_4_ and that there is no quantum critical point at x~0.19.Comment: 6 pages, 5 figure

Absence of the impurity-induced magnetic order in the electron-doped high-T_c_ cuprates Pr_0.86_LaCe_0.14_Cu_1-y_(Zn, Ni)_y_O_4_

Zero-field muon-spin-relaxation measurements have been carried out in order to investigate the Zn- and Ni-substitution effects on the Cu-spin dynamics in the electron-doped Pr_0.86_LaCe_0.14_Cu_1-y_(Zn, Ni)_y_O_4+\alpa-\delta_ with y = 0, 0.01, 0.02, 0.05 and different values of the reduced oxygen content \delta(\delta \le 0.09). For the samples with y = 0 and very small \delta values of \delta < 0.01, a muon-spin precession due to the formation of a long-range antiferromagnetic order has been observed at low temperatures below \~ 5 K. For the moderately oxygen-reduced samples of 0.01 \le \delta \le 0.09, on the contrary, no muon-spin precession has been observed and the temperature dependence of the spectra is similar to one another regardless of the y value. That is, no impurity-induced slowing down of the Cu-spin fluctuations has been detected, which is very different from the results of the hole-doped high-T_c_ cuprates. The reason is discussed.Comment: 13 pages, 2 figures, Proceedings of ISS2004 (to be published in Physica C

Weak coupling d-wave BCS superconductivity and unpaired electrons in overdoped La_{2-x}Sr_{x}CuO_{4} single crystals

The low-temperature specific heat (SH) of overdoped La_{2-x}Sr_{x}CuO_{4} single crystals (0.178=<x=<0.290) has been measured. For the superconducting samples (0.178=<x=<0.238), the derived gap values (without any adjusting parameters) approach closely onto the theoretical prediction \Delta_{0}=2.14k_{B}T_{c} for the weak-coupling d-wave BCS superconductivity. In addition, the residual term \gamma(0) of SH at H=0 increases with x dramatically when beyond x~0.22, and finally evolves into the value of a complete normal metallic state at higher doping levels, indicating growing amount of unpaired electrons. We argue that this large \gamma(0) cannot be simply attributed to the pair breaking induced by the impurity scattering, instead the phase separation is possible.Comment: 6 pages, 6 figures; Contents added; Accepted for publication in Phys. Rev.

Magnetic-field effects on the charge-spin stripe order in La-214 high-Tc cuprates

Magnetic-field effects on the charge-spin stripe order in La-214 high-Tc cuprates have been investigated from measurements of the in-plane electrical-resistivity, Rho_ab_. In La_2-x_Ba_x_CuO_4_ with x=0.10 and La_2-x_Sr_x_CuO_4_ with x=0.115 where the incommensurate charge peaks are weak and unobservable in zero field in elastic neutron-scattering measurements, respectively, the normal-state value of Rho_ab_ at low temperatures markedly increases with increasing field up to 27 T. For La_2-x_Ba_x_CuO_4_ with x=0.11 and Zn-substituted La_2-x_Sr_x_Cu_1-y_Zn_y_O_4_ with x=0.115 and y=0.02 where the charge stripe order is fairly stabilized in zero field, on the other hand, the increase in Rho_ab_ with increasing field is negligibly small. In conclusion, when the charge-spin stripe order is not fully stable in zero field, magnetic field operates to stabilize the charge-spin stripe order. The value of Rho_ab_ increases with increasing field depending on the stability of the charge stripe order.Comment: 4 pages, 2 figures, Proceedings of Yamada Conference LX on Research in High Magnetic Fields (RHMF2006) (Satellite of ICM2006