Shell Volume Research Articles

Review of Domain Wall Dynamics Engineering in Magnetic Microwires.

The influence of magnetic anisotropy, post-processing conditions, and defects on the domain wall (DW) dynamics of amorphous and nanocrystalline Fe-, Ni-, and Co-rich microwires with spontaneous and annealing-induced magnetic bistability has been thoroughly analyzed, with an emphasis placed on the influence of magnetoelastic, induced and magnetocrystalline anisotropies. Minimizing magnetoelastic anisotropy, either by the selection of a chemical composition with a low magnetostriction coefficient or by heat treatment, is an appropriate route for DW dynamics optimization in magnetic microwires. Stress-annealing allows further improvement of DW velocity and hence is a promising method for optimization of DW dynamics in magnetic microwires. The origin of current-driven DW propagation in annealing-induced magnetic bistability is attributed to magnetostatic interaction of outer domain shell with transverse magnetization orientation and inner axially magnetized core. The beneficial influence of the stress-annealing on DW dynamics has been explained considering that it allows increasing of the volume of outer domain shell with transverse magnetization orientation at the expense of decreasing the radius of inner axially magnetized core. Such transverse magnetic anisotropy can similarly affect the DW dynamics as the applied transverse magnetic field and hence is beneficial for DW dynamics optimization. Stress-annealing allows designing the magnetic anisotropy distribution more favorable for the DW dynamics improvement. Results on DW dynamics in various families of nanocrystalline microwires are provided. The role of saturation magnetization on DW mobility improvement is discussed. The DW shape, its correlation with the magnetic anisotropy constant and the microwire diameter, as well as manipulation of the DW shape by induced magnetic anisotropy are discussed. The engineering of DW propagation through local stress-annealing and DW collision is demonstrated.

Frenopyxis stierlitzi gen. nov., sp. nov.-new testate amoeba (Amoebozoa: Arcellinida) from the urban parks with notes on the systematics of the family Centropyxidae Jung, 1942.

New species, Frenopyxis stierlitzi, is described from tree hollows in the urban parks in Moscow (Russia) and Potsdam (Germany). The species belongs to the new genus of the family Centropyxidae and characterized by unique character, i.e. an internal thick organic lip surrounding an aperture and continuing in a bridle, which connects an aperture with the internal side of a shell wall and broaden in the place of connection of a bridle and a shell wall. The systematics of the family Centropyxidae is discussed and the importance of the structures, which divide inner shell volume into compartments, is underlined.

STATISTICS OF FAILURES AND MONITORING OF THE STATE OF POOLS AND PROTECTIVE HERMETIC FENCES OF NUCLEAR POWER PLANTS

Assessment of the technical condition of the main systems and structures is one of the main stage tasks of technical diagnostics of NPP elements. One of the important elements of the hermetic volume of the protective shells of nuclear power plants is a storage pool (SP) of spent nuclear fuel (SNF). For provision of SNF storage the appropriate systems and structures are used: SNF handling system, SP cooling system and SP by itself. Pools are made of monolithic reinforced concrete with stainless steel lining intended to retain cooling water (boric acid solution) and protect the concrete from direct effect of aggressive environments. Emergency leaks may occur through the SP lining during operation of a nuclear power plant. Materials used for pool structures must be radiation resistant and resistant to a boric acid solution. The structure of the storage pool must be earthquake-proof, must allow monitoring of emergency leaks and maintain a controlled water level in case of leaks for the time period until the fuel will be discharged. Features of failures during operation, results of research and recommendations for extending the service life of storage pools at domestic nuclear power plants with VVER are considered. Assessment of the technical condition of the main structures of the SP provides for specialized research. Thus, the SP survey generally involves visual and instrumental examination of the bottom lining, internal lining, as well as concrete walls and bottom.

