Search

The partial discharge inception voltage (PDIV) of low-voltage induction motor turn-turn insulation analogy is investigated for variable relative humidity (RH) of the surrounding air (temperature and pressure are kept constant close to their ambient values). Three materials, perfluoralkoxy alkane, sealed and unsealed alumina (UA), are employed as the dielectric coating (insulation) of test samples. Each material's dielectric properties change differently with RH—of these, relative permittivity is regarded as the most crucial, as it was previously proven to be, along with the coating's thickness, the key factor in determining the PDIV in dry air conditions. To further vary the value of permittivity and thus provide larger data sets for the verification study, the frequency of the excitation voltage is also varied between 1 Hz and 50 kHz. The obtained experimental data are compared against the PDIV predictions obtained by a breakdown model based on the reduced thickness of the coating (ratio of the coating thickness to its relative permittivity). Satisfying agreement between the measured and predicted PDIV are obtained for the first two materials, whereas significant discrepancies are seen for the UA material. For this case, surface conductivity is introduced into the prediction model and much better fits to the experimental data are obtained for a suitable value of surface resistance. It is hence demonstrated that the model is able to satisfactorily predict the PDIV for three substantially different materials when the RH of the surrounding air is varied between 10 % – 80 % . [ABSTRACT FROM AUTHOR]

Workbench-size particle accelerators, enabled by Nb3Sn-based superconducting radio-frequency (SRF) cavities, hold the potential of driving scientific discovery by offering a widely accessible and affordable source of high-energy electrons and x-rays. Thin-film Nb3Sn RF superconductors with high quality factors, high operation temperatures, and high-field potentials are critical for these devices. However, surface roughness, non-stoichiometry, and impurities in Nb3Sn deposited by conventional Sn-vapor diffusion prevent them from reaching their theoretical capabilities. Here we demonstrate a seed-free electrochemical synthesis that pushes the limit of chemical and physical properties in Nb3Sn. Utilization of electrochemical Sn pre-deposits reduces the roughness of converted Nb3Sn by five times compared to typical vapor-diffused Nb3Sn. Quantitative mappings using chemical and atomic probes confirm improved stoichiometry and minimized impurity concentrations in electrochemically synthesized Nb3Sn. We have successfully applied this Nb3Sn to the large-scale 1.3 GHz SRF cavity and demonstrated ultra-low BCS surface resistances at multiple operation temperatures, notably lower than vapor-diffused cavities. Our smooth, homogeneous, high-purity Nb3Sn provides the route toward high efficiency and high fields for SRF applications under helium-free cryogenic operations. [ABSTRACT FROM AUTHOR]

The rapid development of surveillance technology has driven the research of multispectral stealth. Demand for infrared and microwave radar compatible stealth is becoming increasingly urgent in military applications. Herein, a versatile metamaterial absorber is designed and fabricated to simultaneously achieve ultra-broadband radar scattering reduction, low infrared emission, and high optical transparency. The designed structure consists of an infrared stealth layer, radar absorption layers, and backing ground. The infrared stealth layer employs specifically indium tin oxide (ITO) square patches, while the radar absorption layers can be obtained by stacking different size ITO patterned films of the same structure with high surface resistances, realizing broadband microwave stealth performance in the 1.98–18.6 GHz frequency range with an incident angle of 45°. The broad radar stealth and low infrared emissivity of 0.283 are consistent with the simulations and calculations. Furthermore, the designed structure exhibits characteristics such as polarization insensitivity, wide incident angles, optical transparency, and flexibility, allowing for a wide range of applications in various environments. [ABSTRACT FROM AUTHOR]

