The impact of Allee effect on a predator–prey system with Holling type II functional response

In this paper, the Allee effect is incorporated into a predator–prey model with Holling type II functional response. Compared with the predator–prey model without Allee effect, we find that the Allee effect of prey species increases the extinction risk of both predators and prey. When the handling time of predators is relatively short and the Allee effect of prey species becomes strong, both predators and prey may become extinct. Moreover, it is shown that the model with Allee effect undergoes the Hopf bifurcation and heteroclinic bifurcation. The Allee effect of prey species can lead to unstable periodical oscillation. It is also found that the positive equilibrium of the model could change from stable to unstable, and then to stable when the strength of Allee effect or the handling time of predators increases continuously from zero, that is, the model admits stability switches as a parameter changes. When the Allee effect of prey species becomes strong, longer handling time of predators may stabilize the coexistent steady state.     

Study of various few-body systems using Gaussian expansion method (GEM)

We review our calculation method, Gaussian expansion method (GEM), to solve accurately the Schrödinger equations for bound, resonant and scattering states of few-body systems. Use is made of the Rayleigh-Ritz variational method for bound states, the complex-scaling method for resonant states and the Kohn-type variational principle to S-matrix for scattering states. GEM was proposed 30 years ago and has been applied to a variety of subjects in few-body (3- to 5-body) systems, such as 1) few-nucleon systems, 2) few-body structure of hypernuclei, 3) clustering structure of light nuclei and unstable nuclei, 4) exotic atoms/molecules, 5) cold atoms, 6) nuclear astrophysics and 7) structure of exotic hadrons. Showing examples in our published papers, we explain i) high accuracy of GEM calculations and its reason, ii) wide applicability of GEM to various few-body systems, iii) successful predictions by GEM calculations before measurements. The total bound-state wave function is expanded in terms of few-body Gaussian basis functions spanned over all the sets of rearrangement Jacobi coordinates. Gaussians with ranges in geometric progression work very well both for shortrange and long-range behavior of the few-body wave functions. Use of Gaussians with complex ranges gives much more accurate solution than in the case of real-range Gaussians, especially, when the wave function has many nodes (oscillations). These basis functions can well be applied to calculations using the complex-scaling method for resonances. For the few-body scattering states, the amplitude of the interaction region is expanded in terms of those few-body Gaussian basis functions.     

Spin chirality and electric polarization in multiferroic compounds (, Er)

Polarized neutron diffraction experiments have been performed on multiferroic materials RMn₂O₅ (R=Ho, Er) under electric fields in the ferroelectric commensurate (CM) and the low-temperature incommensurate (LT-ICM) phases, where the former has the highest electric polarization and the latter has reduced polarization. It is found that, after cooling in electric fields down to the CM phase, the magnetic chirality is proportional to the electric polarization. Also we confirmed that the magnetic chirality can be switched by the polarity of the electric polarization in both the CM and LT-ICM phases. These facts suggest an intimate coupling between the magnetic chirality and the electric polarization. However, upon the transition from the CM to LT-ICM phase, the reduction of the electric polarization is not accompanied by any reduction of the magnetic chirality, implying that the CM and LT-ICM phases contain different mechanisms of the magnetoelectric coupling.     

A fast spherical harmonics transform algorithm

The spectral method with discrete spherical harmonics transform plays an important role in many applications. In spite of its advantages, the spherical harmonics transform has a drawback of high computational complexity, which is determined by that of the associated Legendre transform, and the direct computation requires time of for cut-off frequency . In this paper, we propose a fast approximate algorithm for the associated Legendre transform. Our algorithm evaluates the transform by means of polynomial interpolation accelerated by the Fast Multipole Method (FMM). The divide-and-conquer approach with split Legendre functions gives computational complexity . Experimental results show that our algorithm is stable and is faster than the direct computation for .