Larvicidal Activity of Aedes Aegypti from a Simple Preparation of Cashew (Anacardium occidentale L.) Nut Shell Extract for Community Level Use

Dengue fever is a major risk to public health due to the recent worldwide spread. Chemical vector control areusually considered, therefore, negative consequences are commonly occurred due to chemical resistance andenvironmental effects. Volume of cashew nut shell is become increasing as by-product after nut processing.This study was aimed to evaluate larvicial activity and toxicity of cashew shell extract with simple preparationfor community use. Fresh cashew nut shell was dried and grinded in powder form. Material was immersed inwater tank for 72 h and ratio of flavor and material and water ratio was 100 g/L (10% W/V). The supernatantof stock solution was diluted to 1:5, 1:10, 1:20, 1:50 and 1:100 of larvicidal solution for phenolic contentmeasurement, analysis of alkyl phenols by gas chromatography-mass spectrometry (GC/MS) and larvicialactivity test. Larvicidal activity was effective at LC50 = 3.8 mg of GAE/ml; LC90 = 11.5 mg of gallic acidequivalent (GAE) /ml. The solution was contained five alkyl phenols, which included saturated cardol,monounsaturated cardol, anacardic acid, diunsaturated cardanol and monounsaturated cardanol. Anacardicacid was major active compound, which was correlated to mass spectra. This larvicidal solution preparationwas simple and cost effectiveness, which may useful in community level especially in cashew cultivatingarea. Field application and public training on this study will be conduct on controlling of mosquito-bornediseases.

Aprovechamiento de cenizas volantes y sedimentables provenientes de la valorización energética de cáscaras de maní, como materia prima de la industria cerámica.

Las industrias de la región productora de maní, luego de su recolección primaria y posterior procesamiento, acumulan como residuo de este proceso un gran volumen de cáscaras de maní, que han comenzado a ser quemadas con el fin de aprovecharlas para producción de energía. Los residuos inorgánicos que se originan en dicho proceso biomasa-energía, son cenizas volantes o finas y cenizas sedimentables o gruesas, y no tienen al momento un aprovechamiento eficaz, por lo que se propone establecer la factibilidad de su reutilización como materia prima para la fabricación de materiales cerámicos. Se propone, además de la necesidad de resolver la actual disposición final de estos residuos secundarios inorgánicos desde una visión netamente ambiental, valorizar dichos residuos como materia prima de la industria de la construcción, e involucrar en el desarrollo de este trabajo el concepto de economía circular y todos los beneficios asociados a su aplicación a través de herramientas tales como análisis de ciclo de vida (ACV) y huella de carbono, entre otras.

Effects of liquid compressibility on the dynamics of ultrasound contrast agent microbubbles

Ultrasound contrast agents (UCA) have been widely used in ultrasonic medical applications. The dynamics of UCA should be simulated accurately to maximize the application effects. The acoustic radiation of UCA oscillations is affected by the liquid compressibility which has to be considered. This paper deduces a simple equation based on Keller-Miksis equation to describe the dynamics of UCA with a polymer shell, taking consideration of compressibility of the liquid. The volume of UCA shell is constant. The shell is described by the Kelvin-Voigt viscoelasticity model.The extended compressible model is verified by comparing with experimental data and Hoff model in predicting the variations of bubble radius with time, resonance frequency, damping constants and acoustical scattering cross section of the UCA microbubbles. The physical explanations of the differences between the extended compressible model and Hoff model in predicting resonance frequency and acoustical scattering cross section are listed. The liquid compressibility correction in UCA model can be better used to predict the bubble dynamics at large radius with high excitation frequency, and it will give us some valuable references in ultrasonic medical applications.

Diminishing returns in habitat restoration by adding biogenic materials: a test using estuarine oysters and recycled oyster shell

Restoration of degraded estuarine oyster reefs typically involves deploying recycled oyster shell. In low‐salinity, low‐predation areas of estuaries, high‐volume shell deployments are known to improve flow conditions and thus oyster survival and growth. It is also hypothesized that the physical structure of restored reefs could suppress foraging by oyster predators in high‐salinity, high‐predation zones. That hypothesis is untested. Given limited resources, it is important to determine how much shell is needed for successful restoration and whether there are diminishing returns in shell addition. In Apalachicola Bay, Florida, we manipulated shell volume on an oyster reef to create three 0.4 ha areas of low (no shell addition), moderate (153 m3 shell), and high (306 m3 shell) habitat structure. We repeated experiments and surveys over 2 years to determine if restoration success increased with habitat structure. Predation on oysters was greater on the non‐shelled area than on the reshelled reefs, but similar between the two reshelled reefs. Oyster larval supply did not differ among the reef areas, but by the end of the experiment, oyster density (per unit area) increased quadratically with habitat structure, plateauing at high levels of structure. Model selection indicated that the most parsimonious explanation for these patterns was that increased habitat structure reduced predation and increased overall recruitment, but that the higher reshelling treatment did not have better outcomes than moderate reshelling. Thus, restoration could be optimized by deploying a moderate amount of shell per unit area.

