In-field Behavior Research Articles

Comparison of the Field Trapping Ability of MgB2 and Hybrid Disc-Shaped Layouts.

Superconductors have revolutionized magnet technology, surpassing the limitations of traditional coils and permanent magnets. This work experimentally investigates the field-trapping ability of a MgB2 disc at various temperatures and proposes new hybrid (MgB2-soft iron) configurations using a numerical approach based on the vector potential (A→) formulation. The experimental characterization consists in measurements of trapped magnetic flux density carried out using cryogenic Hall probes located at different radial positions over the MgB2 sample, after a field cooling (FC) process and the subsequent removal of the applied field. Measurements were performed also as a function of the distance from the disc surface. The numerical modelling of the superconductor required the evaluation of the critical current density dependence on the magnetic flux density (Jc(B)) obtained through an iterative procedure whose output were successfully validated by the comparison between experimental and computed data. The numerical model, upgraded to also describe the in-field behavior of ARMCO soft iron, was then employed to predict the field-trapping ability of hybrid layouts of different shapes. The most promising results were achieved by assuming a hollow superconducting disc filled with a ferromagnetic (FM) cylinder. With such a geometry, optimizing the radius of the FM cylinder while the external dimensions of the superconducting disc are kept unchanged, an improvement of more than 30% is predicted with respect to the full superconducting disc, assuming a working temperature of 20 K.

Magnetic structure and highly unusual in-field behaviour of D-type erbium disilicate

Magnetic structure and highly unusual in-field behaviour of <i>D</i>-type erbium disilicate

The Effect of Aliovalent Substitution on Magnetic Properties of PolyCrystalline Ca/K-1144

Among IBSC superconductors, the 1144 family ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">AAE</i> Fe4As4 with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A</i> =alkali metal, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">AE</i> =alkaline-earth metal), has attracted considerable interest in recent years because of their propensity to form lattice defects that positively influence the flux pinning properties. Extensive research is underway to optimize this class of materials for the low-temperature high-field regime, both in the form of single crystal and polycrystalline powder. The latter is of particular interest because the 1144 material has been shown to be suitable for wire production through the easy and well-assessed Powder In Tube (PIT) process. <p xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">In our recent experiments, it has been shown that the 1144 structure can be tailored to obtain a doped compound with a different chemical formula (<i>A</i>_x<i>AE</i>_1-x)(<i>AE</i>_y<i>A</i>_1-y)Fe₄As₄, that is characterized by unaltered critical temperature values despite the high level of substitution up to 15 at.%. In order to unveil the influence of the double substitution on the grain boundary and pinning properties of doped samples, we recently started an extensive characterization campaign whose preliminary results are presented here. Both structural and morphological properties of the compound are not affected by the simultaneous doping with 10 at.% Na and 5 at.% Ba, as revealed by XRD and SEM analyses. On the contrary, the study of magnetic properties shows that although there is no improvement in transport properties, the aliovalent substitution induces a clear change in the in-field behavior which deserves further investigations.

Non-Invasive Techniques Reveal Heifer Response to Fescue Endophyte Type in Grazing Studies.

Cattle grazing tall fescue (Schedonorus arundinaceous) infected with wild-type endophytes (WE) leads to a syndrome commonly known as fescue toxicosis. Replacing WE tall fescue with a novel endophyte-infected (NE) tall fescue can mitigate this problem but adoption of this technology has been limited. This study measured and determined the physiological and behavioral responses of heifers that grazed either WE or NE tall fescue, utilizing relatively non-invasive techniques including hair cortisol, thermography (for extremity temperatures), small loggers for intravaginal temperature, and remote observation of in-field behavior. Heifers that grazed WE had greater (p < 0.0001) hair cortisol levels, lower extremity temperatures (p ≤ 0.0075), and 0.3-0.9 °C greater (p ≤ 0.02) intravaginal temperatures (particularly during the daytime) than heifers that grazed NE. From 1200 h-1700 h each day, heifers on WE pastures spent 1.5 more (p = 0.0003) hours standing up and 0.9 fewer (p = 0.0402) hours lying down than heifers on NE pastures. Differences (p = 0.0160) in ADG were small (0.1 kg d-1) and were only observed in the first year of these 8-week studies. However, even in the mild environment of the study site, grazing NE tall fescue provided clear welfare benefits as evidenced by heifer behavioral changes, temperature differentials, and hair cortisol levels. This study underscores the potential utility of non-invasive techniques, such as thermographic imaging and hair cortisol analysis, for evaluating animal responses to stress in extensive grazing systems.