Three 1.3 GHz nine-cell large-grain superconducting niobium cavities were investigated with medium-temperature baking, using buffered chemical polishing to remove the impurity profiles from previous heat treatments. The average intrinsic quality factor in 2 K vertical tests of the cavities was 2.7 × 1010 at 16 MV m−1 with maximum accelerating gradients of 20–22 MV m−1. These promising values confirmed the effectiveness of an improved medium-temperature baking recipe for niobium cavities, beneficial for superconducting radiofrequency applications. Furthermore, resistance analysis demonstrated that medium-temperature baking reduced both the Bardeen–Cooper–Schrieffer (BCS) resistance and the residual resistance of the cavities. Impurity analysis on niobium samples provided some proof that the reduction in BCS resistance was due to the shortened electron mean free path while the reduction in residual resistance was probably associated with mitigation of the increase in interstitial impurity atoms. [ABSTRACT FROM AUTHOR]

Glypican-3 (GPC3) is a serum marker for hepatocellular carcinoma (HCC) and has excellent specificity and sensitivity. Herein, the construction of an electrochemical aptasensor based on reduced graphene oxide-carboxymethyl chitosan-hemin-palladium nanoparticles (RGO-CMCS-Hemin/Pd NPs) and GPC3 aptamer (GPC3apt) has the function of GPC3 identification and analysis. RGO-CMCS-Hemin/Pd NPs has excellent biocompatibility, large specific surface area and good electrical conductivity, which is not only used as advanced sensing materials to modify the electrode surface to reduce the resistance and increase the signal amplitude, but also used as an electroactive substance to provide electrical signals. GPC3apt as a biometric element makes the aptasensor has good specificity and sensitivity. The GPC3apt can combine with GPC3 and form GPC3-aptamer conjugation, which increases the electron transfer impedance and changes the electrical signal. Under the optimum conditions, the aptasensor had a good linear relationship with the GPC3 concentration in the range of 1.0–100.0 ng ml−1 with R2 of 0.9573. The lower limit of detection was 1.0 ng ml−1 . When the aptasensor was applied to GPC3 detection in human serum samples, the recovery was 93.73%–118.83%. In addition, the GPC3 aptasensor has excellent specificity, reproducibility and stability, which is anticipated to be applied for the clinical detection of GPC3. [ABSTRACT FROM AUTHOR]

In this work, the electrocatalytic properties of novel cathodes prepared by infiltration of NdBa0.9Co2O5+δ (NBC) into porous Gd doped Ceria (GDC) scaffolds are investigated, and comparison is provided with La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) infiltrated GDC cathodes. For both formulations, symmetric cells are fabricated by blade coating and infiltration of aqueous nitrate precursor solutions until reaching 25% w/w load. The effects of the calcination temperature are explored between 750 °C and 950 °C for the NBC-GDC cathodes. Electrochemical impedance spectroscopy and polarization experiments are performed to study the electrocatalytic activity in the oxygen reduction reaction. Compared to LSCF-GDC, a remarkable improvement of the polarization resistance is found on the best performing NBC-GDC cathode between 500 °C and 700 °C (0.022 Ω cm² vs 0.1 Ω cm² at 700 °C). A shift in the rate determining step characterizes the performance of the NBC-GDC cathode above 650 °C, wherein the interfacial oxide ion transfer resistance prevails, while below 650 °C the surface exchange resistance dominates. Different stability behaviors are observed in ageing experiments up to 200 h: the NBC-GDC electrodes show constant ohmic resistance and moderate improvement of the polarization resistance at 700 °C and 550 °C, while the LSCF-GDC electrodes experience degradation. [ABSTRACT FROM AUTHOR]

