Magnetic Field Amplification Associated with the Richtmyer-Meshkov Instability

The amplification of a magnetic field due to the Richtmyer-Meshkov instability (RMI) is investigated by two-dimensional MHD simulations. Single-mode analysis is adopted to reveal definite relation between the nonlinear evolution of RMI and the field enhancement. It is found that an ambient magnetic field is stretched by fluid motions associated with the RMI, and the strength is amplified significantly by more than two orders of magnitude. The saturation level of the field is determined by a balance between the amplified magnetic pressure and the thermal pressure after shock passage. This effective amplification can be achieved in a wide range of the conditions for the RMI such as the Mach number of an incident shock and the density ratio at a contact discontinuity. The results suggest that the RMI could be a robust mechanism of the amplification of interstellar magnetic fields and cause the origin of localized strong fields observed at the shock of supernova remnants.Comment: 16 pages, 9 figures, accepted for publication in Ap

Colonization by Clostridium difficile of neonates in a hospital, and infants and children in three day-care facilities of Kanazawa, Japan

The intestinal-carriage rates of i>Clostridium difficile in neonates hospitalized in the University Hospital’s Center for Perinatal and Reproductive Health and in infants and children enrolled in two day-nurseries and a kindergarten were examined. Swab samples from the floors of these facilities were also analyzed to determine the extent of environmental contamination by this organism. C. difficile was found in the stool of only one of 40 neonates during the normal 1-week stay in the hospital after delivery. The isolate from the neonate was identical to that of her mother, as determined by PCR ribotyping, pulsed-field gel electrophoresis analysis, and toxin gene type, suggesting that the C. difficile-positive neonate acquired the organism from her mother rather than from the environment. By contrast, 47 (48.0%) of the 98 infants and children, comprising 50 enrolled in two daynurseries who were ≤3 years old and 48 enrolled in a kindergarten who were 2–5 years old, carried C. difficile. The carriage rate in infants under 2 years of age was much higher (84.4%) than in children 2 years old and older (30.3%). When analyzed according to age group, the carriage rates were 100, 75.0, 45.5, 24.0, 38.5, and 23.5% in infants and children 0, 1, 2, 3, 4, and 5 years old, respectively. The observation that several children were colonized with the same type of C. difficile strain in each day-care facility, and that the floors of day-nursery A and kindergarten C were contaminated with C. difficile strains identical to those colonizing the intestines of children enrolled in those facilities suggests that cross-infection of C. difficile among children occurs through C. difficile-carrying children or their contaminated environments. [Int Microbiol 2005; 8(1):43-48

3d puzzle in cube pattern for anisotropic/isotropic mechanical control of structure fabricated bymetal additivemanufacturing

Metal additive manufacturing is a powerful tool for providing the desired functional performance through a three-dimensional (3D) structural design. Among the material functions, anisotropic mechanical properties are indispensable for enabling the capabilities of structural materials for living tissues. For biomedical materials to replace bone function, it is necessary to provide an anisotropic mechanical property that mimics that of bones. For desired control of the mechanical performance of the materials, we propose a novel 3D puzzle structure with cube-shaped parts comprising 27 (3 × 3 × 3) unit compartments. We designed and fabricated a Co–Cr–Mo composite structure through spatial control of the positional arrangement of powder/solid parts using the laser powder bed fusion (L-PBF) method. The mechanical function of the fabricated structure can be predicted using the rule of mixtures based on the arrangement pattern of each part. The solid parts in the cubic structure were obtained by melting and solidifying the metal powder with a laser, while the powder parts were obtained through the remaining nonmelted powders inside the structure. This is the first report to achieve an innovative material design that can provide an anisotropic Young’s modulus by arranging the powder and solid parts using additive manufacturing technology.Ikeo N., Fukuda H., Matsugaki A., et al. 3d puzzle in cube pattern for anisotropic/isotropic mechanical control of structure fabricated bymetal additivemanufacturing. Crystals, 11, 8, 959. https://doi.org/10.3390/cryst11080959

Diffusionless isothermal omega transformation in titanium alloys driven by quenched-in compositional fluctuations

