Effective Surface Resistance Research Articles

Biocathode electrochemical activity and reduction characteristics of Cr(VI) system in microbial fuel cells

AbstractBACKGROUNDThe biocathode of microbial fuel cells (MFCs) offers a simple method for the reductive treatment of Cr(VI), and Cr(VI) is an electron acceptor in cathodes in MFCs. In this study, MFCs with different Cr(VI) contents (7.07–35.35 mg L−1) were considered to evaluate the overall performance of MFCs.RESULTSThe results of electrochemical analysis confirmed that the MFC‐2 biocathode exhibited a higher effective reaction surface, stronger conductivity, and smaller charge transfer resistance (53.63 Ω) than the others. In addition, Cr(VI) had a power output of 75.6 mW m−2 in MFC‐2 and a Cr(VI) cathodic coulombic efficiency of 103.8%. With 14.14 mg L−1 Cr(VI) content, the cathode microbe had the best activity. Cr(VI) reduction followed a pseudo‐first‐order kinetic model, with the rate constant being 0.0139 h−1. Meanwhile, this study analyzed the Cr(VI) reduction in MFCs and the release and acceptance of electrons and protons. Electrically active bacteria such as Proteobacteria were highly enriched on the anode and cathode biofilm, while the Cr(VI)‐reducing bacteria Gammaproteobacteria increased in the biofilm of the cathode.CONCLUSIONThis study helps in the selection of Cr(VI) concentration for the cathode, guaranteeing microbial activity and power generation performance. Microbes have the best electrochemical activity in MFC‐2 (14.14 mg L−1). Meanwhile, the change in anode microbial activity was affected by cathode performance. The microbial community was significantly influenced by Cr(VI). © 2023 Society of Chemical Industry (SCI).

Radio Absorbing Structure Based on Arrays of Resistive Squares

A periodic structure consisting of plane arrays of resistive squares located in a dielectric layer on a metal mirror is considered. On the basis of the solution of the problem of diffraction of a normally incident electromagnetic wave by this structure, the optimal structure parameters that provide for the minimal reflection coefficient in a given wavelength range are calculated. It is shown that, when the number of arrays is up to three, the approximate calculation of the reflection coefficient of a fine-meshed structure can be performed using the method, in which the arrays are matched with films that have the effective surface resistance calculated on the basis of the solution of the quasi-static problem. It is also shown that the optimized investigated structure has the reflection level that is lower than the reflection level of the optimized known structure based on resistive films.

Homogeneity in the Microwave Surface Resistance of Large YBa2Cu3O7−δ Superconductor Films Coated with Au

We studied homogeneity in the microwave surface resistance of Au-coated YBa2Cu3O7−δ (Au/YBCO) films. The Au/YBCO film with 4-inches in diameter was prepared in-situ with the thicknesses of 68 nm and 365 nm for the Au layer and the YBa2Cu3O7−δ (YBCO) layer, respectively. We measured the effective surface resistance (RS,eff) of the Au/YBCO film at temperatures of 25 K, 60 K, 70 K, and 77 K, respectively, at 29 different positions on the film. The RS,eff values were analyzed with the finite thicknesses of the Au and the YBCO layers taken into consideration. The local RS,eff values of the Au/YBCO film appeared to be almost uniform at 25 K. Meanwhile significant positional dependences were observed for the RS,eff of the Au/YBCO film at 60 K, 70 K and 77 K, respectively, which seemed to be due to non-uniform local penetration depth (λ) of the YBCO layer rather than due to variations in the local real-part conductivity of the YBCO layer. The observed results could not be attributed to the properties of the Au layer. At temperatures below the critical temperature of YBCO, the observed RS,eff values of the Au/YBCO film were significantly lower than those estimated using the surface resistance of Au and YBCO, which reflected proximity effects of the normal-metal Au layer in contact with the superconducting YBCO layer. Homogeneity in the RS,eff of the Au/YBCO film might be correlated with the distributions in the local λ of the YBCO layer, providing valuable information needed for designing microwave filters.