The variation behaviors of the morphology, transmission, and sheet resistance of the surface Ag/AgO nano-network (NNW) structures fabricated under different illumination conditions and with different Ag deposition thicknesses and thermal annealing temperatures in forming initial Ag nanoparticles (NPs) are studied. Generally, an NNW structure with a smaller mesh size or a denser branch distribution has a lower transmission and a lower sheet resistance level. Under the fabrication condition of a broader illumination spectrum, a lower thermal annealing temperature, or a thicker Ag deposition, we can obtain an NNW structure of a smaller mesh size. The mesh size of an NNW structure is basically controlled by the seed density of Brownian tree (BT) at the beginning of light illumination. A BT seed can be formed through a stronger local localized surface plasmon resonance for accelerating Ag oxidation in a certain region. Once an Ag/AgO BT seed is formed, the surrounding Ag NPs are reorganized to form the branches of a BT. Multiple BTs are connected to form a large-area NNW structure, which can serve as a transparent conductor. Under the fabrication conditions of a broader illumination spectrum, 3 nm Ag deposition, and 100 °C thermal annealing, we can implement an NNW structure to achieve ∼1.15 ÎĽ m in mesh size, ∼90 Ω sqâˆ'1 in sheet resistance, and 93%â€"77% in transmittance within the wavelength range between 370 and 700 nm. [ABSTRACT FROM AUTHOR]

The process of evapotranspiration transfers liquid water from vegetation and soil surfaces to the atmosphere, the so-called latent heat flux ( ${Q_{{\text{LE}}}}$ ), and modulates the Earth’s energy, water, and carbon cycle. Vegetation controls ${Q_{{\text{LE}}}}$ by regulating leaf stomata opening (surface resistance ${r_{\text{s}}}$ in the Big Leaf approach) and by altering surface roughness (aerodynamic resistance ${r_{\text{a}}}$ ). Estimating ${r_{\text{s}}}$ and ${r_{\text{a}}}$ across different vegetation types is a key challenge in predicting ${Q_{{\text{LE}}}}$ . We propose a hybrid approach that combines mechanistic modeling and machine learning for modeling ${Q_{{\text{LE}}}}$ . The hybrid model combines a feed-forward neural network which estimates the resistances from observations as intermediate variables and a mechanistic model in an end-to-end setting. In the hybrid modeling setup, we make use of the Penman–Monteith equation in conjunction with multi-year flux measurements across different forest and grassland sites from the FLUXNET database. This hybrid model setup is successful in predicting ${Q_{{\text{LE}}}}$ , however, this approach leads to equifinal solutions in terms of estimated physical parameters. We follow two different strategies to constrain the hybrid model and therefore control for the equifinality that arises when the two resistances are estimated simultaneously. One strategy is to impose an a priori constraint on ${r_{\text{a}}}$ based on mechanistic assumptions (theory-driven strategy), while the other strategy makes use of more observational data and adds a constraint in predicting ${r_{\text{a}}}$ through multi-task learning of both latent and sensible heat flux ( ${Q_{\text{H}}}$ ; data-driven strategy) together. Our results show that all hybrid models predict the target variables with a high degree of success, with ${R^2}$ = 0.82–0.89 for grasslands and ${R^2}$ = 0.70–0.80 for forest sites at the mean diurnal scale. The predicted ${r_{\text{s}}}$ and ${r_{\text{a}}}$ show strong physical consistency across the two regularized hybrid models, but are physically implausible in the under-constrained hybrid model. The hybrid models are robust in reproducing consistent results for energy fluxes and resistances across different scales (diurnal, seasonal, and interannual), reflecting their ability to learn the physical dependence of the target variables on the meteorological inputs. As a next step, we propose to test these heavily observation-informed parameterizations derived through hybrid modeling as a substitute for ad hoc formulations in Earth system models.

The solution-processed thin-film transistors (TFTs) have become the core requirement for the flexible and transparent electronics industry since they are fabricated using cost-effective techniques. However, the fabrication of low-dimensional TFTs by the solution-processing technique is still a challenge due to the surface contact resistance (ρc). The current study introduces a controllable ρc involving the effect of dimensions (channel width/length = W/L) on TFTs. The ρc was measured to be 2.04 × 109µm VA−1 when the channel length (L) of the TFT was 40 µm. A substantial drop in the surface contact resistance to 1.8 × 108µm VA−1 was found with L = 5 µm. Thus, a 91% control on ρc was obtained when L reduced to 40 µm from 5 µm. Such a controllable ρc was observed with respect to different dimensions of the TFTs. Indeed, an extreme control was obtained in the drain saturation current from 8 µA to 0.8 µA with respect to variation in dimension (W/L) from 15 to 2.5. [ABSTRACT FROM AUTHOR]

