Influence of shock-bubble and bubble-bubble interactions on the collapse of a cluster of bubbles

The present work is concerned with direct numerical simulations for the shock-bubble and bubble-bubble interactions using the improved ghost fluid method in which the Riemann solutions are utilized to diminish numerical oscillations near interfaces. The influence of bubble size and bubble-bubble distance on the collapse of in-line two bubbles and in-line three bubbles are investigated to understand the conditions under which the bubble-bubble interactions accelerate or decelerate the bubble collapse. It is shown that when the in-line bubbles collapse by the incident shock wave, the collapse of the downstream bubble can be accelerated by the shock waves due to the collapse of upstream bubbles, while the collapse of the upstream bubbles is decelerated by the expansion wave cased by the reflection of the incident shock wave at the surface of the downstream bubbles. Also, there exists the bubble-bubble distance in which the collapse of the downstream bubble is most accelerated. When the downstream bubble is smaller than the upstream bubble, the downstream bubble collapses more violently than the single bubble at any distance between the bubbles. The phase of the downstream bubble at the impact of the shock waves generated from the upstream bubbles is important in determining the acceleration of the collapse of the downstream bubble. It is also shown that the pressure increase in liquid near the axis of symmetry around the downstream bubble increases with the increase of number of bubbles and with the decrease of the bubble-bubble distance because the pressure increase in liquid is caused by the superposition of the shock waves generated from all bubbles.http://deepblue.lib.umich.edu/bitstream/2027.42/84251/1/CAV2009-final53.pd

Past and future of a century old Citrus tristeza virus collection: a California citrus germplasm tale.

Citrus tristeza virus (CTV) isolates collected from citrus germplasm, dooryard and field trees in California from 1914 have been maintained in planta under quarantine in the Citrus Clonal Protection Program (CCPP), Riverside, California. This collection, therefore, represents populations of CTV isolates obtained over time and space in California. To determine CTV genetic diversity in this context, genotypes of CTV isolates from the CCPP collection were characterized using multiple molecular markers (MMM). Genotypes T30, VT, and T36 were found at high frequencies with T30 and T30+VT genotypes being the most abundant. The MMM analysis did not identify T3 and B165/T68 genotypes; however, biological and phylogenetic analysis suggested some relationships of CCPP CTV isolates with these two genotypes. Phylogenetic analysis of the CTV coat protein (CP) gene sequences classified the tested isolates into seven distinct clades. Five clades were in association with the standard CTV genotypes T30, T36, T3, VT, and B165/T68. The remaining two identified clades were not related to any standard CTV genotypes. Spatiotemporal analysis indicated a trend of reduced genotype and phylogenetic diversity as well as virulence from southern California (SC) at early (1907-1957) in comparison to that of central California (CC) isolates collected from later (1957-2009) time periods. CTV biological characterization also indicated a reduced number and less virulent stem pitting (SP) CTV isolates compared to seedling yellows isolates introduced to California. This data provides a historical insight of the introduction, movement, and genetic diversity of CTV in California and provides genetic and biological information useful for CTV quarantine, eradication, and disease management strategies such as CTV-SP cross protection

Growth and Magnetic Properties of MnO₂-δ Nanowire Microspheres

We report the synthesis of MnO2-delta microspheres using hydrothermal and conventional chemical reaction methods. The microspheres of MnO2-delta consist of nanowires having a diameter of 20-50 nm and a length of 2-8 µm. The value of oxygen vacancy delta estimated from x-ray photoelectron spectrum is 0.3. The magnetization versus temperature curve indicates a magnetic transition at about 13 K. It is found that a parasitic ferromagnetic component is imposed on the antiferromagnetic structure of MnO2-delta, which might result from distortion of the lattice structure due to oxygen vacancies. The magnetic transition temperature TN is about 10 K lower than that of the bulk MnO2 single crystal

Relationship between production of acute-phase proteins and strength of inflammatory stimulation in rats

