A nanoscale SQUID operating at high magnetic fields

A washer-free Nb nanoSQUID has been developed for measuring magnetization changes from nanoscale objects. The SQUID loop is etched into a 250 nm wide Au/Nb bilayer track and the diameter of the SQUID hole is ~ 70 nm. In the presence of a magnetic field perpendicular to the plane of the SQUID, vortex penetration into the 250 nm wide track can be observed via the critical current–applied field characteristic and the value at which vortex first penetrates is consistent with the theoretical prediction. Upon removing the applied field, the penetrated vortices escape the track and the critical current at zero field is restored.

Oceanic long-distance navigation : do experienced migrants use the earth's magnetic field?

Albatrosses and sea turtles are known to perform extremely long-distance journeys between disparate feeding areas and breeding sites located on small, isolated, oceanic islands or at specific coastal sites. These oceanic journeys, performed mainly over or through apparently featureless mediums, indicate impressive navigational abilities, and the sensory mechanisms used are still largely unknown. This research used three different approaches to investigate whether bi-coordinate navigation based on magnetic field gradients is likely to explain the navigational performance of wandering albatrosses in the South Atlantic and Indian Oceans and of green turtles breeding on Ascension Island in the South Atlantic Ocean. The possibility that magnetic field parameters can potentially be used in a bi-coordinate magnetic map by wandering albatrosses in their foraging area was investigated by analysing satellite telemetry data published in the literature. The possibilities for using bi-coordinate magnetic navigation varied widely between different areas of the Southern Oceans, indicating that a common mechanism, based on a bi-coordinate geomagnetic map alone, was unlikely for navigation in these areas. In the second approach, satellite telemetry was used to investigate whether Ascension Island green turtles use magnetic information for navigation during migration from their breeding island to foraging areas in Brazilian coastal waters. Disturbing magnets were applied to the heads and carapaces of the turtles, but these appeared to have little effect on their ability to navigate. The only possible effect observed was that some of the turtles with magnets attached were heading for foraging areas slightly south of the control turtles along the Brazilian coast. In the third approach, breeding female green turtles were deliberately displaced in the waters around Ascension Island to investigate which cues these turtles might use to locate and return to the island; the results suggested that cues transported by wind might be involved in the final stages of navigation.

Epoxy nanocomposites containing magnetite-carbon nanofibers aligned using a weak magnetic field

Abstract Novel magnetite-carbon nanofiber hybrids (denoted by Fe3O4@CNFs) have been developed by coating carbon nanofibers (CNFs) with magnetite nanoparticles in order to align CNFs in epoxy using a relatively weak magnetic field. Experimental results have shown that a weak magnetic field (∼mT) can align these newly-developed nanofiber hybrids to form a chain-like structure in the epoxy resin. Upon curing, the epoxy nanocomposites containing the aligned Fe3O4@CNFs show (i) greatly improved electrical conductivity in the alignment direction and (ii) significantly higher fracture toughness when the Fe3O4@CNFs are aligned normal to the crack surface, compared to the nanocomposites containing randomly-oriented Fe3O4@CNFs. The mechanisms underpinning the significant improvements in the fracture toughness have been identified, including interfacial debonding, pull-out, crack bridging and rupture of the Fe3O4@CNFs, and plastic void growth in the polymer matrix.

Bubble flow in a static magnetic field

A lab-based electrolytic-cell is designed to analyze the effect of external magnetic field on bubble evolution underneath an anode surface. Buckingham Pi theorem is used to provide a complete list of dimensionless parameters for a typical cell configuration. There is an increase in bubble size and the number of bubbles with time. The hydrodynamic convection is apparent due to the effect of electrolyte flow caused by swarm of bubbles rising along the anode surface. The image sequence shows that swarm of bubbles exhibit a swirling flow-field in the presence of the magnetic field. The coalescence process intensifies in an area where magnetic field is higher. As a consequence, bubbles are swept away by the magneto-hydrodynamic (MHD) convection. These results suggest that a magnetic field causes remarkable improvement on the surface coverage of the anode.

A novel route for tethering graphene with iron oxide and its magnetic field alignment in polymer nanocomposites

We present a new route of tethering graphene nanoplatelets (GNPs) with Fe3O4 nanoparticles to enable their alignment in an epoxy using a weak magnetic field. The GNPs are first stabilised in water using polyvinylpyrrolidone (PVP) and Fe3O4 nanoparticles are then attached via co-precipitation. The resultant Fe3O4/PVP-GNPs nanohybrids are superparamagnetic and can be aligned in an epoxy resin, before gelation, by applying a weak magnetic field as low as 0.009 T. A theoretical model describing the alignment process is presented and used to quantify the effects of key parameters on the time needed for the alignment process. Compared to the unmodified epoxy, the resulting epoxy polymer nanocomposites containing randomly-oriented Fe3O4/PVP-GNPs nanohybrids exhibit significantly improved electrical conductivities by up to three orders of magnitude and fracture energies by up to 300%. The alignment of the Fe3O4/PVP-GNPs nanohybrids in the epoxy polymer nanocomposites transverse to the direction of crack propagation further increased the fracture energy by 50%, and the electrical conductivity by seven fold in the alignment direction, compared to the nanocomposites containing randomly-oriented nanohybrids.