Reference electrodes are used in testing and designing thin-film cells in order to distinguish the effects of the positive and negative electrodes and determine the sources of significant resistance (or impedance), but the reference electrode introduces some distortion into the measurement due to non-uniformity of the current distribution. This often arises due to edge effects, the size and placement of the reference electrode, or both. Two common geometries for placing reference electrodes are internally, between the cathode and anode, and externally at a distance from the cathode and anode. Each design introduces some level of distortion, which must be clarified. This work focusses on internally-placed wire reference electrodes and elucidates the artifacts in cell impedance measurements as a function of wire size and wire surface resistance. Published simulations of impedance artifacts rely on computationally-intensive computer simulations, but we develop a simple formula to accurately approximate these effects. The formula is derived using a singular perturbation approximation to the impedance and then combining it with a simple equivalent circuit. Some comparisons with detailed numerical simulations show the accuracy of the resulting formula as a function of the diameter of the reference wire and its surface resistance. [ABSTRACT FROM AUTHOR]

Nb3Sn (TC ≈ 18 K and HSh ≈ 400 mT) is a prospective material to replace Nb (TC ≈ 9 K and Hsh ≈ 200 mT) in SRF accelerator cavities for significant cost reduction and performance enhancement. Because of its material properties, Nb3Sn is best employed as a thin film (coating) inside an already built RF cavity structure. A particular test cavity noted as C3C4 was a 1.5 GHz single-cell Nb cavity, coated with Nb3Sn using Sn vapor diffusion process at Jefferson Lab. Cold measurements of the coated cavity indicated the superconducting transition temperature of about 18 K. Subsequent RF measurements indicated field-dependent surface resistance both at 4.3 and 2.0 K. After initial cold measurements, the cavity RF loss distribution was studied with a thermometry mapping system. Loss regions were identified with thermometry and were cut out for material analysis. The presence of significantly thin patchy regions and other carbon-rich defects is associated with strong local field-dependent surface resistance. This paper summarizes RF and thermometry results correlated with material science findings. [ABSTRACT FROM AUTHOR]

We have investigated the response of the high entropy alloy of CoNiCrFeMn to the bombardment under extreme irradiation flux by means of molecular dynamics simulations. Compared to pristine Ni single crystalline, the CoNiCrFeMn HEA had less point defects during a single primary knock-on atom process. The average depth of defects was shallower. For consecutive bombardments, the CoNiCrFeMn HEA demonstrated much higher surface irradiation resistance than pristine Ni. Under the irradiation flux of 5.59 × 1027 n/(m^2*s), the number of defects in Ni gradually increased and was proportional to the number of bombardments, till the formation of dislocation which led to a boost of the defects. On the contrary, the number of defects in CoNiCrFeMn HEA was much less and stable, appearing to be insensitive to the number of bombardments and suggesting good radiation resistance. Such radiation resistance of CoNiCrFeMn HEA was attributed to the lattice distortion and sluggish diffusion of atoms, which could enhance the recombination of defects. Under the irradiation flux of 1.68 × 1028 n/(m^2*s), the boost of the defects in Ni occurred at lower number of bombardments. In addition, under both the irradiation flux of 5.59 × 1027 and 1.68 × 1028 n/(m^2*s), CoNiCrFeMn HEA had a smaller number of point defects and the defects were well dispersed. Our results showed that compared with Ni matrix, CoNiCrFeMn HEA had higher surface bombardment tolerance. This study might be helpful in the design of first-wall materials under the extreme irradiation flux. [ABSTRACT FROM AUTHOR]

