Magneto-transport study of Nb-doped Bi/Pb2223 superconductor

The magneto-transport properties of Bi1.5Pb0.4Nb0.1Sr2Ca2Cu 3O10-x polycrystalline, superconducting ceramic are reported. The material was found to be chemically homogeneous and partially textured. The mixed state properties were investigated by measuring the electrical resistivity, longitudinal and transverse (Nernst effect) thermoelectric power, and thermal conductivity. The magnetization and AC susceptibility measurements were also performed. The variation of these characteristics for magnetic fields up to 5 T are discussed and compared to those of the zero field case. The transport entropy and thermal Hall angle are extracted and quantitatively compared to previously reported data of closely related systems. © 2003 Elsevier Science B.V. All rights reserved.

Intragranular and intergranular behaviour of multifilamentary Bi-2223/Ag tapes

This communication aims at reporting the superconducting properties of Bi-2223/Ag tapes determined by using various measuring techniques. First, the original samples have been characterized by electrical resistance, AC susceptibility, and DC magnetization. The transport (intergranular) critical current vs. magnetic field was also determined at T = 77 K using pulsed currents up to 40 A. Next, the same combination of experiments was performed on bent tapes in order to bring out relevant information concerning the strength of the intergranular coupling. The results show that intergranular and intragranular currents differ by at least one order of magnitude. Finally, additional magnetic measurements were carried out in order to determine the anisotropy ratio Jc ab/Jc c, which was found to lie around 30. © 2002 Elsevier Science B.V. All rights reserved.

Frames, biases, and rational decision-making in the human brain.

Human choices are remarkably susceptible to the manner in which options are presented. This so-called "framing effect" represents a striking violation of standard economic accounts of human rationality, although its underlying neurobiology is not understood. We found that the framing effect was specifically associated with amygdala activity, suggesting a key role for an emotional system in mediating decision biases. Moreover, across individuals, orbital and medial prefrontal cortex activity predicted a reduced susceptibility to the framing effect. This finding highlights the importance of incorporating emotional processes within models of human choice and suggests how the brain may modulate the effect of these biasing influences to approximate rationality.

Vortex migration caused by travelling magnetic wave in a 2 in. diameter YBa2Cu3O7-δ thin film

We provide experimental evidence for a vortex migration phenomenon in YBa2Cu3O7-δ (YBCO) thin film caused by travelling magnetic wave. The experiment is carried out on a 2 in. diameter YBCO thin film with a circular-type magnetic flux pump. We found that the travelling wave helps the vortices migrate into the centre of the sample: after the zero-field cooling process, the increase of the flux density in the centre is four times larger than the amplitude of the travelling wave. The reason for this massive vortex migration is probably due to the magnetic stress variation caused by the travelling wave: the magnetic stress increases locally in the crest region while decreases locally in the trough region, which could help the vortices to move locally. A comparison shows that the magnetization by standing wave can be easily predicted by Bean's model while travelling wave causes vortex migration generally much larger than the prediction of Bean's model. It is possible that travelling magnetic wave can be an effective way to magnetize a type II superconductor in considering this unusual vortex dynamics. © 2013 AIP Publishing LLC.

Optimizing the energy offset between dye and hole-transporting material in solid-state dye-sensitized solar cells

The power-conversion efficiency of solid-state dye-sensitized solar cells can be optimized by reducing the energy offset between the highest occupied molecular orbital (HOMO) levels of dye and hole-transporting material (HTM) to minimize the loss-in-potential. Here, we report a study of three novel HTMs with HOMO levels slightly above and below the one of the commonly used HTM 2,2′,7,7′- tetrakis(N,N-di-p-methoxyphenylamino)-9,9′- spirobifluorene (spiro-OMeTAD) to systematically explore this possibility. Using transient absorption spectroscopy and employing the ruthenium based dye Z907 as sensitizer, it is shown that, despite one new HTM showing a 100% hole-transfer yield, all devices based on the new HTMs performed worse than those incorporating spiro-OMeTAD. We further demonstrate that the design of the HTM has an additional impact on the electronic density of states present at the TiO2 electrode surface and hence influences not only hole- but also electron-transfer from the sensitizer. These results provide insight into the complex influence of the HTM on charge transfer and provide guidance for the molecular design of new materials. © 2013 American Chemical Society.

