Simulation studies on the magnetization of (RE)BCO bulk superconductors using various split-coil arrangements

Simulation studies were conducted on the magnetization of (RE)BCO (RE-Ba-Cu-O, where RE represents a rare earth element) bulk superconductors using various split-coil arrangements by solving the critical state equation using the commercial software FlexPDE. A pair of coaxial coils of identical size is identified as an optimum arrangement for practical magnetization at 77K by the zero-field cooling technique. In general, the magnetization process is likely to be most effective when the outer radius of the coils lies between 100% and 50% of the sample radius. A relatively large coil pair is necessary for samples with either a smaller aspect ratio or larger values of J c0. Two different regimes of flux penetration are found to be involved in the magnetization process. For a sufficiently small sample, the penetration field is determined by flux propagation from beneath the coil to the centre of the sample; for a sufficiently large sample, the definitive propagation route is from beneath the coil to the periphery of the sample. Effective split-coil magnetization occurs only in the former regime, and both penetration regimes are completely different from that involved in the solenoidal-coil magnetization process. © 2012 IOP Publishing Ltd.

Extracellular-matrix tethering regulates stem-cell fate.

To investigate how substrate properties influence stem-cell fate, we cultured single human epidermal stem cells on polydimethylsiloxane (PDMS) and polyacrylamide (PAAm) hydrogel surfaces, 0.1 kPa-2.3 MPa in stiffness, with a covalently attached collagen coating. Cell spreading and differentiation were unaffected by polydimethylsiloxane stiffness. However, cells on polyacrylamide of low elastic modulus (0.5 kPa) could not form stable focal adhesions and differentiated as a result of decreased activation of the extracellular-signal-related kinase (ERK)/mitogen-activated protein kinase (MAPK) signalling pathway. The differentiation of human mesenchymal stem cells was also unaffected by PDMS stiffness but regulated by the elastic modulus of PAAm. Dextran penetration measurements indicated that polyacrylamide substrates of low elastic modulus were more porous than stiff substrates, suggesting that the collagen anchoring points would be further apart. We then changed collagen crosslink concentration and used hydrogel-nanoparticle substrates to vary anchoring distance at constant substrate stiffness. Lower collagen anchoring density resulted in increased differentiation. We conclude that stem cells exert a mechanical force on collagen fibres and gauge the feedback to make cell-fate decisions.

Spray combustion characteristics of palm biodiesel

The potential of palm methyl esters (PME) as an alternative fuel for gas turbines is investigated using a swirl burner. The main air flow is preheated to 623 K, and a swirling spray flame is established at atmospheric pressure. The spray combustion characteristics of PME are compared to diesel and Jet-A1 fuel under the same burner power output of 6 kW. Investigation of the fuel atomizing characteristics using phase Doppler anemometry (PDA) shows that most droplets are distributed within the flame reaction zone region. PME droplets exhibit higher Sautermean diameter (SMD) values than baseline fuels, and thus higher droplet penetration length and longer evaporation timescales. The PME swirl flame presents a different visible flame reaction zone while combusting with low luminosity and produces no soot. NO x emissions per unit mass of fuel and per unit energy are reduced by using PME relative to those of conventional fuels. © 2012 Copyright Taylor and Francis Group, LLC.

Multi-hit armour characterisation of metal-composite bi-layers

The ballistic performance of equi-mass plates made from (i) stainless steel (SS); (ii) carbon fibre/epoxy (CF) laminate and (iii) a hybrid plate of both materials has been characterised for a spherical steel projectile. The hybrid plate was orientated with steel on the impact face (SSCF) and on the distal face (CFSS). The penetration velocity (V 50) was highest for the SS plate and lowest for the CF plate. A series of double impact tests were performed, with an initial velocity V I and a subsequent velocity V II at the same impact site. An interaction diagram in (V I,V II) space was constructed to delineate penetration from survival under both impacts. The degree of interaction between the two impact events was greater for the CFSS plate than for the SSCF plate, implying that the distal face has the major effect upon the degree of interaction.