Effect of Shell Pore Microstructure of the Pd Hollow Catalysts Pd@HMAN for H2O2 Generation

Pd-based hollow catalysts, Pd@HMAN, in which Pd was used as core and hollow aluminosilicate (HMAN) as shell, have been successfully synthesized by self-assembling method. Pd@HMAN-M (M = 1, 1.5, 2, 2.5) with uniform Pd nanoparticle size (~ 9.3 nm) and different shell volume (0.06–0.18 cm3g−1) were prepared by varying the addition amount of tetraethyl orthosilicate (TEOS). It is found that the shell pore size of 1–3.5 nm of the catalysts Pd@HMAN-M was conducive to the mass transfer of H2, O2 and H2O2, and the larger the shell pore volume of Pd@HMAN-M was, the larger the adsorption amount of reactant H2 was, and thus the higher selective and productive of H2O2 could be obtained. The catalyst Pd@HMAN-1.5 had the highest H2O2 selectivity (81%) and productivity (795 mmol gPd−1 h−1) at atmospheric pressure due to its most substantial shell pore volume of (0.18 cm3g−1) and H2 adsorption amount.

Usos potenciales de la cáscara de huevo de gallina (Gallus gallus domesticus): una revisión sistemática

El huevo de gallina (Gallus gallus domesticus) es uno de los alimentos de mayor consumo a nivel mundial y en el caso específico de Colombia. Según la Federación Nacional de Avicultores-(FENAVI), en el año 2018 el consumo per-capital fue de 293 unidades. Este consumo genera un elevado volumen de cáscara como residuo, lo que lleva a los investigadores a interesarse en su aprovechamiento en diversas áreas, propiciando el desarrollo de emprendimientos. Además, sería un aspecto bastante negativo para el impacto ambiental, debido al manejo inadecuado de los residuos ordinarios, como es el caso de la cáscara de huevo, convirtiéndose en un factor de riesgo para la sostenibilidad y la sustentabilidad ambiental. Esta revisión muestra estudios del aprovechamiento de la cáscara como residuo agroalimentario en diferentes áreas, tales como la industria farmacéutica, química, cosmética y alimentaria. Su alto contenido en carbonato de calcio y otros constituyentes minoritarios como hidróxido de calcio, carbonato de magnesio, fosfato de calcio, sustancias orgánicas y en su membrana proteínas como el colágeno y el ácido hialurónico, la hacen una materia prima única y polifuncional.

Shell utilization pattern by the hermit crab Diogenes custos (Fabricius, 1798) along Gulf of Kachchh, Gujarat, India

Present work aims to study the gastropod shell utilization pattern of hermit crab Diogenes custos in the intertidal zone of Gulf of Kachchh, Gujarat, India. Hermit crab specimens were collected randomly during the low tide timings using hand picking method in February 2019 and November 2019. Data on abundance of common gastropod species were also collected using a quadrate sampling method. Hermit crab wet weight (HW) and their shield length (SL) (represent the size of the hermit crabs) were measured. Gastropod shells were identified up to species level and different morphological characters such as shell dry weight (DW), shell length (SHL), shell volume (SHV), shell aperture length (SAL), and shell aperture width (SAW) were measured. Total 2000 individuals of D. Custos, 1171 males (58.6%), 763 females (38.1%) and 66 ovigerous females (3.3%) occupying 49 species of gastropods were collected. Pollia undosa (21.9%) was highly occupied by D. custos followed by Cantharus spiralis (14.5%), Tenguella granulata (9.9%), Chicoreus virgineus (6.45%), Cerithium caeruleum (6.05%) and Nassarius distortus (6.05%). Regression analysis carried out between D. custos morphological characters and gastropod shell morphological characters showed a strong relationship which suggests that shell architecture plays an important role in shell utilization pattern of Diogenes custos. The abundance of Pollia undosa was very high in the intertidal zone as compared to other commonly occupied gastropods species which also suggests that gastropod shell availability in the habitat also has pronounced effect on shell utilization pattern of D. custos.