The relationship between intensity of inflammatory stimulation and production of α2-macroglobulin (α2M) and α1-acid glycoprotein (AAG) in rats was investigated. Sprague-Dawley rats were injected with turpentine oil at doses of 0.05, 0.2 or 0.4 mL/rat. Serum levels of α2M, interleukin (IL)-6 and cytokine-induced neutrophil chemoattractant-1 (CINC-1) were measured by enzyme-linked immunosorbent assay, and AAG was measured by single radial immunodiffusion. Peak serum levels of α2M and AAG in rats injected at 0.05 mL/rat were significantly lower than those at 0.2 or 0.4 mL/rat. However, no significant differences were observed for peak serum levels of these acute-phase proteins between 0.2 and 0.4 mL/rat. Furthermore, peak serum levels of IL-6 and CINC-1 in rats injected at 0.05 mL/rat were significantly lower than those at 0.2 or 0.4 mL/rat. Thus, the production of these acute-phase proteins has upper limits, even under increased strength of inflammatory stimulation in rats injected with turpentine oil

Observation of Novel Disordered Rhombohedral R₂Fe₁₇ (R=Rare Earth) Based Compounds

A recent study of (SmGd)Fe 14Si3 showed an anomalous x-ray diffraction pattern [P. C. Ezekwenna, G. K. Marasinghe, J.-H. Nam, W. J. James, W. B. Yelon, M. Ellouze, and Ph. I\u27Héritier, J. Appl. Phys. 87, 6716 (2000)]. Although all observed peaks could be indexed to the rhombohedral 2:17 phase (R-3m) many lines were strongly reduced in intensity. Subsequently, the same phenomenon was seen in neutron diffraction patterns from Nd2-xDysFe17-ySiy alloys and conventional refinement using the rhombohedral phase left significant residuals. Fourier mapping revealed additional density along the c-axis chains of Fe dumbbells and rare earth atoms. The perfect a-b-c stacking of the CaCu5 layers with regular 1/3 replacement of the rare earth atoms by Fe dumbbells appears to be broken. Detailed analysis shows that excess Fe dumbbells are incorporated into the structure and some reverse substitution is seen. In addition, the weak intensities are associated with a near equivalence of the 9d and 18h Fe sites, as in the parent CaCu5 phase. The relationship of this new structure to the other CaCu5 derived phases is described. The high Fe concentration creates the possibility of high TC and higher remanence than in the ordered 2:17 compounds

Structural, Magnetic, and Transport Properties of Zr-substituted La₀.₇ Sr₀.₃ Mn O₃

Zr-substituted perovskites La0.7Sr0.3 Mn1-x Zrx O3 with 0 ≤ x ≤ 0.20 were investigated by neutron diffraction (ND), magnetization, electric resistivity, and magnetoresistance measurements. ND refinements reveal that substituted Zr4+ goes only to the Mn site. Because of its large size, this leads to a Zr-solubility limit at x ≤ 0.10. The x ≤ 0.10 samples exhibit a rhombohedral structure (R3c) from 10 K to room temperature. For the x ≤ 0.10 samples, the cell parameters a and c, and volume increase continuously with increasing Zr content. In addition, the structural distortion of the Mn O6 octahedra increases with increasing Zr content. Zr-substituted La0.7 Sr0.3 Mn1-x Zrx O3 exhibits metallic behavior at low temperature. The field dependent resistivity suggests that electron-electron scattering is dominant and a two-magnon scattering process emerges with increasing temperature. The contribution from the two-magnon scattering in resistivity becomes larger with increasing Zr content. A maximum magnetoresistance (MRmax) of 35% is obtained for the x=0.03 sample at H=5 T. The MRmax shifts to a higher temperature region upon application of an external magnetic field

Indole Pulse Signalling Regulates the Cytoplasmic pH of E. coli in a Memory-Like Manner.