Theoretical and experimental magnetization loss comparison between IBAD coils and RABiTS coils

This paper presents a comparative study of ac magnetization losses in two types of 2 G HTS racetrack coils. The magnetic substrate made by RABiTS is the main difference between the two types, because ferromagnetic loss caused by magnetic substrate is accounted into the total ac losses. IBAD and RABiTS tapes were successfully wound into racetrack shape with identical geometry. The measurements were carried out by using electromagnetic method with pick-up coils under a sinusoidally varying external magnetic field, with amplitudes up to 27 mT, ranging from 10 Hz to 100 Hz at a temperature of 77 K. The field was oriented perpendicularly to the surface of the tapes. Experimental measurements were validated by applying theoretical models and the results showed that the magnetization loss in the MAG RABiTS coil is always higher than that in the NON MAG coil due to the presence of the magnetic substrate, which increases the magnetic field penetration into the coil and causes higher magnetic flux density within the penetrated region. © 2002-2011 IEEE.

Measurement of the magnetic field inside the holes of a drilled bulk high-Tc superconductor

We use macroscopic holes drilled in a bulk YBCO superconductor to probe its magnetic properties in the volume of the sample. The sample is subjected to an AC magnetic flux with a density ranging from 30mT to 130mT and the flux in the superconductor is probed by miniature coils inserted in the holes. In a given hole, three different penetration regimes can be observed: (i) the shielded regime, where no magnetic flux threads the hole; (ii) the gradual penetration regime, where the waveform of the magnetic field has a clipped sine shape whose fundamental component scales with the applied field; and (iii) the flux concentration regime, where the waveform of the magnetic field is nearly a sine wave, with an amplitude exceeding that of the applied field by up to a factor of two. The distribution of the penetration regimes in the holes is compared with that of the magnetic flux density at the top and bottom surfaces of the sample, and is interpreted with the help of optical polarized light micrographs of these surfaces. We show that the measurement of the magnetic field inside the holes can be used as a local characterization of the bulk magnetic properties of the sample.

Magnetic shielding properties of a superconducting hollow cylinder containing slits: Modelling and experiment

This paper deals with the magnetic properties of bulk high temperature superconducting cylinders used as magnetic shields. We investigate, both numerically and experimentally, the magnetic properties of a hollow cylinder with two axial slits which cut the cylinder in equal halves. Finite element method modelling has been used with a three-dimensional geometry to help us in understanding how the superconducting currents flow in such a cut cylinder and therefore how the magnetic shielding properties are affected, depending on the magnetic field orientation. Modelling results show that the slits block the shielding current flow and act as an entrance channel for the magnetic flux lines. The contribution of the slits to the total flux density that enters the cylinder is studied through the angle formed between the applied field and the internal field. The modelled data agree nicely with magnetic shielding properties measured on a bulk Bi-2212 hollow cylinder at 77K. The results demonstrate that the magnetic flux penetration in such a geometry can be modelled successfully using only two parameters of the superconductor (constant J c and n value), which were determined from magnetic measurements on the plain cylinder. © 2012 IOP Publishing Ltd.

Numerical study of the shielding properties of macroscopic hybrid ferromagnetic/superconductor hollow cylinders

We study the magnetic shielding properties of hybrid ferromagnetic/ superconductor (F/S) structures consisting of two coaxial cylinders, with one of each material. We use an axisymmetric finite-element model in which the electrical properties of the superconducting tube are modeled by a nonlinear E-J power law with a magnetic-field-dependent critical current density whereas the magnetic properties of the ferromagnetic material take saturation into account. We study and compare the penetration of a uniform axial magnetic field in two cases: 1) a ferromagnetic tube placed inside a larger superconducting tube (Ferro-In configuration) and 2) a ferromagnetic tube placed outside the superconducting one (Ferro-Out configuration). In both cases, we assess how the ferromagnetic tube improves the shielding properties of the sole superconducting tube. The influence of the geometrical parameters of the ferromagnetic tube is also studied: It is shown that, upon an optimal choice of the geometrical parameters, the range of magnetic fields that are efficiently shielded by the high-temperature superconductor tube alone can be increased by a factor of up to 7 (2) in a Ferro-Out (Ferro-In) configuration. The optimal configuration uses a 1020 carbon steel with a thickness of 2 mm and a height that is half that of the superconducting cylinder (80 mm). © 2009 IEEE.