In titanium alloys, the ω(hexagonal)-phase transformation has been categorized as either a diffusion-mediated isothermal transformation or an athermal transformation that occurs spontaneously via a diffusionless mechanism. Here we report a diffusionless isothermal ω transformation that can occur even above the ω transformation temperature. In body-centered cubic β-titanium alloyed with β-stabilizing elements, there are locally unstable regions having fewer β-stabilizing elements owing to quenched-in compositional fluctuations that are inevitably present in thermal equilibrium. In these locally unstable regions, diffusionless isothermal ω transformation occurs even when the entire β region is stable on average so that athermal ω transformation cannot occur. This anomalous, localized transformation originates from the fluctuation-driven localized softening of 2/3[111]β longitudinal phonon, which cannot be suppressed by the stabilization of β phase on average. In the diffusionless isothermal and athermal ω transformations, the transformation rate is dominated by two activation processes: a dynamical collapse of {111}β pairs, caused by the phonon softening, and a nucleation process. In the diffusionless isothermal transformation, the ω-phase nucleation, resulting from the localized phonon softening, requires relatively high activation energy owing to the coherent β/ω interface. Thus, the transformation occurs at slower rates than the athermal transformation, which occurs by the widely spread phonon softening. Consequently, the nucleation probability reflecting the β/ω interface energy is the rate-determining process in the diffusionless ω transformations.Tane M., Nishiyama H., Umeda A., et al. Diffusionless isothermal omega transformation in titanium alloys driven by quenched-in compositional fluctuations. Physical Review Materials 3, 043604 (2019); https://doi.org/10.1103/PhysRevMaterials.3.043604

An Arabidopsis SBP-domain fragment with a disrupted C-terminal zinc-binding site retains its tertiary structure

AbstractSQUAMOSA promoter-binding proteins (SBPs) form a major family of plant-specific transcription factors, mainly related to flower development. SBPs share a highly conserved DNA-binding domain of ∼80 amino acids (SBP domain), which contains two non-interleaved zinc-binding sites formed by eight conserved Cys or His residues. In the present study, an Arabidopsis SPL12 SBP-domain fragment that lacks a Cys residue involved in the C-terminal zinc-binding pocket was found to retain a folded structure, even though only a single Zn2+ ion binds to the fragment. Solution structure of this fragment determined by NMR is very similar to the previously determined structures of the full SBP domains of Arabidopsis SPL4 and SPL7. Considering the previous observations that chelating all the Zn2+ ions of SBPs resulted in the complete unfolding of the structure and that a mutation of the Cys residue equivalent to that described above impaired the DNA-binding activity, we propose that the Zn2+ ion at the N-terminal site is necessary to maintain the overall tertiary structure, while the Zn2+ ion at the C-terminal site is necessary for the DNA binding, mainly by guiding the basic C-terminal loop to correctly fit into the DNA groove

Outstanding in vivo mechanical integrity of additively manufactured spinal cages with a novel “honeycomb tree structure” design via guiding bone matrix orientation

BACKGROUND CONTEXT: Therapeutic devices for spinal disorders, such as spinal fusion cages, must be able to facilitate the maintenance and rapid recovery of spinal function. Therefore, it would be advantageous that future spinal fusion cages facilitate rapid recovery of spinal function without secondary surgery to harvest autologous bone. PURPOSE: This study investigated a novel spinal cage configuration that achieves in vivo mechanical integrity as a devise/bone complex by inducing bone that mimicked the sound trabecular bone, hierarchically and anisotropically structured trabeculae strengthened with a preferentially oriented extracellular matrix. STUDY DESIGN/SETTINGS: In vivo animal study. METHODS: A cage possessing an anisotropic through-pore with a grooved substrate, that we termed “honeycomb tree structure,” was designed for guiding bone matrix orientation; it was manufactured using a laser beam powder bed fusion method through an additive manufacturing processes. The newly designed cages were implanted into sheep vertebral bodies for 8 and 16 weeks. An autologous bone was not installed in the newly designed cage. A pull-out test was performed to evaluate the mechanical integrity of the cage/bone interface. Additionally, the preferential orientation of bone matrix consisting of collagen and apatite was determined. RESULTS: The cage/host bone interface strength assessed by the maximum pull-out load for the novel cage without an autologous bone graft (3360±411 N) was significantly higher than that for the conventional cage using autologous bone (903±188 N) after only 8 weeks post-implantation. CONCLUSIONS: These results highlight the potential of this novel cage to achieve functional fusion between the cage and host bone. Our study provides insight into the design of highly functional spinal devices based on the anisotropic nature of bone. CLINICAL SIGNIFICANCE: The sheep spine is similar to the human spine in its stress condition and trabecular bone architecture and is widely recognized as a useful model for the human spine. The present design may be useful as a new spinal device for humans.Ishimoto T., Kobayashi Y., Takahata M., et al. Outstanding in vivo mechanical integrity of additively manufactured spinal cages with a novel “honeycomb tree structure” design via guiding bone matrix orientation. Spine Journal, 22, 10, 1742. https://doi.org/10.1016/j.spinee.2022.05.006