Dynamic Performance Detection of CFRP Composite Pipes based on Quasi-Distributed Optical Fiber Sensing Techniques

For the high strength, corrosion resistance, and good stability, carbon fiber–reinforced polymer (CFRP) composites have been made into pipes to transfer gasses and oils in subsea environment. Structural performance of CFRP composite pipes is particularly important to sustain the regular operation of the delivery system. To obtain the in-field behavior of the CFRP composite pipes, quasi-distributed optical fiber sensing techniques are developed based on the multiple configuration of fiber Bragg grating (FBG) sensing elements. Theoretical investigation on the dynamic response of the pipes is performed. Experiments on cantilever CFRP pipes with surface-attached FBGs in series and packaged FBG sensors have been conducted to check the feasibility and effectiveness of the proposed sensing technique. Results validate the good measurement performance of the proposed sensors and the accuracy of the vibration analysis. The study can be adopted to instruct the establishment of the structural health monitoring system of CFRP composite pipes and assess the safety operation state of the pipe systems.

Field-induced magnetic states in geometrically frustrated SrEr2O4

We report an unusual in-field behaviour of SrEr_22O_44 for a magnetic field applied along two high-symmetry directions, the a and c axes. This geometrically frustrated magnet hosts two crystallographically inequivalent Er ions, Er1 and Er2, that are both located on triangular zigzag ladders, but only one site, Er1, forms a long-range magnetic order at low temperatures in a zero field. We follow the sequence of peculiar field induced states in SrEr_22O_44 with detailed single-crystal magnetisation and neutron diffraction experiments. On application of an external field along the cc axis, the long-range antiferromagnetic order of the Er1 ions is rapidly destroyed and replaced, in fields between 2 and 5 kOe, by a state with shorter-range correlations. The change in correlation length coincides with a fast increase in magnetisation during the metamagnetic transition above which a long-range order is reestablished and maintained into the high fields. The high-field ferromagnet-like order is characterised by significantly different magnetic moments on the two Er sites, with the Er1 site dominating the magnetisation process. For the field applied parallel to the a axis, in the field range of 4 to 12 kOe, the planes of diffuse magnetic scattering observed in zero field due to the one-dimensional correlations between the Er2 moments are replaced by much more localised but still diffuse features corresponding to the establishment of an up-up-down structure associated with a one-third magnetisation plateau. Above 14 kOe, a ferromagnet-like high-field order is induced following another phase transition. For this direction of the field, the Er2 moments dictate the succession of transitions while the Er1 moments remain significantly less polarised. A complete field polarisation of both Er sites is not achieved even at 50~kOe for either field direction, reflecting the strongly anisotropic nature of magnetisation process in SrEr_22O_44.

In-field critical current performance of 4.0 μm thick film REBCO conductor with Hf addition at 4.2 K and fields up to 31.2 T

We present results on the in-field critical current (Ic) performance of 4.0 μm thick REBCO film with 15% Hf addition with fields up to 31.2 T and field orientations in the B║ab plane and B║c axis. Unlike the behavior at B║c, the critical current at B║ab is only very weakly dependent on field, decreasing from self-field to 31.2 T by only 22%, i.e. from the self-field value of ∼7700 A/4 mm width to ∼6300 and 5812 A/4 mm width at 14 and 30 T, respectively. These values are remarkably 3 and 5.7x higher than the corresponding critical currents at B║c. The in-field behavior of the present 15% Hf sample at field orientation B║c axis is nearly identical to the previously reported record values found in 4.3 and 4.6 μm thick 15% Zr samples in terms of critical current density. In contrast to the pinning force behavior in the B║c orientation, which saturates to a constant value of 1.7 TN m−3 above ∼5–6 T, the pinning force in the B║ab orientation increases near-linearly, reaching a remarkable value of over 11.5 TN m−3 at 31.2 T. These results demonstrate the potential of thick REBCO conductors at 4.2 K for high field and energy density applications, in particular where the magnetic field is contained near the ab-plane.

Polymer-assisted surface decoration for critical current enhancement in YBa2Cu3O7−x films

In this study, chemically decorated surfaces are employed as tools for Artificial Pinning Centres (APC) introduction in superconducting YBa2Cu3O7−x (YBCO) films. Self-assembled oxide nanostructures are grown on crystalline substrates via a very versatile and low-cost chemical technique called Polymer Assisted Deposition (PAD). Such decorated templates are used, in a second step, as substrates for YBCO film growth via Metal Organic Decomposition (MOD) or Pulsed Laser Deposition (PLD). The aim of the structures is to produce in the superconducting matrix strain and/or defects that should act as APCs and therefore enhance the transport properties of the samples. The oxides selected for the decoration are commonly used for the introduction of artificial pinning centres in YBCO: BaZrO3 and ZrO2. The decorated surfaces are analyzed via Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). YBCO films have been characterized via SEM, X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM), DC resistivity and critical current measurements. The results show that the nanostructures are stable and that they can efficiently introduce strain and stacking faults in the film. This causes an increase in the value of the critical current density Jc and better in-field behaviour in all the investigated field range, compared to the analogous film grown on a standard substrate, especially for chemically derived YBCO. Also Jc angular dependence measurements, Jc(θ), show an isotropic enhancement of the critical current for every angle of application of the field.