Hierarchical Structural Changes During Redox Cycling of Fe-Based Lamellar Foams Containing YSZ, CeO2, or ZrO2.

Several high-temperature energy conversion and storage technologies rely on redox cycling of Fe-based materials, including storage materials in solid-oxide Fe-air batteries and oxygen carriers in chemical-looping combustion. The materials' macroporosity necessary for gas flow is, however, irreversibly diminished during redox cycling due to (i) large volume changes during the redox transformations, (ii) foam sintering at elevated operating temperature (550-900 °C), and (iii) formation and growth of Kirkendall microporosity. To address these challenges, we use directional freeze-casting to create highly porous, lamellar, Fe-composite foams containing uniformly distributed sintering inhibitor (SI) particles-either Y2O3-stabilized ZrO2 (YSZ), CeO2, or ZrO2-at 0, 5, 10, or 15% of the solid volume. We characterize these foams before, during, and after redox cycling (Fe/FeO/Fe3O4, via H2O and H2) at 800 °C using operando synchrotron X-ray microtomography, metallography, and scanning electron microscopy. Shrinkage of the foam volume and formation of a gas-blocking shell surrounding the foam are reduced as the SI fraction increases. Volumetric shrinkage after the first five redox cycles is decreased from 66% (for pure-Fe foams) to 45% (for all Fe-composites containing 5 vol % SI). Foams containing 15 vol % YSZ show no volumetric shrinkage after five cycles, although, after 20 cycles, they have shrunk 53%. Post-cycling analysis reveals segregation of the SI particles to the cores of individual lamellae, surrounded by thick layers of sintered Fe on the lamellae surfaces. This segregation occurs due to Fe diffusion through FeO to the lamellae surfaces during oxidation, leaving behind the SI particles, which are then pushed into clusters by FeO/Fe3O4 contraction during reduction. The SI is thus rendered ineffective, which explains why foam densification is delayed (compared with pure-Fe foams), rather than fully prevented, after repeated cycling.

Controlling the domain wall dynamics in Fe-, Ni- and Co-based magnetic microwires

Abstract We studied influence of post-processing (annealing and stress-annealing) on domain wall dynamics in Fe-, Ni- and Co-based magnetic microwires with spontaneous and induced magnetic bistability. As-prepared Co-based microwires with low and negative magnetostriction present linear hysteresis loops. Magnetic bistability in Co-based microwires has been induced by annealing. Minimizing magnetoelastic anisotropy either by adjusting the chemical composition with a low magnetostriction coefficient or by heat treatment is an appropriate route for the domain wall dynamics optimization in magnetic microwires. Stress-annealing allows further improvement of domain wall velocity and hence is a promising method allowing optimization of the DW dynamics in magnetic microwires. The beneficial influence of stress-annealing on the DW dynamics is explained considering an increase in the volume of outer domain shell with transverse magnetization orientation in expense of decrease in the radius of the inner axially magnetized core. Such transverse magnetic anisotropy can affect the DW dynamics in similar way as the applied transverse magnetic field and hence is beneficial for the DW dynamics optimization. Thus, stress-annealing allows designing the magnetic anisotropy distribution more favorable for the DW dynamics improvement. Co-rich microwires with magnetic bistability induced by annealing present a considerable enhancement in the DW velocity upon applied tensile stress: exactly the opposite to the case of magnetic microwires with spontaneous magnetic bistability. Observed dependence has been explained considering decrease in the magnetostriction coefficient under effect of the applied stress.