Multispacecraft refueling optimization considering the J2 perturbation and window constraints

The optimization of a near-circular low-Earth-orbit multispacecraft refueling problem is studied. The refueling sequence, service time, and orbital transfer time are used as design variables, whereas the mean mission completion time and mean propellant consumed by orbital maneuvers are used as design objectives. The J2 term of the Earth's nonspherical gravity perturbation and the constraints of rendezvous time windows are taken into account. A hybridencoding genetic algorithm, which uses normal fitness assignment to find the minimum mean propellant-cost solution and fitness assignment based on the concept of Pareto-optimality to find multi-objective optimal solutions, is presented. The proposed approach is demonstrated for a typical multispacecraft refueling problem. The results show that the proposed approach is effective, and that the J2 perturbation and the time-window constraints have considerable influences on the optimization results. For the problems in which the J2 perturbation is not accounted for, the optimal refueling order can be simply determined as a sequential order or as the order only based on orbitalplane differences. In contrast, for the problems that do consider the J2 perturbation, the optimal solutions obtained have a variety of refueling orders and use the drift of nodes effectively to reduce the propellant cost for eliminating orbital-plane differences. © 2013 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Hermetically-coated superparamagnetic Fe2O3 particles with SiO2 nanofilms

Magnetic nanoparticles are frequently coated with SiO2to improve their functionality and bio-compatibility in a range of biomedical and polymer nanocomposile applications. In this paper, a scalable flame aerosol technology is used to produce highly dispersible, superparamagnetic iron oxide nanoparticles hermetically coaled with silica to retain full magnetization performance. Iron oxide particles were produced by flame spray pyrolysis (FSP) of iron acelylacetonale in xylene/acetonitrile solutions, and the resulting aerosol was in situ coaled with SiO2 by oxidation of swirling hexamethlydisiloxane vapor. The process allows independent control of the core Fe2O3, particle properties and the thickness of their silica coaling film. This ensures that the non-magnetic SiO2 layer can be closely controlled and minimized. The optimal SiO2 content for complete (hermetic) encapsulation of the magnetic core particles was determined by isopropanol chemisorption. The magnetization of Fe2O3 coated with about 2 nm thin SiO2 layers was nearly identical lo that of uncoated, pure Fe2O3 nanoparlicles.

Hermetically coated superparamagnetic Fe2O3 particles with SiO2 nanofilms

Magnetic nanoparticles are frequently coated with SiO2 to improve their functionality and biocom-patibility in a range of biomedical and polymer nanocomposite applications. In this paper, a scalable flame aerosol technology is used to produce highly dispersible, superparamagnetic iron oxide nanoparticles hermetically coated with silica to retain full magnetization performance. Iron oxide particles were produced by flame spray pyrolysis of iron acetylacetonate in xylene/acetonitrile solutions and the resulting aerosol was in situ coated with silicon dioxide by oxidation of swirling hexamethlydisiloxane vapor. The process allows independent control of the core Fe2O3 (maghemite) particle properties and the thickness of their silica coating film. This ensures that the nonmagnetic SiO2 layer can be closely controlled and minimized. The optimal SiO2 content for complete (hermetic) encapsulation of the magnetic core particles was determined by isopropanol chemisorption. The magnetization of Fe 2O3 coated with about 2 nm thin SiO2 layers was nearly identical to that of uncoated, pure Fe2O3 nanoparticles. © 2009 American Chemical Society.