     

Relaxation oscillations in combustion models of thermal self-ignition

Combustion processes are classified into three types depending upon the amount of fuel supply: two of them are the stationary states with either low or high temperatures and the other is the periodic state with relaxation oscillation type. We analyze the dependency of these processes on the amount of fuel supply by using the fast and slow dynamics approach.     

Performance of a Gyratory Square-Shaped Capacitive Radio Frequency Discharge Plasma Sputtering Source for Materials Processing

We proposed a gyratory square-shaped capacitive radio-frequency discharge plasma sputtering source for materials processing and functional film preparation, composed of magnet arrangements consisting of eight neodymium bar magnets of dimensions 30 mm × 5 mm × 3 mm. In order to evaluate its performance, two square-shaped magnetic arrangements were investigated: case (a) without iron shielding and case (b) with iron shielding of dimensions 5 mm × 3 mm × 1 mm. The magnetic field simulation is analyzed, while the plasma discharge characteristics and the film properties are measured. The film thickness and the resistivity profiles of case (b) are more uniform than their corresponding profiles in case (a). The lowest electrical resistivity of the film is 4.33 × 10^?8 Ω m at r = 30 mm for case (b), which is of the same order as the bulk resistivity of the copper. The roughnesses of the film thickness profile for cases (a) and (b) are ±24.4 and ±7.2%, respectively. Using atomic force microscopy analysis, the film surface for case (b) was observed to show an improved smooth surface with reduced needle-shaped grain size and a lower surface roughness than that of case (a). The surface roughness of the films is approximately 3.73 and 2.49 nm for case (a) and case (b), respectively. From the X-ray diffraction patterns, the film texture, the relative intensity ratios of the (111) peak to the (200) [I₍₁₁₁₎/ I₍₂₀₀₎] were found to be 13.76 and 4.08 for the cases (a) and (b), respectively.     

Modified DNA aptamer that binds the (R)-isomer of a thalidomide derivative with high enantioselectivity

A thalidomide-binding aptamer was produced by systematic evolution of ligands by exponential enrichment from a library of non-natural DNA in which thymidine had been replaced with a modified deoxyuridine bearing a cationic functional group via a hydrophobic methylene linker at the C5 position. The additional functional group in the modified DNA aptamer could improve stability against nucleases and increase the binding affinity to thalidomide. The selected aptamer could recognize thalidomide enantioselectively, although a racemic thalidomide-attached gel was used for the selection. Surface plasmon resonance and fluorescence titration studies revealed that the selected modified DNA aptamer and a truncated version bound with an (R)-thalidomide derivative with high enantioselectivity, but not with the (S)-form. The modified group in the DNA aptamer is indispensable for the interaction with thalidomide, as the corresponding natural type DNA bearing the same base sequence showed no binding affinity with (R)- nor (S)-thalidomide. Computational sequence analysis suggested that the selected apatamer (108 mer) could fold into a three-way junction structure; however, truncation of this aptamer (31 mer) revealed that the thalidomide-binding site is a hairpin-bulge region that is a component of one of the arms of the three-way junction structure. The Kd value of the truncated 31 mer aptamer for binding with the (R)-thalidomide derivative was 1.0 microM estimated from fluorescence titration study. The aptamer that can recognize a single enantiomer of thalidomide will be useful as a biochemical tool for the analysis and study of the biological action of thalidomide enantiomers.     

Fabrication of an Ultraviolet Light-Emitting Functional Probe of Sub-Micron Size by Photochemical Vapor Deposition

We report a new fabrication technique of a sub-micron sized probe consisting of functional material on the aperture of a metal coated optical fiber probe tip for near field optical microscopy. The selective fixation of sub-micron size functional material has been achieved by photochemical vapor deposition. Here, we demonstrate for the first time the selective fixation of zinc oxide, a wide gap semiconductor with ultraviolet emission ability, on such probe tips. Results reveal the efficient excitonic emission of 372 nm even at room temperature, which is characteristic of high quality zinc oxide.