The surface resistance of state-of-the-art REBa2Cu3O7−x coated conductors has been measured at 8 GHz versus temperature and magnetic field. We show that the surface resistance of REBa2Cu3O7−x strongly depends on the microstructure of the material. We have compared our results to those determined by the rigid fluxon model. The model gives a very good qualitative description of our data, opening the door to unravel the effect of material microstructure and vortex interactions on the surface resistance of high temperature superconductors. Moreover, it provides a powerful tool to design the best coated conductor architecture that minimizes the in-field surface resistance. We have found that the surface resistance of REBa2Cu3O7−x at 50 K and up to 9 T is lower than that of copper. This fact poses coated conductors as strong candidate to substitute copper as a beamscreen coating in CERN’s future circular collider. To this end we have also analyzed the secondary electron yield (SEY) of REBa2Cu3O7−x and found a compatible coating made of sputtered Ti and amorphous carbon that decreases the SEY close to unity, a mandatory requirement for the beamscreen chamber of a circular collider in order to prevent the electron-cloud phenomenon. [ABSTRACT FROM AUTHOR]

Different passivation techniques are investigated for reducing leakage current in small pixel (down to 9 μm) heterostructure photodetectors designed for the short-wavelength infrared range. Process evaluation test chips were fabricated using the same process as for focal plane arrays. Arrays of small photodetectors were electrically characterized under dark conditions from 150 K to room temperature. In order to evaluate the leakage current, we studied the relation between the inverse of dynamic resistance at −20 mV and zero bias and perimeter over area P/A ratio as the pixel size is scaled down. At 150 K, leakage current arising from the perimeter dominates while bulk leakage dominates at room temperature. We find that in shortwave devices directly underfilling hybridized devices with a thermoset epoxy resin without first doing any additional passivation/protection after etching gives the lowest leakage with a surface resistance of 4.2 × 109 and 8.9 × 103 Ω cm−1 at 150 and 300 K, for −20 mV of bias voltage, respectively. [ABSTRACT FROM AUTHOR]

We demonstrate that arrays of flat gold nanodisks with rectangular lattices can support a tunable hybrid frequency gap formed by the surface lattice resonances in the substrate ((+1, 0)sub) and the superstrate ((−1, 0)sup). For a certain polarization, rotation of the arrays reduces this gap, forming a band crossing (degenerate state) wherein both surface lattice resonances happen around a single wavelength (∼1300 nm). This highlights a situation wherein hybridization of the Rayleigh anomaly with localized surface plasmon resonances with different multipolar natures happens around the same wavelength. We demonstrate that for a different polarization of the incident light the arrays support the formation of a photonic–plasmonic state at about 1650 nm. Our results show that as the projection of the wave vector of the incident light on the planes of the nanodisk arrays increases, within a given wavelength range, the (+1, 0) mode of this state becomes amplified. Under this condition, this mode can undergo a significant blue shift without broadening, while its amplitude increases. [ABSTRACT FROM AUTHOR]

An overview of a theory of electromagnetic response of superconductors in strong radio-frequency (RF) electromagnetic fields is given with the emphasis on applications to superconducting resonant cavities for particle accelerators. The paper addresses fundamentals of the BCS surface resistance, the effect of subgap states and trapped vortices on the residual surface resistance at low RF fields, and a nonlinear surface resistance at strong fields, particularly the effect of the RF field suppression of the surface resistance. These issues are essential for the understanding of the field dependence of high quality factors achieved on the Nb cavities at 1.3–2 K in strong RF fields Ba close to the depairing limit, and the extended rise which has been observed on Ti and N-treated Nb cavities. Possible ways of further increase of and the breakdown field by optimizing impurity concentration at the surface and by multilayer nanostructuring with materials other than Nb are discussed. [ABSTRACT FROM AUTHOR]