Effect of size, composition, and morphology on magnetic performance: First-order reversal curves evaluation of iron oxide nanoparticles

© 2014 AIP Publishing LLC. Superparamagnetic nanoparticles are employed in a broad range of applications that demand detailed magnetic characterization for superior performance, e.g., in drug delivery or cancer treatment. Magnetic hysteresis measurements provide information on saturation magnetization and coercive force for bulk material but can be equivocal for particles having a broad size distribution. Here, first-order reversal curves (FORCs) are used to evaluate the effective magnetic particle size and interaction between equally sized magnetic iron oxide (Fe2O3) nanoparticles with three different morphologies: (i) pure Fe2O3, (ii) Janus-like, and (iii) core/shell Fe2O3/SiO2synthesized using flame technology. By characterizing the distribution in coercive force and interaction field from the FORC diagrams, we find that the presence of SiO2in the core/shell structures significantly reduces the average coercive force in comparison to the Janus-like Fe2O3/SiO2and pure Fe2O3particles. This is attributed to the reduction in the dipolar interaction between particles, which in turn reduces the effective magnetic particle size. Hence, FORC analysis allows for a finer distinction between equally sized Fe2O3particles with similar magnetic hysteresis curves that can significantly influence the final nanoparticle performance.

Stable dynamic walking over uneven terrain

We propose a constructive control design for stabilization of non-periodic trajectories of underactuated robots. An important example of such a system is an underactuated "dynamic walking" biped robot traversing rough or uneven terrain. The stabilization problem is inherently challenging due to the nonlinearity, open-loop instability, hybrid (impact) dynamics, and target motions which are not known in advance. The proposed technique is to compute a transverse linearization about the desired motion: a linear impulsive system which locally represents "transversal" dynamics about a target trajectory. This system is then exponentially stabilized using a modified receding-horizon control design, providing exponential orbital stability of the target trajectory of the original nonlinear system. The proposed method is experimentally verified using a compass-gait walker: a two-degree-of-freedom biped with hip actuation but pointed stilt-like feet. The technique is, however, very general and can be applied to a wide variety of hybrid nonlinear systems. © The Author(s) 2011.

Magnetic characterisation of large grain, bulk Y-Ba-Cu-O superconductor-soft ferromagnetic alloy hybrid structures

Large grain, bulk Y-Ba-Cu-O (YBCO) high temperature superconductors (HTS) have significant potential for use in a variety of practical applications that incorporate powerful quasi-permanent magnets. In the present work, we investigate how the trapped field of such magnets can be improved by combining bulk YBCO with a soft FeNi, ferromagnetic alloy. This involves machining the alloy into components of various shapes, such as cylinders and rings, which are attached subsequently to the top surface of a solid, bulk HTS cylinder. The effect of these modifications on the magnetic hysteresis curve and trapped field of the bulk superconductor at 77 K are then studied using pick-up coil and Hall probe measurements. The experimental data are compared to finite element modelling of the magnetic flux distribution using Campbell's algorithm. Initially we establish the validity of the technique involving pick-up coils wrapped around the bulk superconductor to obtain its magnetic hysteresis curve in a non-destructive way and highlight the difference between the measured signal and the true magnetization of the sample. We then consider the properties of hybrid ferromagnet/superconductor (F/S) structures. Hall probe measurements, together with the results of the model, establish that flux lines curve outwards through the ferromagnet, which acts, effectively, like a magnetic short circuit. Magnetic hysteresis curves show that the effects of the superconductor and the ferromagnet simply add when the ferromagnet is saturated fully by the applied field. The trapped field of the hybrid structure is always larger than that of the superconductor alone below this saturation level, and especially when the applied field is removed. The results of the study show further that the beneficial effects on the trapped field are enhanced when the ferromagnet covers the entire surface of the superconductor for different ferromagnetic components of various shapes and fixed volume. © 2014 Elsevier B.V. All rights reserved.