Differential degradation patterns of photovoltaic backsheets at the array level

There are relatively few field studies on the degradation of non-fluoropolymer-based backsheets, and understanding their in-field behavior is critical for further development of such products. In this study, backsheet degradation of modules with one of these new types of backsheets (polyethylene naphthalate (PEN)-based) was documented at a four-year old utility-scale array located in Maryland (USA). Visual inspection, colorimetry, glossimetry, and Fourier-transform infrared spectroscopy (FTIR) revealed highly varied properties depending on module position within the array. Specifically, modules near the edge of the array and with higher mounting elevations underwent greater amounts of backsheet degradation, as indicated by yellowing and gloss-loss. The reason for these unique degradation patterns were differential backside exposure conditions, especially of ultraviolet light. This was strongly influenced by the array design, including array structural and environmental factors, such as module spacing and ground cover, respectively. Within the array, no clear link between backsheet degradation and module output or safety has been identified. However, such a relationship may be expected to become more pronounced with time, affecting system lifetime and ultimately the levelized cost of electricity (LCOE). The observed phenomena have implications for both backsheet product development and array design, especially for modules that utilize newer classes of non-fluoropolymer-based backsheets which are typically more susceptible to environmental degradation.

Simulating the In-Field AC and DC Performance of High-Temperature Superconducting Coils

In this paper, the authors investigate numerically the in-field behavior of high-temperature superconducting (HTS) coils and a method to potentially improve their performance using ferromagnetic material as a flux diverter. The ability to accurately predict the electromagnetic behavior of superconductors in complex geometries and electromagnetic environments is crucial to the design of commercially viable superconductor-based electrical devices, such as power transmission cables, superconducting fault current limiters, transformers, and motors and generators. The analysis is carried out using a 2-D axisymmetric model of a circular pancake coil based on the H-formulation and implemented in Comsol Multiphysics 4.3a. We explore the use of flux diverters to improve an HTS coil's performance with respect to its dc (maximum allowable/critical current) and ac (ac loss) characteristics, for various background magnetic fields. It is found that while flux diverters can improve the ac properties of coils, they can be detrimental to the dc properties in this particular configuration.

Evaluation of the predictive validity of the Behavioural Assessment for Re-homing K9's (B.A.R.K.) protocol and owner satisfaction with adopted dogs

It is common practice for animal shelters and rescue organisations to conduct behaviour assessments on the dogs in their care. The information obtained is used to identify dogs suitable for re-homing and also assist with matching dogs to appropriate homes. Although the aim of these assessments is to provide a snapshot of the behavioural characteristics of individual dogs, research to determine whether such tools are effective and accurate in predicting the behaviour of dogs post adoption is currently lacking. In the present study, we investigated the predictive validity of a standardised protocol called the Behavioural Assessment for Re-homing K9's (B.A.R.K.). We used the B.A.R.K. protocol to assess 74 dogs housed in an animal shelter, prior to their adoption. All dogs were at least 1 year of age (mean=2.86 years, SD=2.02). New owners of these dogs took part in a post adoption survey 2–8 months (mean=4) after they adopted their dog. The survey aimed to establish the degree to which the behavioural tendencies identified by the B.A.R.K. protocol carried through to the adoptive home. The predictive validity of the B.A.R.K. protocol was relatively poor. Multiple regression analyses revealed that fear, measured by the B.A.R.K. protocol, significantly predicted ‘fearful/inappropriate toileting’ behaviours post adoption (β=0.36, P<0.05), as did anxiety (β=−0.31, P<0.05). However problem behaviours more generally and aggression post adoption were not predicted by the B.A.R.K. protocol. Almost 25% of adopters reported that their new dog had ‘growled, snapped at, or attempted to bite a person’ and nearly 75% indicated that their dog exhibited behaviour they would change if they could. Despite this, just over half (56.8%) of the new owners said they were very satisfied with the behaviour of their newly adopted dog and 71.2% said their adopted dog had met their expectations. Our results suggest that additional research is urgently needed to evaluate the predictive validity of in-field behaviour assessments and whether a more holistic, or alternative, approach to assessing shelter dog behaviour, such as longer-term foster care programmes, is required to safeguard the welfare of dogs in the shelter system and the community at large.