Electrolyte flow in an external magnetic field: a dimensionless analysis

In this paper, some recent work on the flow induced by an external magnetic fields acting on electrochemical cell is reviewed. Although the influence of the magnetic field on the hydrodynamics has been studied for over 5 decades, the magnetohydrodynamics (MHD) remains relatively unfamiliar to all but a few research groups. There are nearly a countless number of dimensionless parameters in electrolytic flow (bubble induced flow) and MHD, but they have been introduced for convenience by different authors. The similitude parameter proposed by Solheim, Johansen, Rolseth, and Thonstad (1989) and Perron, Kiss, and Poncsák (2006) have been modified to provide a full set of parameters for electrolytic cell operating under external magnetic field. The bubble sliding characteristics underneath an inclined plane are studied using copper sulphate solution (as an electrolyte) in lab-based-scale and discussed.

Orientation relationship, texture and microstructure in electromagnetic processed materials (EPM)

In this work, some of our recent results in microstructure, texture and orientation relationship resulting from the application of an external high magnetic field during diffusional and non-diffusional phase transformation in both steel and functional metallic materials have been summarized. A 12-T magnetic field was applied to the diffusional decomposition of austenite in 0.81C-Fe alloy and martensitic transformation of a Ni-Mn-Ga magnetic shape memory alloy. For the 0.81C-Fe alloy, it was found that the magnetic field induces the formation of proeutectoid ferrite and slightly enhances the <001> fiber component in ferrite in the transverse field direction. The magnetic dipolar interaction between Fe atoms in the transverse field direction accounts for this phenomenon. The magnetic field favors the formation of pearlite with Pitsch-Petch 2 (P-P 2) and Isaichev (IS) orientation relationships (OR) between the lamellar ferrite and cementite. For the Ni-Mn-Ga magnetic shape memory alloy, the magnetic field makes the martensite lamellas to grow in some specific directions with their c-axes [001] orientated to the field direction and transverse field direction.

Vehicle detection and classification by measuring and processing magnetic signal

This paper presents novel vehicle detection and classification method by measuring and processing magnetic signal based on single micro-electro- mechanical system (MEMS) magnetic sensor. When a vehicle moves over the ground, it generates a succession of impacts on the earth's magnetic field, which can be detected by single magnetic sensor. The magnetic signal measured by the magnetic sensor is related to the moving direction and the type of the vehicle. Generally, the recognition rate using single sensor detector is not high. In order to improve the recognition rate, a novel feature extraction algorithm and a novel vehicle classification and recognition algorithm are presented. The concavity and convexity areas, and the angles of concave and convex parts of the waveform are extracted. An improved support vector machine (ISVM) classifier is developed to perform vehicle classification and recognition. The effectiveness of the proposed approach is verified by outdoor experiments.

Magnet-induced temporary superhydrophobic coatings from one-pot synthesized hydrophobic magnetic nanoparticles.

In this paper, we report on the production of superhydrophobic coatings on various substrates (e.g., glass slide, silicon wafer, aluminum foil, plastic film, nanofiber mat, textile fabrics) using hydrophobic magnetic nanoparticles and a magnet-assembly technique. Fe3O4 magnetic nanoparticles functionalized with a thin layer of fluoroalkyl silica on the surface were synthesized by one-step coprecipitation of Fe2+/Fe3+ under an alkaline condition in the presence of a fluorinated alkyl silane. Under a magnetic field, the magnetic nanoparticles can be easily deposited on any solid substrate to form a thin superhydrophobic coating with water contact angle as high as 172°, and the surface superhydrophobicity showed very little dependence on the substrate type. The particulate coating showed reasonable durability because of strong aggregation effect of nanoparticles, but the coating layer can be removed (e.g., by ultrasonication) to restore the original surface feature of the substrates. By comparison, the thin particle layer deposited under no magnetic field showed much lower hydrophobicity. The main reason for magnet-induced superhydrophobic surfaces is theformation of nano- and microstructured surface features. Such a magnet-induced temporary superhydrophobic coating may have wide applications in electronic, biomedical, and defense-related areas.

A little movement orientated to the geomagnetic field makes a big difference in strong flows

Whilst a range of animals have been shown to respond behaviourally to components of the Earth’s magnetic field, evidence of the value of this sensory perception for small animals advected by strong flows (wind/ocean currents) is equivocal. We added geomagnetic directional swimming behaviour for North Atlantic loggerhead turtle hatchlings (Caretta caretta) into a high-resolution (1/4°) global general circulation ocean model to simulate 2,925-year-long hatchling trajectories comprising 355,875 locations. A little directional swimming (1–3 h per day) had a major impact on trajectories; simulated hatchlings travelled further south into warmer water. As a result, thermal elevation of hatchling metabolic rates was estimated to be between 63.3 and 114.5% after 220 days. We show that even small animals in strong flows can benefit from geomagnetic orientation and thus the potential implications of directional swimming for other taxa may be broad.