We have developed a new method to investigate the relaxation time of the dipole moment in polarization clusters in BaTiO3. Time correlation of speckle intensities was measured by the use of a double ...pulsed soft x-ray laser. The evolution of the relaxation time of the dipole moment near the Curie temperature (T(C)) was investigated. The maximum relaxation time (approximately 90 ps) is shown to appear at a temperature of 4.5 K above the T(C), being coincident with the one where the maximum polarization takes place. This method is widely applicable to any other critical decay processes at phase transitions.
We systematically investigated perpendicular magnetic anisotropy (PMA) in bilayers comprising ultrathin full-Heusler Co2FeSi (CFS) alloy and MgO as an insulator. The MgO layer was fabricated using ...two different sputtering techniques: reactive sputtering and radio-frequency sputtering. The characteristics of the layers fabricated using the different methods were compared. Irrespective of the MgO fabrication technique, the CFS/MgO bilayers exhibited PMA when the CFS surface was exposed to oxygen, which resulted in additional Fe–O bonds at the interface. Additionally, we characterized PMA in the bilayers while varying the substrate temperature TS for CFS sputtering. CFS samples that were 0.6-nm thick exhibited PMA when they were formed at TS as high as 300°C. The bilayer formed at 350°C exhibited in-plane magnetic anisotropy. Quantitative analysis of the magnetic anisotropy energy density revealed that the dominant magnetic anisotropy contribution in PMA differed between the bilayers formed at 300°C and 350°C. We expect these findings to be useful in the further development of high spin-polarized ferromagnetic electrodes containing PMA for next-generation spintronics devices.
In this article we investigate the stability of quantized yrast states in a mixture of two distinguishable equal mass bosonic atoms confined in a ring. We focus in the study of energetic stability ...since the Bloch analysis and the Bogoliubov theory establishes that only energetically stable quantized yrast states are capable of sustain a persistent current. In the framework of the Bogoliubov theory we study the stability in two different cases chosen by physical considerations. In one case we analyze how the inter and intraspecies interaction strengths affect the stability of a selected quantized yrast state specified by the angular momentum per particle and the population imbalance. In the other case, for a fixed dynamics specified by given values of interaction strengths, we determine the stability of quantized yrast states as function of the angular momentum per particle and the population imbalance. We also examined the stability of the mixture in the rarefied limit and we found a critical value of the population imbalance which gives the size of the window of energetic stability and a critical value of angular momentum per particle which is an upper bound of the possible values of angular momentum per particle carried by energetically stable quantized yrast states.
AbstractPumice sand particles have a vesicular nature, making them light and crushable. Previous research showed that the in situ relative density of pumice deposits cannot be estimated from ...conventional cone penetration testing. Because of this, a need exsits for more study of the geotechnical properties of this material. First, to distinguish compression behavior of loose and dense sand, K0 compression tests were performed on pumice specimens at various strain rates, from 0.33% to 1,000%/min, until a final compression of approximately 33% of the original specimen length was achieved. Second, after compression, the maximum displacement was held constant for a period of time during which the relaxation of the axial stress was monitored. After unloading, the particle-size distribution was measured to confirm particle crushing. From these results, the magnitude of stress relaxation of loose sand was found to be slightly larger than that of dense sand. On the other hand, dense sand particles exhibited more crushing during loading and less tendency for stress relaxation and particle rearrangement when the axial deformation is held fixed.