Enhancement of effective linear RF surface resistance of superconducting surfaces by microscopic topography

Minimization of Radio-Frequency (RF) dissipation on superconducting surfaces is of interest for many applications. A prominent one is the use of Superconducting RF (SRF) cavities for charged particle acceleration. In addition to our previous investigation which characterized the occurrence of high-field non-linear losses by microscopic surface topography, the topic of increased linear losses as a function of surface topographic character merits consideration. Surfaces with isotropic homogeneous surface topography may be well characterized by power spectral density (PSD) derived from systematic height measurements. PSD characterizations of representative niobium cavity surface treatments have been developed: Electro-Polishing (EP), Nano-Mechanical Polishing (NMP) and Centrifugal Barrel Polishing (CBP) A perturbation model based on PSD statistical analysis is used to calculate additional RF loss on these surfaces when superconducting. The model assesses the penetration depth effects for a superconductor. We thus estimate the RF power dissipation ratio between these rough surfaces and an ideal smooth surface.

Compact facility for testing steady and transient thermal performance of building walls

Energy efficiency retrofit of buildings represents a key effort in reducing EU energy demand by 20% by 2020. However, predictions tend to overestimate savings by large percentages. The shortfall in savings can be attributed to incorrect predictive techniques, comfort takeback along with other behavioural and workmanship variables. Common predictive techniques related to heat loss tend to be based on the U-value of the building envelope. This paper presents the design of a more straightforward and compact version of the traditional Hot-Box apparatus (measures U-value) which instead determines the thermal resistance of samples of building envelope. U-value includes the need to measure/predict the effective surface resistances. In situ surface resistances, which include radiation and convection, are difficult to predict and vary depending on climatic conditions, exposure levels, surface emissivities among many other influences. The design of the test facility eliminates the need to incorporate these surface behaviour variables. This paper details the replicable apparatus and test methodology. The results of testing a hollow block wall of typical construction using the rig is then presented. The determined R-value is found to be within 1% of calculated values and the thermal time constant also matches closely with the most accurate predictive estimates.

Noninvasive thickness measurements of metal films through microwave dielectric resonators

Thicknesses of Pt films ranging from 60 to 950 nm are measured noninvasively using a TE011-mode dielectric resonator with the resonant frequency of 8.5 - 9.8 GHz at temperatures of 77 K and 293 K. A cylindrical rutile rod is used as the dielectric, with a high-TC superconductive YBa2Cu3O7−δ film used as the bottom endplate of the resonator for measurements at 77 K. This method is based on two facts: i) Due to the electromagnetic interferences of incoming and reflected waves at the surface of the metal film surface, the effective surface resistance varies with the film thickness, and ii) the intrinsic surface resistance of normal metals is equal to the intrinsic surface reactance in the local limit. The measured thicknesses using the rutile resonator appear to be comparable with those obtained using a profilometer.

Modification of evapotranspiration model based on effective resistance to estimate evapotranspiration of maize for seed production in an arid region of northwest China

Summary To estimate evapotranspiration (ET) of heterogeneous canopy of maize for seed production accurately, an ET model was developed based on effective resistance after field experiments were conducted from March to September in 2013 and 2014 in an arid region of northwest China. The effective resistance of maize including effective surface (rce) and aerodynamic (rae) resistance was estimated using different methods, and then the Penman–Monteith model (P–M model) based on effective resistance was used to estimate daily ET of maize over the whole growing stage. Results showed that when the fraction cover of the canopy (fc) = 1, the estimated rce by aggregating female and male canopy resistances in parallel, was closer to the measured rce (rcec), which was obtained by inverting the P–M model based on effective resistance using measured ET by the eddy covariance (EC) system. When fc

Unusual microwave response and bulk conductivity of very thin FeSe0.3Te0.7 films as a function of temperature

