Differences in the escape response of a grapsid crab in the field and in the laboratory

Escape behaviours of prey animals are frequently used to study the neural control of behaviour. Escape responses are robust, fast, and can be reliably evoked under both field and laboratory conditions. Many escape responses are not as simple as previously suggested, however, and are often modulated by a range of contextual factors. To date it has been unclear to what extent behaviours studied in controlled laboratory experiments are actually representative of the behaviours that occur under more natural conditions. Here we have used the model species, Neohelice granulata, a grapsid crab, to show that there are significant differences between the crabs' escape responses in the field compared to those previously documented in laboratory experiments. These differences are consistent with contextual adjustments such as the availability of a refuge and have clear consequences for understanding the crabs' neural control of behaviour. Furthermore, the methodology used in this study mirrors the methodology previously used in fiddler crab research, allowing us to show that the previously documented differences in escape responses between these grapsid species are real and substantial. Neohelice's responses are delayed and more controlled. Overall, the results highlight the adaptability and flexibility of escape behaviours and provide further evidence that the neural control of behaviour needs to be address in both the laboratory and field context.Fil: Hemmi, J. M.. University of Western Australia; AustraliaFil: Tomsic, Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Fisiología, Biología Molecular y Neurociencias. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Fisiología, Biología Molecular y Neurociencias; Argentin

Transport critical current of Solenoidal MgB2/Cu Coils Fabricated Using a Wind-Reaction In-situ Technique

In this letter, we report the results of transport Jc of solenoid coils upto 100 turns fabricated with Cu-sheathed MgB2 wires using a wind-reaction in-situ technique. Despite the low density of single core and some reaction between Mg and Cu-sheath, our results demonstrate the decrease in transport Jc with increasing length of MgB2 wires is insignificant. Solenoid coils with diameter as small as 10 mm can be readily fabricated using a wind-reaction in-situ technique. The Jc of coils is essentially the same as in the form of straight wires. A Jc of 133,000 A/cm2 and 125,000 A/cm2 at 4 K and self field has been achieved for a small coil wound using Cu-sheathed tape and Cu-sheathed wire respectively. These results indicate that the MgB2 wires have a great potential for lage scale applicationsComment: 6 pages, 4 figures, 1 tabl

Critical Current Density and Current Transfer Length of Multifilamentary MgB2 Strands of Various Design

In this paper, a series of high performing PIT MgB2 strands have been prepared. Transport voltage-current measurements were performed to determine the effects of C doping and strand geometry such as filament numbers. The best Jc for our samples was 1.0 × 105 A/cm2 at 4.2 K, 7 T, for a strand using B powder with 3% C addition. The current transfer length (CTL) was also measured for MgB2 short wires with Nb chemical barrier and Monel outer sheath. The CTL ranged from 2-12 mm, and had a correlation with the filament numbers.This work was supported by the U.S. Department of Energy, High Energy Physics grant DE-FG02-95ER40900, and a DOE SBIR.The in-field critical current densities of a set of in situ CTFF-type PIT MgB2 strands have been investigated in terms of C doping level, wire diameter and filament number. The strand with optimal doping level – 3% C achieved the best Jc of 1.0 × 105 A/cm2 at 4.2 K, 7 T. By fitting it with the percolation model, the parameters showed that the Bc2 and the flux pinning strength was improved and the anisotropy ratio was reduced. Increases in filament count did not change Jc, although n-values were higher for the monocore strand. The current transfer length of MgB2 strands with Nb chemical barriers and Monel sheaths increased with filament count. The CTL was less than 3.7 mm for the monocore strand, and it ranged from 2.2-11.8 mm for the 24- filamentary strand D2, depending on the applied field

The critical current density of advanced internal-Mg-diffusion-processed MgB2 wires

Recent advances in MgB2 conductors are leading to a new level of performance. Based on the use of proper powders, proper chemistry, and an architecture which incorporates internal Mg diffusion (IMD), a dense MgB2 structure with not only a high critical current density Jc, but also a high engineering critical current density, Je, can be obtained. In this paper, a series of these advanced (or second - generation, "2G") conductors has been prepared. Scanning electron microscopy and associated energy dispersive X-ray spectroscopy were applied to characterize the microstructures and compositions of the wires, and a dense MgB2 layer structure was observed. The best layer Jc for our sample is 1.07x105 A/cm2 at 10 T, 4.2 K, and our best Je is seen to be 1.67x104 A/cm2 at 10 T, 4.2 K. Optimization of the transport properties of these advanced wires is discussed in terms of B-powder choice, area fraction, and the MgB2 layer growth mechanism.Comment: 13 pages, 3 tables, 7 figures (or 8 pp in published version