The removal of the protozoan parasite, Cryptosporidium parvum, from wastewaters is becoming of increasing importance in the UK, especially since contamination of raw waters by sewage effluents has ...been implicated in major waterborne outbreaks of cryptosporidiosis in recent years. Compared to conventional wastewater-treatment processes, constructed wetlands have demonstrated favourable removal rates for Cryptosporidium oocysts. The removal mechanisms, however, remain unknown. Predation by free-living ciliated protozoa, which are commonly found in constructed wetlands, was investigated as a possible mechanism for oocyst removal. In laboratory feeding experiments, ciliates (Euplotes patella, Stylonychia mytilus, Paramecium caudatum and an unidentified wetland ciliate species), were exposed to doses ranging from 10 to 10(6) oocysts/ml for between 5 and 60 minutes. Ciliate predatory activities were assessed by enumerating fluorescently labelled ingested oocysts using epifluorescence microscopy. Oocysts were found to be ingested by all species investigated. Paramecium demonstrated the highest mean ingestion rates (up to 170 oocysts/hr) followed by Stylonychia (up to 60 oocysts/hour). Euplotes and the wetland ciliate had lower mean grazing rates (4 and 10 oocysts/hr respectively). These results indicate that protozoan predation may be an important factor in the removal of Cryptosporidium oocysts from wastewaters in constructed wetlands.
The purpose of this study is to evaluate the effect of C18 and C20 long chain fatty acids on tight junction permeability in a model of intestinal epithelium. Methods: Confluent Caco-2 cells on porous ...filters with double chamber system were used to measure fluorescein sulfonic acid (FS) permeability and transepithelial electrical resistance (TEER). Lactate dehydrogenase release and ultrastructure were evaluated. Effect of 200 μM eicosapentaenoic acid (EPA, C20:5 n-3), arachidonic acid (AA, C20: 4 n-6), α -linoleic acid (ALA, C18: 3 n-3), linoleic acid (LA, C18: 2 n-6), or oleic acid (OA, C18: 1 n-9) enrichment in the culture medium during 24 hours were compared. The effect of the cyclooxygenase inhibitor, indomethacin, lipoxygenase inhibitors, NDGA or AA861, and antioxidant, BHT, was evaluated as a mechanism to change tight junction permeability. Results: Caco-2 cells formed polarized columner epithelial cells with densely packed microvilli and well developed junctional complexes. Addition of EPA enhanced FS permeability to 3.0±1.6-fold and lowered TEER to 0.59±1.2-fold vs. control with concentration dependency without cell injury (P<0.01–0.05). OA, AA or LA did not change, but ALA enhanced tight junction permeability. Indomethacin and AA861 normalized the changes mediated by EPA.Conclusions: EPA affects tight junction permeability in intestinal monolayer cells specifically and concentration dependently via cyclooxygenase and lipoxygenase products.
In order to search for Pb-free relaxor substances and to define relaxor behaviour, a theoretical aspect is presented from not only microscopic but also phenomenological viewpoint. In order-disorder ...type mixed crystals, the microscopic approach is attempted under conditions similar to those for relaxor perovskite-type oxides. Basing on the theory for the precursor to glass state, two kinds of technique of X-ray diffuse scattering (static properties) and quadrupole perturbed nuclear magnetic resonance (NMR-NQR) (dynamic properties) are discussed in ferroelectric (FE) -- antiferroelectric (AFE) mixed crystals of Rb
1−x
(NH
4
)
x
H
2
PO
4
. After investigating both boundary regions between FE and glass (G) phases, and between AFE and G phases, relaxor-like behaviours as a large dispersion in dielectric constants are found in the AFE-G phase boundary region where the gradual growth of wave number to make the energy minimum and a discontinuous broad NMR-NQR spectrum appear in quite different forms from those of the FE-G phase boundary region. On the other hand, in perovskite-oxides, the conditions for relaxor appearance are discussed within the phenomenological theory by comparing with the microscopic analysis in hydrogen-bonded systems.
Based on a theoretical analysis, the optimum path and the diffusivity are proposed for the proton hopping in perovskite-type oxides (ex. Sc-doped SrTiO
3), and the possible electric conduction paths ...and the diffusion constants are explained by comparing with some kinds of experimental data. Furthermore, numerical results suggest the possibility of a new conduction mechanism; the proton jumping process along the OO bond at high-temperatures changes to proton tunneling process, leading to an almost
T-independent conductivity at low temperatures. Within this theoretical approach in perovskite-oxides, the high-conduction mechanism with low proton concentration is discussed with reference to the results by MD simulation and the neutron diffraction, including the prediction on H(D)-isotope effect and the pressure dependence of the proton conductivity.
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