Determining how biotic and abiotic variables affect the shell condition and parameters of <i>Heliconoides inflatus</i> pteropods from a sediment trap in the Cariaco Basin

Abstract. Pteropods have been nicknamed the “canary in the coal mine” for ocean acidification because they are predicted to be among the first organisms to be affected by changing ocean chemistry. This is due to their fragile, aragonitic shells and high abundances in polar and subpolar regions where the impacts of ocean acidification are most pronounced. For pteropods to be used most effectively as indicators of ocean acidification, the biotic and abiotic factors influencing their shell formation and dissolution in the modern ocean need to be quantified and understood. Here, we measured the shell condition (i.e., the degree to which a shell has dissolved) and shell characteristics, including size, number of whorls, shell thickness, and shell volume (i.e., amount of shell material) of nearly 50 specimens of the pteropod species Heliconoides inflatus sampled from a sediment trap in the Cariaco Basin, Venezuela, over an 11-month period. The shell condition of pteropods from sediment traps has the potential to be altered at three stages: (1) when the organisms are live in the water column associated with ocean acidification, (2) when organisms are dead in the water column associated with biotic decay of organic matter and/or abiotic dissolution associated with ocean acidification, and (3) when organisms are in the closed sediment trap cup associated with abiotic alteration by the preservation solution. Shell condition was assessed using two methods: the Limacina Dissolution Index (LDX) and the opacity method. The opacity method was found to capture changes in shell condition only in the early stages of dissolution, whereas the LDX recorded dissolution changes over a much larger range. Because the water in the Cariaco Basin is supersaturated with respect to aragonite year-round, we assume no dissolution occurred during life, and there is no evidence that shell condition deteriorated with the length of time in the sediment trap. Light microscope and scanning electron microscope (SEM) images show the majority of alteration happened to dead pteropods while in the water column associated with the decay of organic matter. The most altered shells occurred in samples collected in September and October when water temperatures were warmest and when the amount of organic matter degradation, both within the shells of dead specimens and in the water column, was likely to have been the greatest. The hydrographic and chemical properties of the Cariaco Basin vary seasonally due to the movement of the Intertropical Convergence Zone (ITCZ). Shells of H. inflatus varied in size, number of whorls, and thickness throughout the year. There was not a strong correlation between the number of whorls and the shell diameter, suggesting that shell growth is plastic. H. inflatus formed shells that were 40 % thicker and 20 % larger in diameter during nutrient-rich, upwelling times when food supply was abundant, indicating that shell growth in this aragonite-supersaturated basin is controlled by food availability. This study produces a baseline dataset of the variability in shell characteristics of H. inflatus pteropods in the Cariaco Basin and documents the controls on alteration of specimens captured via sediment traps. The methodology outlined for assessing shell parameters establishes a protocol for generating similar baseline records for pteropod populations globally.

A Morphological Analysis of the Flat-Shaped Spumellarian Radiolarian Dictyocoryne: Morpho-Functional Insights into Planktonic Mode of Life

Abstract. The three-dimensional morphology of the flat-shaped spumellarian radiolarian Dictyocoryne was analysed using a microfocus X-ray CT with a special focus on whether it was capable of a planktonic lifestyle. Two types of 3D models, the shell model, which represents a realistic 3D shell, and the wrapped model, which mimics the whole body outline without pseudopodia, were reconstructed in order to estimate volume, surface area, and centres of gravity for the shell model and buoyancy for the wrapped model. The calculated values showed that the volume of shell with respect to the total volume was negatively allometric, regardless of the differences between threshold settings. Stepwise secretions of the patagium layer may result in a comparatively lightweight shell, thereby decreasing the total density during growth but not below the density of seawater. Estimated positions for the centres of gravity and buoyancy were too close to maintain an autonomous posture while floating. Instead, the ratio between surface area and volume was greater than that in an ideal sphere. Such a broad surface area could obtain the viscous resistance necessary for sinking retardation. Spumellarian radiolarians, including Dictyocoryne, have photosynthetic symbionts located primarily in the ectoplasmic layer, which is a habitable space that can be maximised within the larger surface area. Given that radiolarians float when extending their pseudopodia, it can be hypothesised that pseudopodia may play a role in the adjustment of life posture in a hydraulically unstable shell, which can be integrated into sinking retardation, enhancement of photosynthetic activity and manoeuvrability of life posture within a unique flat-shaped morphogenesis.

