B2 Clusters Research Articles

Molecular Epidemiological Investigation of a Nosocomial Outbreak of Human Metapneumovirus Infection in a Pediatric Hemato-Oncology Patient Population

We report the first nosocomial outbreak of human metapneumovirus (hMPV) infection in a pediatric patient population. Among 15 pediatric hMPV infections from March to May 2007, there was a nosocomial outbreak involving two patients sharing a room in a hemato-oncology ward with a patient with a community-acquired case of hMPV infection. The estimated incubation period was 7 to 9 days for a symptomatic nosocomial case. Sequencing of fusion genes of 15 isolates revealed two clusters belonging to subgroup A2 and one cluster belonging to subgroup B2. Three isolates from the outbreak had sequences identical to those of samples in the A2 cluster. There was also a separate nosocomial case represented by the B2 cluster.

Atomic structure of soft magnetic Fe-Si alloys with induced magnetic anisotropy

The atomic structure of iron-based alloys with 5–6 at. % Si has been studied using X-ray diffraction. It has been shown that the average size of B2-ordered clusters existing in these alloys depends on the sample prehistory (on the preparation method). Thermomagnetic and thermomechanical treatments were used to produce states with a desired type of magnetic structure. The largest size of B2 clusters was obtained in the direction of the magnetic anisotropy after it was induced. Based on the results of simulation of diffraction patterns, the microstructure of clusters was interpreted as consisting of adjacent pairs of B2 cells surrounded by distorted cells of the bcc matrix.

B2 and D0 3 clusters in soft magnetic single crystal Fe 1−xSi x alloys with induced magnetic anisotropy

The atomic structure of α-Fe 1− x Si x single crystals with x = 0.05 , 0.06, and 0.08 was studied by means of X-ray diffraction to clarify the origin of the magnetic anisotropy induced under thermomagnetic or thermomechanical treatment. The B2-type short-range order is observed only at x = 0.05 and 0.06. B2 clusters, about 8 Å in size, are extended in the direction of induced magnetic anisotropy by ∼2 Å more than in a direction transverse to it. When the sequential junction of B2 unit cells—two or more in number—is realized along the easy magnetization axes 〈1 0 0〉, the B2 clusters are inevitably anisotropic. The probability of the orientation of B2 clusters along any of the axes 〈1 0 0〉 is the same. The appeared preferable orientation of B2 clusters upon annealing in a dc saturating magnetic field or under stress loading has emerged via the Si-atom diffusion. After cooling, this anisotropic B2-cluster distribution becomes “frozen” and is the origin of the appearance and stability of the uniaxial anisotropy of magnetic properties. In Fe 0.92Si 0.08, the B2 clusters coexist with D0 3 clusters, the latter being isotropic. With increasing x, the increase in a D0 3-phase amount progressively suppresses the magnetic anisotropy caused by anisotropic distribution of B2 clusters, and, to be exact, completely, at x ∼ 0.14 .

Fluoroquinolone-resistantEscherichia coli, Indonesia

In a recent, population-based survey of 3,996 persons in Indonesia, fluoroquinolone (FQ)-resistant Escherichia coli was prevalent in the fecal flora of 6% of patients at hospital admission and 23% of patients at discharge, but not among healthy relatives or patients visiting primary healthcare centers (2%). Molecular typing showed extensive genetic diversity with only limited clonality among isolates. This finding suggests that independent selection of resistant mutants occurs frequently. FQ-resistant isolates exhibited a higher rate of spontaneous mutation, but sparser virulence profiles, than FQ-susceptible isolates from the same population. The resistant isolates belonged predominantly to phylogenetic groups A (57%) and B1 (22%) but also to the moderately virulent group D (20%). Hypervirulent strains from the B2 cluster were underrepresented (1%). Because FQ-resistant E. coli can cause disease, especially nosocomial infections in immunocompromised patients, spread of such strains must be stopped.