Magnetic shielding properties of high- Tc superconducting hollow cylinders: Model combining experimental data for axial and transverse magnetic field configurations

Magnetic shielding efficiency was measured on high- Tc superconducting hollow cylinders subjected to either an axial or a transverse magnetic field in a large range of field sweep rates, dBapp/dt. The behaviour of the superconductor was modelled in order to reproduce the main features of the field penetration curves by using a minimum number of free parameters suitable for both magnetic field orientations. The field penetration measurements were carried out on Pb-doped Bi-2223 tubes at 77K by applying linearly increasing magnetic fields with a constant sweep rate ranging between 10νTs-1 and 10mTs-1 for both directions of the applied magnetic field. The experimental curves of the internal field versus the applied field, Bin(Bapp), show that, at a given sweep rate, the magnetic field for which the penetration occurs, Blim, is lower for the transverse configuration than for the axial configuration. A power law dependence with large exponent, n′, is found between Blim and dBapp/dt. The values of n′ are nearly the same for both configurations. We show that the main features of the curves B in(Bapp) can be reproduced using a simple 2D model, based on the method of Brandt, involving a E(J) power law with an n-exponent and a field-dependent critical current density, Jc(B), (following the Kim model: Jc = Jc0(1+B/B1)-1). In particular, a linear relationship between the measured n′-exponents and the n-exponent of the E(J) power law is suggested by taking into account the field dependence of the critical current density. Differences between the axial and the transverse shielding properties can be simply attributed to demagnetizing fields. © 2009 IOP Publishing Ltd.

DC and AC Shielding properties of bulk high-tc

We have studied numerically and experimentally the magnetic flux penetration in high-Tc superconducting tube subjected to a uniform magnetic field parallel to its long axis. This study is carried in view of designing low-frequency magnetic shields by exploiting the diamagnetic properties of high-Tc superconducting ceramics. We have measured the field attenuation for applied magnetic fields in the frequency range 5 mHz-0.1 Hz by Hall probe measurements and at audio frequencies using a sensing coil. A simple 1D analysis using the Kim critical state model was found to be able to reproduce the experimental data satisfactorily. We have also determined the phase shift between the internal and the applied field both experimentally and numerically. Finally, we have studied the sweep rate dependence of the magnetic shielding properties, using data recorded either at several constant sweep rates dB /dt or at several AC fields of various amplitudes and frequencies. Both methods agree with each other and lead to a n-value of the E ∼ Jn law equal to ∼40 at 77 K. © 2009 IEEE.

Seafloor-riser interaction model

Fatigue stresses associated with extreme storms, vessel movements, and vortex-induced vibrations are critical to the performance of steel catenary risers. The critical location for fatigue damage often occurs within the touchdown zone, where cyclic interaction of the riser with the seabed occurs. Developing a model for seabed stiffness requires characterization of a number of complex nonlinear processes including trench formation, nonlinear soil stiffness, soil suction, and breakaway of the riser from the seafloor. The analytical framework utilized in this research considers the riser-seafloor interaction problem in terms of a pipe resting on a bed of springs, the stiffness characteristics of which are described by nonlinear load-deflection (P-y) curves. The P-y model allows for first penetration and uplift, as well as repenetration and small range motions within the bounding loop defined by extreme loading. The backbone curve is constructed from knowledge of the soil strength, the rate of strength increase with depth, trench width, and two additional parameters, while three parameters are necessary for the cyclic response. © ASCE 2009.

The effect of shear strength on the ballistic response of laminated composite plates