Finite element formulation to study thermal stresses in nanoencapsulated phase change materials for energy storage

Nanoencapsulated phase change materials (nePCMs) – which are composed of a core with a phase change material and of a shell that envelopes the core – are currently under research for heat storage applications. Mechanically, one problem encountered in the synthesis of nePCMs is the failure of the shell due to thermal stresses during heating/cooling cycles. Thus, a compromise between shell and core volumes must be found to guarantee both mechanical reliability and heat storage capacity. At present, this compromise is commonly achieved by trial and error experiments or by using simple analytical solutions. On this ground, the current work presents a thermodynamically consistent and three-dimensional finite element (FE) formulation considering both solid and liquid phases to study thermal stresses in nePCMs. Despite the fact that there are several phase change FE formulations in the literature, the main novelty of the present work is its monolithic coupling – no staggered approaches are required – between thermal and mechanical fields. Then, the FE formulation is implemented in a computational code and it is validated against one-dimensional analytical solutions. Finally, the FE model is used to perform a thermal stress analysis for different nePCM geometries and materials to predict their mechanical failure by using Rankine’s criterion.

Quantification of the Photon Absorption, Scattering, and On-Resonance Emission Properties of CdSe/CdS Core/Shell Quantum Dots: Effect of Shell Geometry and Volumes.

Reliable quantification of the optical properties of fluorescent quantum dots (QDs) is critical for their photochemical, -physical, and -biological applications. Presented herein is the experimental quantification of photon scattering, absorption, and on-resonance-fluorescence (ORF) activities of CdSe/CdS core/shell fluorescent QDs as a function of the shell sizes and geometries. Four spherical QDs (SQDs) with different diameters and four rod-like QDs (RQDs) with different aspect ratios (ARs) have been analyzed using UV-vis, fluorescence, and the recent polarized resonance synchronous spectroscopic (PRS2) methods. All quantum dots are simultaneous absorbers and scatterers in the UV-vis wavelength region, and they all exhibit strong ORF emission in the wavelength regions where the QDs both absorb and emit. The absorption and scattering cross-sections of the CdS shell are linearly and quadratically, respectively, proportional to the shell volume for both the SQDs and RQDs. However, the effects of CdS shell coating on the core optical properties are different between SQDs and RQDs. For RQDs, increasing the CdS shell volume through the length elongation has no effect on either the peak wavelength or intensity of the CdSe core UV-vis absorption and ORF, but it reduces the QD fluorescence depolarization. In contrast, increasing CdS shell volume in the SQDs induces red-shift in the CdSe core peak UV-vis absorption and ORF wavelengths, and increases their peak cross-sections, but it has no effect on the SQD fluorescence depolarization. The RQD ORF cross-sections and quantum yields are significantly higher than their respective counterparts for the SQDs with similar particle sizes (volumes). While these new insights should be significant for the QD design, characterization, and applications, the methodology presented in this work is directly applicable for quantifying the optical activities of optically complex materials where the common UV-vis spectrometry and fluorescence spectroscopy are inadequate.

Dynamics of core–shell particle formation in drop-tube processed metastable monotectic alloys

We examine the apparent size of the core and shell as a function of cooling rate in core–shell particles of the metastable monotectic alloy Co-50 at% Cu, finding that the volume fraction of the core systematically increases with cooling rate and hence undercooling. A model for this variation is proposed. A Monte-Carlo simulation is used to correct for sectioning effects allowing the true core:shell volume ratio to be estimated. From this, and the observation of a second, spinodal, episode of liquid phase separation we are able to estimate the undercooling at solidification. This permits a calculation of the time available following liquid phase separation for the migration giving rise to the observed core–shell structure to occur and hence the required Marangoni velocity required to such migration.

Optimizing magnetoimpedance of amorphous microwires by nanocarbon-induced magnetic anisotropy

Approaches to modulate magnetoimpedance (MI) in amorphous wires mostly include annealing, ion irradiation, glass coating and patterning, which are mainly based on induction of transverse magnetic anisotropy. Here, through modulating the magnetization distribution across the wire and outer magnetic shell/ inner core ratio, enhanced magneto- and stress-impedance sensitivity were obtained. Such modulation was achieved by coating a Co-based melt-extracted wire with carbon nanotubes (CNT) and graphene oxide (GO) which induced different level of stresses allowing the increase in outer domain shell volume with helicoidal/circular-type magnetic anisotropy in expense of the axially magnetized inner core. Moreover, through controlling nanocarbon thickness, we demonstrated the validity of high frequency impedance measurements to map the magnetic microstructure across the wire and reveal the core–shell interaction and its contribution to MI. The improvement in transversal anisotropy was evidenced by a drastic increase in MI effect from 170% at 10 MHz for uncoated wire to 400% and 300% for CNT and GO-coated wires, respectively. Finally, by developing a planar model with a four-layer structure, the main features of MI curves were reproduced in the simulated curves. Our results establish a simple platform for the design of microwave materials towards a wide range of sensing applications.