Expression and distribution of transcription factor CCAAT/enhancer-binding protein in the central nervous system of Lymnaea stagnalis

The transcription factor, CCAAT/enhancer-binding protein (C/EBP), is involved in important physiological processes, such as cellular proliferation and differentiation, homeostasis, and higher-order functions of the brain. In the present study, we investigated the distribution of mRNA and protein of C/EBP in the central nervous system of the pond snail, Lymnaea stagnalis, by in situ hybridization and immunohistochemistry. Specificity of the anti-mammalian C/EBP antibody against Lymnaea C/EBP (LymC/EBP) was confirmed by combination of sodium dodecyl sulfate polyacrylamide gel electrophoresis or isoelectric focusing and immunoblotting. Cells positive for in situ hybridization were immunoreactive for LymC/EBP in all 11 ganglia. The motoneurons (B1, B2, B4, and B4 clusters) in the buccal ganglia and interneurons (cerebral giant cell, CGC) in the cerebral ganglia were positive for in situ hybridization and were immunopositive. In the pedal ganglion, the right pedal dorsal 1 (RPeD1), pedal A, and pedal C clusters exhibited positive signals of in situ hybridization and immunohistochemistry for LymC/EBP. CGC and RPeD1 are key neurons for associative learning. In addition, the neuropeptidergic cells in the cerebral, pleural, parietal, and visceral ganglia were positive for in situ hybridization and immunoreactive. Interestingly, although the cytoplasm of almost all immunopositive cells was stained, some neuropeptidergic cells located in the light parietal and visceral ganglia exhibited immunoreactivity in nuclei. Our results suggest that LymC/EBP is involved in learning and memory and in the expression and/or secretion of neuropeptides in Lymnaea.

Spectroscopic Studies of the Herbig-Haro Objects Hh84 and Hh85

Spectroscopic studies have been made of the two Herbig-Haro objects HH84 and HH85. Isocontours of the [SII] emission lines, the radial velocities, and the relative line intensities and electron densities are given for the A, B, C, E clusters of HH84 and the A, B1, and B2 clusters of HH85. Comparisons with earlier results are made. Significant variations in the radial velocities and line widths are observed within the confines of HH84. It is concluded that HH84 may actually be a shock wave at the termination of a collimated outflow, but it is still not known whether this flow is coupled to HH83. HH85 is definitely a part of the HH34 giant outflow.

Prototype calculations of B2 miscibility gaps in ternary b.c.c. systems with strong ordering tendencies

Prototype calculations in ternary ordering systems based on the b.c.c. lattice have been carried out with the Cluster Variation Method (CVM) in the irregular tetrahedron approximation including tetrahedron interactions. The systems under investigations were characterized by strong ordering tendencies (i.e. with large, negative first neighbour interactions in all binary sub-systems) which resulted in the opening of a miscibility gap inside the B2 single-phase field. This miscibility gap is shown to be produced by frustration of the B2 cluster by a calculation using a hypothetical system with identical first neighbour interactions in the three binary sub-systems. This phase diagram presents as a key feature a central three-phase miscibility gap, which transforms into an ordinary two-phase miscibility gap involving two B2 phases after the symmetry of the interactions is broken. The results are discussed in connection with the experimental Fe–Ti–Rh phase diagram.

Theoretical study of the structural, vibrational, and topologic properties of the charge distribution of the molecular complexes between thiophene and Brönsted acid sites of zeolites