Quantitative structure-property relationships for octanol-air partition coefficients of polychlorinated naphthalenes, chlorobenzenes and p,p '-DDT

The octanol-air partition coefficient (K-OA) is a key descriptor of chemicals partitioning between the atmosphere and environmental organic phases. Quantitative structure-property relationships (QSPR) are necessary to model and predict KOA from molecular structures. Based on 12 quantum chemical descriptors computed by the PM3 Hamiltonian, using partial least squares (PLS) analysis, a QSPR model for logarithms of K-OA to base 10 (log K-OA) for polychlorinated naphthalenes (PCNs), chlorobenzenes and p,p'-DDT was obtained. The cross-validated Q(cum)(2) value of the model is 0.973, indicating a good predictive ability of the model. The main factors governing log K-OA of the PCNs, chlorobenzenes, and p,p'-DDT are, in order of decreasing importance, molecular size and molecular ability of donating/accepting electrons to participate in intermolecular interactions. The intermolecular dispersive interactions play a leading role in governing log K-OA. The more chlorines in PCN and chlorobenzene molecules, the greater the log K-OA values. Increasing E-LUMO (the energy of the lowest unoccupied molecular orbital) of the molecules leads to decreasing log K-OA values, implying possible intermolecular interactions between the molecules under study and octanol molecules. (C) 2002 Elsevier Science Ltd. All rights reserved.

Quantitative relationships between molecular structures, environmental temperatures and octanol-air partition coefficients of PCDD/Fs

A concise quantitative model that incorporates information on both environmental temperature M and molecular structures, for logarithm of octanol-air partition coefficient (K-OA) to base 10 (logK(OA)) of PCDDs, was developed. Partial least squares (PLS) analysis together with 14 quantum chemical descriptors were used to develop the quantitative relationships between structures, environmental temperatures and properties (QRSETP) model. It has been validated that the obtained QRSETP model can be used to predict logK(OA) of other PCDDs. Molecular size, environmental temperature (T), q(+) (the most positive net atomic charge on hydrogen or chlorine atoms in PCDD molecules) and E-LUMO (the energy of the lowest unoccupied molecular orbital) are main factors governing logK(OA) of PCDD/Fs under study. The intermolecular dispersive interactions and thus the size of the molecules play a leading role in governing logK(OA). The more chlorines in PCDD molecules, the greater the logK(OA) values. Increasing E-LUMO values of the molecules leads to decreasing logK(OA) values, implying possible intermolecular interactions between the molecules under study and octanol molecules. Greater q(+) values results in greater intermolecular electrostatic repulsive interactions between PCDD and octanol molecules and smaller logK(OA) values. (C) 2002 Elsevier Science B.V. All rights reserved.

Quantitative structure-property relationships for octanol-air partition coefficients of polychlorinated biphenyls

Based on nine quantum chemical descriptors computed by PM3 Hamiltonian, using partial least squares analysis, a significant quantitative structure-property relationship for the logarithm of octanol-air partition coefficients (log K-OA) of polychlorinated biphenyls (PCBs) was obtained. The cross-validated Q(cum)(2) value of the model is 0.962, indicating a good predictive ability. The intermolecular dispersive interactions and thus the size of the PCB molecules play a key role in governing log K-OA. The greater the size of PCB molecules, the greater the log K-OA values. Increasing E-LUMO (the energy of the lowest unoccupied molecular orbital) values of the PCBs leads to decreasing log K-OA values, indicating possible interactions between PCB and octanol molecules. Increasing Q(Cl)(+) (the most positive net atomic charges on a chlorine atom) and Q(C)(-) (the largest negative net atomic charge on a carbon atom) values of PCBs results in decreasing log K-OA values, implying possible intermolecular electrostatic interactions between octanol and PCB molecules. (C) 2002 Elsevier Science Ltd. All rights reserved.

Quantitative structure-property relationships (QSPRs) on direct photolysis of PCDDs

By the use of partial least squares (PLS) method and 27 quantum chemical descriptors computed by PM3 Hamiltonian, a statistically significant QSPR were obtained for direct photolysis quantum yields (Y) of selected Polychlorinated dibenzo-p-dioxins (PCDDs). The QSPR can be used for prediction. The direct photolysis quantum yields of the PCDDs are dependent on the number of chlorine atoms bonded with the parent structures, the character of the carbon-oxygen bonds, and molecular polarity. Increasing bulkness and polarity of PCDDs lead to decrease of log Y values. Increasing the frontier molecular orbital energies (E-lumo and E-homo) and heat of formation (HOF) values leads to increase of log Y values. (C) 2001 Elsevier Science Ltd. All rights reserved.