Bacterial cells are critically dependent upon pH regulation. Here we demonstrate that indole plays a critical role in the regulation of the cytoplasmic pH of Escherichia coli. Indole is an aromatic molecule with diverse signalling roles. Two modes of indole signalling have been described: persistent and pulse signalling. The latter is illustrated by the brief but intense elevation of intracellular indole during stationary phase entry. We show that under conditions permitting indole production, cells maintain their cytoplasmic pH at 7.2. In contrast, under conditions where no indole is produced, the cytoplasmic pH is near 7.8. We demonstrate that pH regulation results from pulse, rather than persistent, indole signalling. Furthermore, we illustrate that the relevant property of indole in this context is its ability to conduct protons across the cytoplasmic membrane. Additionally, we show that the effect of the indole pulse that occurs normally during stationary phase entry in rich medium remains as a "memory" to maintain the cytoplasmic pH until entry into the next stationary phase. The indole-mediated reduction in cytoplasmic pH may explain why indole provides E. coli with a degree of protection against stresses, including some bactericidal antibiotics.The Leverhulme Trus

Structural, Electronic, and Magnetic Properties of LaNi₅₋ₓTₓ (T = Fe, Mn) Compounds

Structures and magnetic properties of the LaNi5-xFex and LaNi5-xMnx compounds have been investigated using neutron diffraction and first-principles tight-binding-linear-muffin-tin-orbital methods. Both neutron diffraction refinement data and total energy calculations show that the Fe and Mn atoms preferentially occupy the 3g sites in the hexagonal CaCu5-type structure. The calculated magnetic moments of Fe and Ni atoms are of 2.4-2.5μB and 0.2-0.5μB in LaNi5-xFex, respectively. The magnetic structure exhibits more localized moments at Fe atoms in LaNi5-xFex when x ≤ 1.0. Electronic structure calculations indicate that s-conduction electron spin polarization from the Ni or La atoms strongly interacts with Fe(Mn) d-spin moments in LaNi5-xFe(Mn)x (x ≠ 0) compounds, which gives rise to a very large valence transferred hyperfine field on the Ni or La sites. This s-d hybridization may lead to an interaction among magnetic clusters in these kinds of materials and may cause a spin freezing effect at low temperature when the Fe(Mn) content is very low in LaNi5-xFe(Mn)x. Mn atoms show magnetic moments of 3.0μB per atom due to a large exchange splitting in LaNi5-xMnx (x ≠ 0). LaNi4Mn is found to be ferrimagnetic, whereas antiferromagnetic exchange coupling between the Mn atoms is preferred for LaNi3Mn2. Both ferrimagnetic and ferromagnetic exchange interactions between Mn atoms are found in the LaNi2Mn3 compounds. The calculated results are in good agreement with the experimental neutron data

Neutron and Magnetic Studies of La₀.₇Sr₀.₃Mn₁₋ₓCrₓO₃(x ≤ 0.7): A Homogeneous Charge-Ordered System

Structural and magnetic properties of La0.7Sr0.3Mn1-xCrxO3 (0 \u3c x ≤ 0.7) have been studied in order to determine the effect of substitution of Cr3+ for Mn3+. The data consist of neutron and x-ray powder-diffraction and magnetization measurements. We previously suggested these systems transition from ferromagnetic to antiferromagnetic ordering with the intermediate concentrations containing coexisting ferromagnetic and antiferromagnetic domains. Upon further detailed examination, we find that the neutron data can be fit using a single homogeneous long-range magnetically ordered state and compositionally dependent charge ordering. The magnetic structures are controlled by the competition between Mn-Mn, Mn-Cr, and Cr-Cr interactions (double exchange and superexchange). The metal to semimetal and semimetal to insulator transitions can be quantitatively described as due to the localization effect of superexchange. The presence of charge ordered states in the insulating region arises from the favorable energetics of Mn4+-O-Cr3+ superexchange bonds relative to Mn3+-O-Cr3+ bonds