Results of X-band microwave surface impedance measurements of FeSe1−xTex very thin film are reported. The effective surface resistance shows appearance of peak at T ≤ Tc when plotted as a function of temperature. The authors suggests that the most well-reasoned explanation can be based on the idea of the changing orientation of the microwave magnetic field at a S–N phase transition near the surface of a very thin film. The magnetic penetration depth exhibits a power-law behavior of δλL(T) ∝ CTn, with an exponent n ≈ 2.4 at low temperatures, which is noticeably higher than in the published results on FeSe1−xTex single crystal. However the temperature dependence of the superfluid conductivity remains very different from the behavior described by the BCS theory. Experimental results are fitted very well by a two-gap model with Δ1/kTc = 0.43 and Δ2/kTc = 1.22, thus supporting s±-wave symmetry. The rapid increase of the quasiparticle scattering time is obtained from the microwave impedance measurements.

Concentration of trisodium citrate by electrodialysis

In this work, the experimental procedure and mathematical model formerly developed was used to describe the electrodialytic (ED) recovery of trisodium citrate. By performing several voltage–current, electro-osmosis and desalination tests, the main engineering parameters (i.e., the ion transport numbers in solution and membranes, effective solute and water transport numbers, effective surface area and resistances of membranes, and limiting electric current) of the ED process under study were assessed.As expected, the electric resistance of the cationic membranes (Rc) resulted to be about constant (0.11±0.02Ω) and independent of solute concentration, while that of the anionic ones (Ra) was not only greater than Rc, but also dependent on both the current applied and solute concentration. Moreover, in the ohmic region of the current–voltage curves Ra appeared to be a logarithmic function of the solution electric conductivity in the dilute compartment. On condition that the current applied was less than 2/3 of the limiting current for the cationic membrane (Ilim,c) the time course of the voltage applied to the ED stack when operating at a constant current of 0.75 or 1.5A was adequately predicted with a mean percentage error of ~20%.

Superconducting surface impedance under radiofrequency field

Based on BCS theory with moving Cooper pairs, the electron states distribution at 0K and the probability of electron occupation with finite temperature have been derived and applied to anomalous skin effect theory to obtain the surface impedance of a superconductor under radiofrequency (RF) field. We present the numerical results for Nb and compare these with representative RF field-dependent effective surface resistance measurements from a 1.5GHz resonant structure.

Surface Impedance of YBa2Cu3O7−δ Films Grown on MgO Substrate as a Function of Film Thickness

The surface impedance characteristics of epitaxial YBa2Cu3O7−δ films of thickness df = 75, 150, 300, 600 nm, produced by magnetron thermal co-evaporation onto single crystal MgO substrates was studied using measurement technique based on Ka-band whispering gallery mode (WGM) dielectric resonator (DR) fabricated from single crystal sapphire. Characterization of the unpatterned films was carried out in temperature interval from 20 K to 90 K. It was shown that the effective surface resistance approaches the minimum value for df>300 nm. At the same time, intrinsic impedance properties are practically independent on df in the studied interval of df values. The temperature dependence of London penetration depth was estimated experimentally and approximated with the model expressions. Effect of reducing the surface resistance of approximately two times at low temperatures one year later after their manufacture was registered for all films(except the film of 75 nm thickness). The effect may be explained by changes of the film parameters in time after the film light overdoping.

Improved measurement accuracy for the thickness of YBa2Cu3O7−δ films by using a single two-resonance-mode sapphire resonator

We measure the thickness of YBa2Cu3O7−δ (YBCO) films at a microwave frequency of 39.91 GHz noninvasively by using the single two-resonance-mode sapphire resonator (TSR) method. In the TSR method, a single sapphire resonator is used for measuring the effective surface resistance (RS,eff) and the penetration depth (λ) of the YBCO films at the same frequency at temperatures of 6–88 K. Five YBCO films having thicknesses of 70–360 nm are used in this study. The thickness, t(RF), of the YBCO films as measured at 10, 30, 50, and 77 K by using the TSR method turns out to be almost the same as the corresponding one, t(step), as measured by using step profilometry. The differences between t(RF) and t(step) appear to be less than ∼5% regardless of the film thickness and the measured temperature, which is smaller than the corresponding value of ∼7% as observed by using the two-resonance-mode rutile resonator (TRR) method. The differences between the average t(RF) of each YBCO film and the corresponding t(step) turn out to be less than ∼3% in both methods. We discuss the merits in using the TSR method in relation with the TRR method. Our study shows that the TSR method could be very useful for noninvasive measurements of the thicknesses of various superconductor films with accuracy by using microwaves.