The ballistic performance of clamped circular carbon fibre reinforced polymer (CFRP) and Ultra High Molecular Weight Polyethylene (UHMWPE) fibre composite plates of equal areal mass and 0/90 lay-up were measured and compared with that of monolithic 304 stainless steel plates. The effect of matrix shear strength upon the dynamic response was explored by testing: (i) CFRP plates with both a cured and uncured matrix and (ii) UHMWPE laminates with identical fibres but with two matrices of different shear strength. The response of these plates when subjected to mid-span, normal impact by a steel ball was measured via a dynamic high speed shadow moiré technique. Travelling hinges emanate from the impact location and travel towards the supports. The anisotropic nature of the composite plate results in the hinges travelling fastest along the fibre directions and this results in square-shaped moiré fringes in the 0/90 plates. Projectile penetration of the UHMWPE and the uncured CFRP plates occurs in a progressive manner, such that the number of failed plies increases with increasing velocity. The cured CFRP plate, of high matrix shear strength, fails by cone-crack formation at low velocities, and at higher velocities by a combination of cone-crack formation and communition of plies beneath the projectile. On an equal areal mass basis, the low shear strength UHMWPE plate has the highest ballistic limit followed by the high matrix shear strength UHMWPE plate, the uncured CFRP, the steel plate and finally the cured CFRP plate. We demonstrate that the high shear strength UHMWPE plate exhibits Cunniff-type ballistic limit scaling. However, the observed Cunniff velocity is significantly lower than that estimated from the laminate properties. The data presented here reveals that the Cunniff velocity is limited in its ability to characterise the ballistic performance of fibre composite plates as this velocity is independent of the shear properties of the composites: the ballistic limit of fibre composite plates increases with decreasing matrix shear strength for both CFRP and UHMWPE plates. © 2013 Elsevier Masson SAS. All rights reserved.

Sensitivity analysis and optimization of the nuclear fuel cycle

A sensitivity study has been conducted to assess the robustness of the conclusions presented in the MIT Fuel Cycle Study. The Once Through Cycle (OTC) is considered as the base-line case, while advanced technologies with fuel recycling characterize the alternative fuel cycles. The options include limited recycling in LWRs and full recycling in fast reactors and in high conversion LWRs. Fast reactor technologies studied include both oxide and metal fueled reactors. The analysis allowed optimization of the fast reactor conversion ratio with respect to desired fuel cycle performance characteristics. The following parameters were found to significantly affect the performance of recycling technologies and their penetration over time: Capacity Factors of the fuel cycle facilities, Spent Fuel Cooling Time, Thermal Reprocessing Introduction Date, and incore and Out-of-core TRU Inventory Requirements for recycling technology. An optimization scheme of the nuclear fuel cycle is proposed. Optimization criteria and metrics of interest for different stakeholders in the fuel cycle (economics, waste management, environmental impact, etc.) are utilized for two different optimization techniques (linear and stochastic). Preliminary results covering single and multi-variable and single and multi-objective optimization demonstrate the viability of the optimization scheme.

Short-term cytotoxic and inflammatory responses of human monocytes to stainless steel fibre networks

The aim of the current work was to examine the human monocyte response to 444 ferritic stainless steel fibre networks. 316L austenitic fibre networks, of the same fibre volume fraction, were used as control surfaces. Fluorescence and scanning electron microscopies suggest that the cells exhibited a good degree of attachment and penetration throughout both networks. Lactate Dehydrogenase (LDH) and TNF-α releases were used as indicators of cytotoxicity and inflammatory responses respectively. LDH release indicated similar levels of monocyte viability when in contact with the 444 and 316L fibre networks. Both networks elicited a low level secretion of TNF-α, which was significantly lower than that of the positive control wells containing zymosan. Collectively, the results suggest that 444 ferritic and 316L austenitic networks induced similar cytotoxic and inflammatory responses from human monocytes. © 2012 Materials Research Society.

Inclusive design and the bottom line: How can its value be proven to decision makers?

Designing technology products that embrace the needs and capabilities of heterogeneous users leads not only to increased customer satisfaction and enhanced corporate social responsibility, but also better market penetration. Yet, achieving inclusion in today's pressured and fast-moving markets is not straight-forward. For a time, inaccessible and unusable design was solely seen as the fault of designers and a whole line of research was dedicated to pinpointing their frailties. More recently, it has become progressively more recognised that it is not necessarily designers' lack of awareness, or unwillingness, that results in sub-optimal design, but rather there are multi-faceted organisational factors at play that seldom provide an adequate environment in which inclusive products could be designed. Through literature review, a detailed audit of inclusivity practice in a large global company and ongoing research regarding quantification of cost-effectiveness of inclusive design, this paper discusses the overarching operational problems that prevent organisations from developing optimally inclusive products and offers best-practice principles for the future. © 2013 Springer-Verlag Berlin Heidelberg.