Peculiarities of Giant Magnetocaloric Effect in Ni50Mn35In15 Alloys in the Vicinity of Martensitic Transition

Adiabatic temperature change, resulting from MCE, is a complex effect depending on in-field behavior of both lattice and magnetic subsystem of the sample. For studying MCE, the understanding of their interplay is crucial. Comparing ΔTad in different fields (e.g. below, above and far above saturation field) it should be possible to derive contributions from lattice and magnetic subsystems. In this present work we present our study of the MCE in Ni50Mn35In15 Heusler alloy in the vicinity of the magnetostructural transition in 1.6 T and 14 T field.

Magnetic response of polycrystalline YBaCo4O7+δ synthesized through the physical and chemical route: The role of phase inhomogeneities

Polycrystalline YBaCo4O7+δ samples were obtained through a standard solid state reaction, and their structural, morphological, electrical, and magnetic properties are carefully studied. The X-ray powder diffraction (XRD) patterns showed reflections of a pure hexagonal structure (space group P63mc) with lattice parameters being very close to those reported in the literature. Although XRD analysis showed that the main phase present is 114, the presence of secondary phases could not be ruled out based solely on the XRD characterization. Indeed, sensitive SQUID magnetic measurements showed that the samples were affected by very small quantities of the 112 phase (YBaCo2O5.5), which typically manifests itself through a conspicuous increase in the magnetization at~300K. The results achieved corroborated the predictions concerning the difficulty of stabilizing the 114 phase when synthesized via the standard solid-state reaction. With this in mind, we next attempted to obtain the compound with improved phase purity. In so doing, the YBaCo4O7+δ compound was synthesized through a wet chemistry method based on a citrates route. The XRD patterns recorded for these samples revealed well-defined peaks corresponding to a pure hexagonal structure. More interestingly, SQUID measurements show no sign of features in the M(T) curve at temperatures as low as~80K. This result was consistent with the magnetic behavior observed in YBaCo4O7+δ single-crystals. At temperatures below~80K, a clear feature was observed which seemed to correlate with a transition into an antiferromagnetic state. Isothermal magnetization recorded at 70K showed that field-induced effects manifested themselves through the appearance of a ferromagnetic-like component. This ferromagnetic component may arise from spin canting of the underlying antiferromagnetic state or through field-induced structural transition (at least at local scale). Although a definitive interpretation of the in-field behavior from magnetization data alone is difficult because of the unknown role of the yttrium ion, the results achieved suggest that the magnetic behavior observed in members of the R-114 family is not necessarily linked to the moment of the rare-earth ion, as in case of YBaCo4O7+δ, since the yttrium ion is not magnetic. Beyond this important finding, the experimental results reported in the present paper demonstrate that the tested chemical route is suitable for synthesizing complex, single-phase oxides, such as the YBaCo4O7+δ cobaltate. The success in synthesizing high-purity YBaCo4O7+δ allows one to subtract parasitic effects from the intrinsic magnetic behavior of this challenging system.

Heisenberg Spin Glass Experiments and the Chiral Ordering Scenario

An overview is given of experimental data on Heisenberg Spin Glass materials so as to make detailed comparisons with numerical results on model Heisenberg spin glasses, with particular reference to the chiral driven ordering transition scenario due to Kawamura and collaborators. On weak anisotropy systems, experiments show critical exponents which are very similar to those estimated numerically for the model Heisenberg chiral ordering transition but which are quite different from those at Ising spin glass transitions. Again on weak anisotropy Heisenberg spin glasses, experimental torque data show well defined in-field transverse ordering transitions up to strong applied fields, in contrast to Ising spin glasses where fields destroy ordering. When samples with stronger anisotropies are studied, critical and in-field behavior tend progressively towards the Ising limit. It can be concluded that the essential physics of laboratory Heisenberg spin glasses mirrors that of model Heisenberg spin glasses, where chiral ordering has been demonstrated numerically.

Effect of Mn Addition on In-Field Behavior of IBAD/MOCVD Gd-YBCO Second Generation HTS Tapes

We analyze the effect of Mn addition to Gd-substituted YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-delta</sub> (YBCO) on transport current and behavior under applied magnetic field. The high-temperature superconducting tapes were manufactured by ion-beam assisted deposition and metal organic chemical vapor deposition on hastelloy substrates. The field dependence measurements as a function of Mn concentration were performed in applied magnetic fields up to 1.5 T at 77 K. The dependence of critical current on the field angle was measured in the plane perpendicular to the sample longitudinal axis (current axis). The effect of Mn concentration on critical temperature is also reported. The results are characterized and discussed.