Temperature dependence of transmittance and effective surface resistance of MgB 2 film

Using the Kubo formula approach and Green's function method, the temperature dependence of the transmittance and effective surface resistance of high quality MgB 2 film are calculated in the framework of the two-band model. For large interval of temperatures below T C our results are in agreement with experimental data. We show a single-gap model based on BCS theory, which is insufficient to understand such quantities, but a two-band model with different symmetries can describes the experimental data rather well. In the two-gap model we consider that the transmittance and effective surface resistance are a weighted sum of the contributions from σ and π bonds and hybridization between them is negligible.

MICROWAVE PROPERTIES OF A HIGH-TEMPERATURE SUPERCONDUCTOR AND FERROMAGNETIC BILAYER STRUCTURE

Microwave properties for a bilayer structure made of the high-temperature superconducting and the ferromagnetic materials are theoretically investigated. The properties are explored through the effective surface impedance calculated by using the enhanced twofluid model for high-temperature superconductors together with the transmission line theory. The calculated effective surface impedance will be numerically analyzed as a function of the frequency, the temperature, and the thicknesses of the constituent layers. It is found that, for a thinner superconducting film, the effective surface resistance is a strong function of the frequency, and the effective surface reactance exhibits a peak and a dip in the frequency-domain. In the study of the effect of thickness in ferromagnetic substrate, there is a peak frequency in the surface reactance for a thinner substrate. There is also a threshold thickness for the ferromagnetic substrate such that it behaves like a bulk substrate when its thickness is larger than this threshold value. In the temperature dependence of surface reactance, the peak near critical temperature is shifted to lower temperature and broadened as the film thickness decreases. Received 13 November 2010, Accepted 15 December 2010, Scheduled 19 December 2010 Corresponding author: Chien-Jang Wu (jasperwu@ntnu.edu.tw).

Non-Invasive Measurements of Thickness of Superconductor Films by Using Two-Resonant-Mode Rutile Resonator

The film thickness should be known for extracting the intrinsic surface resistance from the effective surface resistance as measured by using the dielectric resonator method. Thicknesses of 70 nm to 360 nm are measured for YBa2Cu3O7−δ films in a non-invasive way by using the two-resonant-mode dielectric resonator (TDR) method. A rutile resonator with the respective resonant frequencies of 15.25–15.61 GHz and 15.10–15.37 GHz for the TE021 and the TE012 modes is used for this purpose. Differences between the values as measured by using the TDR technique and those measured by using a step profilometer appear to be less than 3%, which is smaller than the previous value of 5% as measured by using a 8.6 GHz single-resonance mode rutile resonator [Lee et al. J. Korean Phys. Soc. 54(2009)1619]. Merits of using the TDR method are discussed.

Relationship between intrinsic surface resistance and critical current density of YBCO thin films with various thickness

We investigated the relationship between the intrinsic surface resistance (Rsint) and critical current density (Jc) of YBa2Cu3Oy (YBCO) film thinner than the penetration depth (λL). The measured YBCO films were deposited on CeO2-buffered r-cut Al2O3 substrates by the pulsed laser deposition method. The thicknesses of these films were 300, 200, and 100nm, respectively. The Rsint means the surface resistance of YBCO film removing the loss by the impedance of the substrates. The effective surface resistance (Rseff) including the impedance of the substrate and the Jc of each YBCO film were measured using the dielectric resonator method at 21.8GHz and the inductive method. We calculated Rsint by using phenomenological expressions and the Rseff value. The Rsint values of each YBCO film were almost the same in the measured temperature region. As a result, we found that Rsint was in inverse proportion to the Jc of YBCO film thinner than λL.