AbstractThe main interaction between thiophene and zeolites leads to the formation of a hydrogen bond between the S atom of thiophene and the OH group of zeolites, giving 1:1 stable molecular complexes. The present work reports a theoretical study about the structural, vibrational, and topologic properties of the charge distribution of the molecular complexes between thiophene and a series of Brönsted acid sites of zeolites, modeled as the H3SiOHAlH3(B1), (OH)3Si(OH)Al(OH)3(B1OH), and H3Si(OH)Al(OH)2OSiH3(B2) clusters. The studied properties were calculated at a Hartree–Fock level with the standard 6‐31+G(d,p) basis set. Additionally, electron correlation effects for geometric and vibrational properties were evaluated at second‐order Møller–Plesset (MP2) and BLYP for B1–thiophene complex, whereas the BLYP technique was employed for the complexes of thiophene with B1OH and B2 clusters. Symmetry restriction was considered for structure calculations, beingC2vfor thiophene,Csfor zeolite clusters, andCslinear conformation for the complexes. It was found that these linear thiophene–zeolite complexes reproduce the tendencies in the experimental frequency shifts of the OH vibration mode from the adsorption of thiophene in ZSM5 zeolites. The topologic properties of the complexes give a pattern for the interaction of thiophene–zeolite. The results are compared with previous ones from silanol–thiophene calculations. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001

Tight-binding studies of the tendency for boron to cluster in c-Si. II. Interaction of dopants and defects in boron-doped Si

Clusters containing up to five boron atoms were considered as extended defects within a crystalline Si matrix. Tight-binding calculations suggest that a cluster containing two boron atoms occupying substitutional sites is stable, unlike any other small boron cluster that we studied. The formation energy increases when a third and fourth substitutional boron atom is added to the cluster. Estimates of the equilibrium concentration, using tight-binding-derived formation energies and formation entropies from the Stillinger–Weber model, indicate that B2 clusters become important when the boron doping level is ∼1018 cm−3, well below the solubility limit. In contrast, the formation energy of defect clusters involving an interstitial (BnI clusters, n=1–5, in their preferred charge states) decreases with increasing cluster size, down to 0.6 eV for B5I in a −5 charge state. None had formation energies that would lead to stable bound clusters. Several BnI clusters were found to be considerably more stable than isolated Si self-interstitials (by 1–2 eV), the BSBI cluster, assumed in some continuum modeling codes to be important, was not a particular interesting defect structure (a formation energy in the −2 charge state, EF−2, of 2.8 eV). There seemed to be little energetic penalty for creating clusters larger than about B5I, in good agreement with Sinno and Brown’s Stillinger–Weber studies of self-interstitial clusters in Si [Mater. Res. Soc. Symp. Proc. 378, 95 (1997)]. Some support was found for the suggestion of Pelaz et al. [Appl. Phys. Lett. 70, 2285 (1997)] that BI2 is a nucleation site for boron clustering. Boron clusters involving a boron interstitial were generally found to be less likely to form than analogous clusters involving a Si self-interstitial. B2 clusters involving vacancies are not energetically favored, confirming the known tendency for boron to diffuse via an interstitial mechanism rather than vacancies. These results suggest that boron clusters could serve as traps, which slow the diffusion of self-interstitials under conditions of interstitial supersaturation in highly doped silicon, consistent with experimental evidence.

Studies on the lattice position of boron in silicon†

Abstract From a compilation of known literature, the substitutional fraction of boron in silicon is depicted in a diagram as a function of implantation dose and annealing temperature. Samples implanted at 1 1016 B/cm2 and annealed at 900, 1000 and 1100°C for 1 hour each are examined by the (n, α) method and compared to the RBS signal of the host atoms in various directions. Our results indicate a gradual transition from completely random positions after 900°C anneal to substitutional sites after 1100°C anneal. The observation of random positions for B in Si, annealed at 900°C, disagrees with earlier experiments after application of (p, α) reactions. We ascribe the differences to proton irradiation induced boron diffusion in those former accelerator experiments by other authors. Our results for the samples annealed above 900°C indicate lattice positions for the interstitial boron fraction which were not yet discussed in the literature. After 1100°C anneal, nearly all B atoms are found on positions slightly (approx. 7%) displaced from substitutional sites. This may result from the formation of small B2 or B3 clusters during the cooling period of the thermal annealing procedure.