AC Losses and Magnetic Coupling in Multifilamentary 2G HTS Conductors and Tape Arrays

Striation of coated HTS conductors is a promising way of reducing their ac loss. In particular, loss in the striated conductors is affected by magnetic coupling between the superconducting filaments. We experimentally study the in-field behavior of the planar arrays of superconducting tapes and deduct contribution of such coupling to the net ac loss. This contribution is largest at lowest ac field amplitudes. Dependence of the loss upon the inter-filament separation is studied and results are compared to the existing theoretical models and numerical simulations. We show that magnetization ac loss of practical multi-filamentary conductors can be reasonably fitted with the theoretical result of Mawatari for infinite arrays of magnetically-coupled superconducting strips.

(Tl0.5Pb0.5)(Sr0.8Ba0.2)2Ca2Cu3Oy superconducting thick films with high in-field critical current densities

Superconducting (Tl0.5Pb0.5)(Sr0.8Ba0.2)2Ca2Cu3Oy films with a thickness between 1 and 2 μm are prepared by screen printing the precursor material on monocrystalline lanthanum aluminate substrates followed by ex situ thallination. Texture analysis confirmed that highly c-axis oriented samples with critical temperatures Tc(0) between 117 and 119 K and with transition widths ΔT(90–10%) of 1 K are achieved. The critical current densities in self-field are above 1.2 × 1010 A m−2 at 77 K, and the in-field behaviour is excellent, even without the introduction of artificial pinning centres. jc of 4 × 109 A m−2 at 77 K and 6 T (H || ab) and of 1 × 109 A m−2 at 1 T for H || c are observed.

Transport critical current density of Ag-sheathed Pr-doped (Tl,Cr)Sr2CaCu2O7 superconductor tapes in applied magnetic field

Powder-in-tube Tl-1212 (Tl,Cr)-Sr-(Ca,Pr)-Cu-O/Ag tapes were prepared and processed with different thermomechanical treatments. The processing conditions caused the variation of the transport critical current density (Jc) in the tapes. Tapes subjected to rolling showed lower Jc compared to the pressed tapes. Uniaxial pressing is more effective in densifying the tape cores by forcing the grains into closer contact and enhances the connectivity between grains. All the tapes showed a majority phase of 1212. The existence of 1201 phase considerably reduced Jc in the rolled tapes. Intermediate rolling is not favorable in improving Jc for the irregular grains structure, in contrast to Bi-2223 superconductors with plate-like grains. The in-field behavior of the tapes indicates that they are dominated by weak links as Jc falls rapidly in low applied field (H<0.06 T). No anisotropic transport properties were observed for all the tapes. SEM images showed randomly oriented irregular grains making texturing difficult to achieve. Neither the grain size nor the morphology was changed significantly by the thermomechanical treatments. The observed irregular grains imply that high-angle tilt boundaries were formed with intergranular weak links. Grain morphology is suggested to be the key factor that limits the Jc in these tapes.

Diel Feeding Activity and Thermoregulation by Japanese Beetles (Coleoptera: Scarabaeidae) within Host Plant Canopies

Abstract Patterns of feeding by Japanese beetles, Popillia japonica Newman, were studied in relation to time of day or night and to ambient temperature (Ta). We also measured beetles’ thoracic temperatures (Tth) at rest, during preflight warm up, and during flight, and observed their within-plant distributions in relation to sunlight or shade to gain insight regarding whether their in-field behavior involves physiological and behavioral thermoregulation. Finally, we studied startle response as affected by Ta and time of morning. Japanese beetles fed most extensively within trees from midmorning until late afternoon, but also substantially in evening (1800–2200 hours) and sparingly throughout the night so long as Ta was >15°C. Beetles in the field were capable of endothermy, maintaining elevated Tth independent of basking. At low to moderate Ta (19–32°C), nonflying beetles in shade or direct sunlight had Tth as much as 3.75 or 5.5°C higher, respectively, than Ta. Thoracic temperature was elevated during fl...

Improved in-field behaviour of uranium doped BiSCCO tapes by enhanced flux pinning

Uranium doped BiSCCO 2223 tapes were irradiated by thermal neutrons. The resulting fission-induced defects improve flux pinning and shift the irreversibility line to higher fields. Significant enhancements of the transport critical current density as well as a reduction of the J/sub c/-anisotropy are found for the irradiated samples. Furthermore, inter- and intragranular critical current densities were determined from the remanent magnetic moments by SQUID magnetometry.