In the present study the radio-frequency complex response of trapped vortices in superconductors is calculated and compared to experimental data previously published. The motion equation for a magnetic flux line is solved assuming a bi-dimensional and mean-free-path-dependent Lorentzian-shaped pinning potential. The resulting surface resistance shows the unprecedented bell-shaped trend as a function of the mean-free-path observed in our previous experimental work. We demonstrate that such bell-shaped trend of the surface resistance as a function of the mean-free-path may be described as the interplay of the two limiting regimes of the surface resistance, for low and large mean-free-path values: pinning and flux-flow regimes respectively. Since the possibility of defining the pinning potential at different locations from the surface and with different strengths, we discuss how the surface resistance is affected by different configurations of pinning sites. By tackling the frequency dependence of the surface resistance, we also demonstrate that the separation between pinning- and flux-flow-dominated regimes cannot be determined only by the depinning frequency. The dissipation regime can be tuned either by acting on the frequency or on the mean-free-path value. [ABSTRACT FROM AUTHOR]

The surface resistance Rs of superconducting materials can be obtained by measuring the quality factor of an elliptical cavity excited in a transverse magnetic mode (TM010). The value obtained has however to be taken as averaged over the whole surface. A more convenient way to obtain Rs, especially of materials which are not yet technologically ready for cavity production, is to measure small samples instead. These can be easily manufactured at low cost, duplicated and placed in film deposition and surface analytical tools. A commonly used design for a device to measure Rs consists of a cylindrical cavity excited in a transverse electric (TE110) mode with the sample under test serving as one replaceable endplate. Such a cavity has two drawbacks. For reasonably small samples the resonant frequency will be larger than frequencies of interest concerning SRF application and it requires a reference sample of known Rs. In this article we review several devices which have been designed to overcome these limitations, reaching sub-nΩ resolution in some cases. Some of these devices also comprise a parameter space in frequency and temperature which is inaccessible to standard cavity tests, making them ideal tools to test theoretical surface resistance models. [ABSTRACT FROM AUTHOR]

We study depth profiling of the microwave surface resistance (RS) of GdBa2Cu3O7−δ (GdBCO) coated conductors (CCs) grown using the reactive co-evaporation by deposition and reaction (RCE-DR) method, a method enabling extremely high deposition rate. GdBCO CCs with the critical current (IC) of more than 790 A cm−1 at 77 K in self-field are used for the study. The RS of the GdBCO CCs is measured at temperatures of 10–80 K using a 8.5 GHz TE011-mode rutile resonator, which is compared with that of YBa2Cu3O7−δ films and GdBCO films epitaxially grown on single crystal substrates. It turns out that there is significant inhomogeneity in the RS over the thickness of the GdBCO layer, with the RS value of the top part at 30 K being almost two times higher than the corresponding one of the bottom part. A transmission electron microscopy study reveals that Gd2O3 grains coexist with GdBCO grains with the average Gd2O3 grain sizes being ∼150 nm at the top and ∼100 nm at the bottom of the GdBCO layer. We relate the inhomogeneity in the RS of the GdBCO layer with the positional dependence of the Gd2O3 grain size, for which effects of the dielectric losses from the Gd2O3 grains on the measured RS of the GdBCO layer are considered. Our results imply that the critical current density, another important transport property of superconductors, could be inhomogeneous over the thickness of the GdBCO layer grown using the RCE-DR method. [ABSTRACT FROM AUTHOR]

Cu ion implantation and subsequent rapid annealing at 500°C in N2 result in low surface resistivity of 1.611 ohm/sq with high mobility of 290 cm2 V−1 S−1 for microcrystalline diamond (MCD) films. Its electrical field emission behavior can be turned on at E0 = 2.6 V/μm, attaining a current density of 19.5μA/cm2 at an applied field of 3.5 V/μm. Field emission scanning electron microscopy combined with Raman and x-ray photoelectron microscopy reveal that the formation of Cu nanoparticles in MCD films can catalytically convert the less conducting disorder/a-C phases into graphitic phases and can provoke the formation of nanographite in the films, forming conduction channels for electron transportation. [ABSTRACT FROM AUTHOR]