Effects of Tidal Exposure on Bivalve Molluscs: First Stab at the Case of West African Mangrove Oyster (Crassostrea tulipa) in Benya Lagoon, Elmina, Ghana

It is widely recognized that growth of sessile intertidal organisms is largely driven by tidal exposure. However, data supporting exact manifestation of this effect on Crassostrea tulipa is lacking, limiting management of the species to enhance nutrition and livelihood opportunities for coastal communities in West Africa. We investigated the growth of the species at 3 tidal heights [13 – 22 cm, 23 – 32 cm and 33 – 41 cm] above neap tide mean low water (MLW)] focusing on 3 parameters, i.e. shell height, condition index (CI) and gonadal development. Three hundred and thirty-three individual oysters from 10 colonies randomly selected from 2 stations, 500 and 600 m from the sea, around an open lagoon were investigated. CI was determined as the ratio between dry meat weight and inner shell volume; gonadal development was determined via histological analysis of gonad tissues. Shell height and CI of the oyster increased with tidal elevation irrespective of whether they were closer to or further from the sea. These findings agree with reports on other bivalves, suggesting that short tidal inundation promotes growth of C. tulipa. In terms of gonads, five stages of development were identified; all occurred among oysters located at lowest tidal levels (13 – 22 cm above MLW), possibly due to continuous breeding as a result of increased food supply by long inundation. The proportion of ripe gonads increased with tidal height; ≈67% of gonads found at the highest tidal levels were ripe suggesting discontinuous breeding in the higher-level oysters.

Micromagnetic simulations of reversal magnetization in core ((Nd<sub>0.7</sub>, Ce<sub>0.3</sub>)<sub>2</sub>Fe<sub>14</sub>B)-shell (Nd<sub>2</sub>Fe<sub>14</sub>B) type

The effects of core size, shell thickness and shell distribution on the coercivity of single-grain core ((Nd<sub>0.7</sub>,Ce<sub>0.3</sub>)<sub>2</sub>Fe<sub>14</sub>B)-shell (Nd<sub>2</sub>Fe<sub>14</sub>B) magnets are studied by programming and modeling them through using the C++ language. All the micromagnetic simulations are carried out via object oriented micro magnetic framework (OOMMF). The results show that the coercivity decreases with the increase of core size when the shell thickness is constant. It is considered that for the grain, the increase in the size of the core leads the average magnetocrystalline anisotropy field to increase and the total demagnetization energy to increase, thereby contributing to the magnetization reversal occurring under a smaller external field. When the core size is unchanged, as the shell thickness increases gradually, the coercivity first increases and then decreases. The analysis of the position of the nucleation point shows that the reason why the coercivity increases in the early period is mainly that the nucleation point is located at the core-shell junction and belongs to the core. As the thickness of the shell increases, the exchange interaction effect between the magnetic moment of the shell and the one of the nucleation point is strengthened, so a larger external field is needed in the nucleation process. As for the decrease of the coercivity in the later period, the main reason is that the nucleation points are exactly the vertices of the shell (also the vertices of the grain), and the increase of the shell thickness conduces to increasing the total demagnetization energy, so the nucleation points can be formed under a smaller external magnetic field. With core size and shell volume kept unchanged, when the shell is distributed on the two easy-axis planes (i.e. the planes perpendicular to the easy axis) of the core, the coercivity of the magnet reaches a largest value. It is because that the nucleation points are located at the vertices of the shell (also the vertices of the grain), of which the magnetocrystalline anisotropy field is larger, and the demagnetization field is smaller. Via magnetocrystalline anisotropy field, the demagnetization energy, nucleation point, etc, the changes of coercivity in above cases can be explained.