Status of resource enhancement and sustainable aquaculture practices in Japan

Contrary to the rapid increase in the world aquaculture production, fish production in Japan has been decreasing slightly due to the decreasing trend in seafood consumption of Japanese. Aquaculture production is approximately 20% in terms of yield, and 30% in terms of market value, of the country s total fisheries production. In Japan, about 80 species are targeted for release for sea ranching and resource enhancement purposes. The local governments (prefectures) are the main driving force in resource enhancement programs. Chum salmon, Oncorhynchus keta, and scallop Mizuhopecten yessoensisis are examples of successful resource enhancement in Japan. Japanese flounder, Paralichthys olivaceus, and red seabream, Pagrus major, represent intensely released fish species in Japan, and around 10% of the total catch of those species are estimated as released fish. The low price of products and increasing costs of production, such as costs of fuel and fish meal, are the major pressing issues in coastal fisheries and aquaculture in Japan. For aquaculture, the guarantee of food safety, minimization of environmental impact, and management of natural stock populations are highly necessary in order to achieve the sustainability of the industry. For resource enhancement, budget constraint is the major issue, and possible impact on natural stocks caused by released fish should also be considered. The Government of Japan (GOJ) is implementing some measures to rectify unstable business practices of aquaculture and to improve production techniques in aquaculture. For resource enhancement, the GOJ encourages cooperation among local governments (prefectures) for seed production and release of certain targeted species in order to reduce the cost and improve the efficiency of stock enhancement. In Japan, traditionally, the purpose for release was mainly sea ranching, namely harvesting all released animals. Nowadays, actual resource enhancement, i.e. the integrated release program including resource management and development of suitable nursery for released fish, is encouraged by the government. The evaluation and counter measures for the negative impact of stocked fish on genetic diversity of the wild population are also implemented. Recently, marked progress was achieved in seed production technologies of two important tropical fish species, namely coral trout, Plectropomus leopardus, and humphead wrasse, Cheilinus undulatus. These technologies are expected to contribute to the advancement of the aquaculture industry in the South East Asian region

Ambipolar suppression of superconductivity by ionic gating in optimally-doped BaFe2(As,P)2 ultrathin films

Superconductivity (SC) in the Ba-122 family of iron-based compounds can be controlled by aliovalent or isovalent substitutions, applied external pressure, and strain, the combined effects of which are sometimes studied within the same sample. Most often, the result is limited to a shift of the SC dome to different doping values. In a few cases, the maximum SC transition at optimal doping can also be enhanced. In this work, we study the combination of charge doping together with isovalent P substitution and strain by performing ionic gating experiments on BaFe$_2$(As$_{0.8}$P$_{0.2}$)$_2$ ultrathin films. We show that the polarization of the ionic gate induces modulations to the normal-state transport properties that can be mainly ascribed to surface charge doping. We demonstrate that ionic gating can only shift the system away from the optimal conditions, as the SC transition temperature is suppressed by both electron and hole doping. We also observe a broadening of the resistive transition, which suggests that the SC order parameter is modulated nonhomogeneously across the film thickness, in contrast with earlier reports on charge-doped standard BCS superconductors and cuprates.Comment: 10 pages, 5 figure

Nanoscale Texture and Microstructure in a NdFeAs(O,F)/IBAD-MgO Superconducting Thin Film with Superior Critical Current Properties

This paper reports the nanoscale texture and microstructure of a high-performance NdFeAs(O,F) superconducting thin film grown by molecular beam epitaxy on a textured MgO/Y2O3/Hastelloy substrate. The NdFeAs(O,F) film forms a highly textured columnar grain structure by epitaxial growth on the MgO template. Although the film contains stacking faults along the ab-plane as well as grain boundaries perpendicular to the ab-plane, good superconducting properties are measured: a critical temperature, T-c, of 46 K and a self-field critical current density, J(c), of 2 x 10(6) A/cm(2) at 4.2 K. Automated crystal orientation mapping by scanning precession electron diffraction in transmission electron microscope is employed to analyze the misorientation angles between adjacent grains in a large ensemble (247 grains), and 99% of the grain boundaries show in-plane misorientation angles (Delta gamma) less than the critical angle theta(c), which satisfies one of the necessary conditions for the high J(c). Comparing the columnar grain size distribution with the mean distance of the flux line lattice, the triple junctions of low-angle grain boundaries are found to be effective pinning centers, even at high temperatures (>= 35 K) and/or low magnetic fields

High Jc_{c} and low anisotropy of hydrogen doped NdFeAsO superconducting thin film

The recent realisations of hydrogen doped LnFeAsO (Ln = Nd and Sm) superconducting epitaxial thin films call for further investigation of their structural and electrical transport properties. Here, we report on the microstructure of a NdFeAs(O,H) epitaxial thin film and its temperature, field, and orientation dependencies of the resistivity and the critical current density J$_{c}$. The superconducting transition temperature T$_{c}$ is comparable to NdFeAs(O,F). Transmission electron microscopy investigation supported that hydrogen is homogenously substituted for oxygen. A high self-field J$_{c}$ of over 10 MA/cm$^{2}$ was recorded at 5 K, which is likely to be caused by a short London penetration depth. The anisotropic Ginzburg–Landau scaling for the angle dependence of J$_{c}$ yielded temperature-dependent scaling parameters γ$_{J}$ that decreased from 1.6 at 30 K to 1.3 at 5 K. This is opposite to the behaviour of NdFeAs(O,F). Additionally, γ$_{J}$ of NdFeAs(O,H) is smaller than that of NdFeAs(O,F). Our results indicate that heavily electron doping by means of hydrogen substitution for oxygen in LnFeAsO is highly beneficial for achieving high J$_{c}$ with low anisotropy without compromising T$_{c}$, which is favourable for high-field magnet applications

Microscopic origin of highly enhanced current carrying capabilities of thin NdFeAs(O,F) films

Fe-based superconductors present a large variety of compounds whose physical properties strongly depend on the crystal structure and chemical composition. Among them, the so-called 1111 compounds show the highest critical temperature T(c) in the bulk form. Here we demonstrate the realization of excellent superconducting properties in NdFeAs(O(1−x)F(x)). We systematically investigated the correlation between the microstructure at the nanoscale and superconductivity in an epitaxial 22 nm NdFeAs(O(1−x)F(x)) thin film on a MgO single crystalline substrate (T(c) = 44.7 K). Atomic resolution analysis of the microstructure by transmission electron microscopy and atom probe tomography identified several defects and other inhomogeneities at the nanoscale that can act as extrinsic pinning centers. X-Ray diffraction and transmission electron microscopy displayed a broad variation of the a-axis lattice parameter either due to a partially strained layer at the interface to the substrate, high local strain at dislocation arrays, mosaicity, or due to composition variation within the film. The electrical transport properties are substantially affected by intrinsic pinning and a matching field corresponding to the film thickness and associated with the Bean–Livingston surface barrier of the surfaces. The thin film showed a self-field critical current density J(c)(4.2 K) of ∼7.6 MA cm(−2) and a record pinning force density of F(p) ≈ 1 TN m(−3) near 35 T for H‖ab at 4.2 K. These investigations highlight the role of the microstructure in fine-tuning and possibly functionalizing the superconductivity of Fe-based superconductors