Effective Surface Impedance of a High-Temperature Superconducting Film in Semiconductor Plasma Substrate at Mid-infrared Frequency

The effective surface impedance of a high-temperature superconducting thin film on a semiconductor plasma substrate is calculated. Two possible configurations are considered. The first one is a superconducting film deposited on a semi-infinite semiconductor substrate. It is seen that there exists a critical film thickness for the superconductor such that a minimum effective surface resistance is attained. The effective surface resistance is strongly dependent on the high-frequency permittivity of semiconductor plasma. The second will be limited to the more practical case, that is, the semiconductor substrate is of finite thickness. The investigation of substrate resonance in the effective surface resistance shows some fundamental distinctions when a semiconductor plasma substrate is introduced.

On the link between potential evaporation and regional evaporation from a CBL perspective

The relationship between potential evaporation and actual evaporation was first examined by Bouchet (Proc Berkeley Calif Symp IAHS Publ, 62:134–142, 1963) who considered potential evaporation as the consequence of regional evaporation due to atmospheric feedbacks. Using a heuristic approach, he derived a complementary relationship which, despite no real theoretical background, has proven to be very useful in interpreting many experimental data under various climatic conditions. Here, the relationship between actual and potential evaporation is reinterpreted in the context of the development of the convective boundary layer (CBL): first, with a closed-box approach, where the CBL has an impermeable lid; and then with an open system, where air is exchanged between the CBL and its external environment. By applying steady forcing to these systems, it is shown that an equilibrium state is reached, where potential evaporation has a specific equilibrium formulation as a function of two parameters: one representing large-scale advection and the other the feedback effect of regional evaporation on potential evaporation, i.e. a kind of “medium-scale advection”. It is also shown that the original form of Bouchet’s complementary relationship is not verified in the equilibrium state. This analysis leads us to propose a new and more rational approach of the relationship between potential and actual evaporation through the effective surface resistance of the region.

Effective Surface Impedance for a Superconductor-Semiconductor Superlattice at Mid-Infrared Frequency

The effective surface impedance for a superconductor-semiconductor superlattice at mid-infrared frequency is calculated based on the transfer matrix method together with the enhanced two-fluid model for the high-temperature superconductor. We first investigate the effective surface resistance and surface reactance in the case of normal incidence. We find that there is a critical thickness for superconductor film such that a minimum loss is attained. We next study the effective surface impedance under the oblique incidence. The calculated effective surface impedance indicates that the angle-dependent feature is only seen for the single period. However, it does not rely on the number of periods when the period is greater than two and, in the meantime, the surface resistance is nearly unchanged as a function of the angle of incidence.

Strong reduction of the field-dependent microwave surface resistance in YBCO with BaZrO3 inclusions

We present measurements of the magnetic field dependent microwave surface resistance in laser-ablated YBa2Cu3O7-δ films on SrTiO3 substrates. BaZrO3 crystallites were included in the films using composite targets containing BaZrO3 inclusions with mean grain size smaller than 1 μm. X-ray diffraction showed single epitaxial relationship between BaZrO3 and YBa2Cu3O7-δ. The effective surface resistance was measured at 47.7 GHz for 60<T<90 K and 0<μ0H<0.8 T. The magnetic field had a very different effect on pristine YBa2Cu3O7-δ and YBa2Cu3O7-δ/BaZrO3, while for μ0H=0 only a reduction of Tc in the YBa2Cu3O7-δ/BaZrO3 film was observed, consistent with dc measurements. At low enough T, in moderate fields YBa2Cu3O7-δ/BaZrO3 exhibited an intrinsic thin film resistance lower than the pure film. The results clearly indicate that BaZrO3 inclusions determine a strong reduction of the field-dependent surface resistance. From the analysis of the data in the framework of simple models for the microwave surface impedance in the mixed state we argue that BaZrO3 inclusions determine very steep pinning potentials.