Rate Of Increase In Resistance Research Articles

Analysis of electrical contact characteristics of strap contacts used in high voltage bushings under eccentric conditions

AbstractThe contact finger electrical connection structure is a crucial component of high voltage bushings, and its safety and reliability directly impact the operational stability of the bushing. To investigate electrical contact performance of the contact finger under eccentric conditions, a three‐dimensional electrical, thermal, and force multi‐physics coupling calculation model was established. Additionally, a test platform was constructed to measure electrical contact characteristics of the contact finger. The contact characteristics of the contact finger when the male head was axially deflected and radially offset compared to the female head were obtained. The research findings indicate when the male head deflects axially, the contact force changes of the contact finger blades on both sides are opposite. Moreover, as the axial deflection angle of the male head increases, the resistance of the electrical connection structure shows a rising‐slow decreasing‐fluctuating trend. The resistance is highest at 3°, with a resistance increase rate of 7.35%. Furthermore, the resistance of the electrical connection structure varies with the radial offset of the male head, following a power function. Contact failure occurs when the radial offset is 1.31 mm, and the resistance increase rate reaches 24.9% at a radial offset of 1.58 mm.

Low-cost, high-density Mn–Co spinel coatings for stainless steel interconnect via efficient microwave heating

The high preparation cost and poor density of spinel coatings for stainless steel interconnect have always been puzzling conundrums for the solid oxide fuel cell stack developers. Herein, the microwave heating technology for fabricating Mn–Co spinel coating is developed to address these issues. We designed a device spontaneously providing reducing atmospheres and realized the low-cost, high-efficiency reduction of Mn–Co spinel via microwave heating. Dense coatings (MnO + Co) are formed on the steel surface at ∼1100 °C. The excellent density is related to the melting of Co particles induced by microwave selective heating. At initial, microwave heating is dominated by dipolar polarization, interfacial polarization, and natural resonance. After forming metallic Co, conductive loss and the lens effect further accelerate the reduction process. High-quality spinel coatings are formed during the subsequent oxidation at 800 °C, exhibiting an extremely low area-specific resistance increase rate.

Impact of the electrode potential of negative electrode on the increase in resistance of LiNi1/2Mn3/2O4 positive electrode

An increase in the resistance of electrode materials due to the formation of electrode/electrolyte interphases (EEI) induces capacity loss and power fading in lithium-ion batteries, and hence, is a significant problem that hinders the extension of battery lifetime. Previous studies have reported that the increase in the resistance of one electrode is affected by the other electrode, suggesting that the crosstalk reaction plays a crucial role in the increase in the resistance of the electrodes. In this study, to understand the resistance increase mechanism in relation to the crosstalk reaction, lithium-ion cells with a LiNi1/2Mn3/2O4 (LNMO) electrode with various materials (Li metal, graphite, Li[Li1/3Ti5/3]O4, and LiFePO4) as a negative electrode were examined via potentiostatic charge tests. The rate of increase in resistance of the LNMO electrodes against capacity due to side reactions depends on the electrode potential of the negative electrode: a lower electrode potential of the negative electrode slows down the rate of increase in resistance of the LNMO electrodes. Based on these results, an explanation for the resistance increase was provided by taking into consideration the crosstalk reaction. The crosstalk reaction reduces the amount of oxidative decomposition products generated at the LNMO electrode by consuming these products at the negative electrode; i.e., the resistance increase by EEI formation is minimized. A cell design based on the proposed mechanism, wherein the lower electrode potential of the negative electrode suppresses the increase in resistance of the positive electrodes, will open up the possibility of batteries with a long life.

Understanding resistance increase in composite inks under monotonic and cyclic stretching

Cyclic degradation in flexible electronic inks remains a key challenge while their deployment in life critical applications is ongoing. The origin of electrical degradation of a screen-printed stretchable conductive ink with silver flakes embedded in a polyurethane binder is investigated under uniaxial monotonic and cyclic stretching, using in-situ confocal microscopy and scanning electron microscopy experiments, for varying ink thickness (1, 2, and 3 layers, each layer around 8–10 μm) and trace width (0.5, 1, and 2 mm). Cracks form under monotonic stretching, and the evolution of crack pattern (density, length and width) with applied strain is affected by ink thickness such that the 3-layer ink exhibits larger normalized resistance but slightly lower resistance than the 1-layer ink up to strains of 125%. For cyclic stretching, the crack density and length do not evolve with cycling. However, the cracks widen and deepen, leading to an increase in resistance with cycling. There exists a strong correlation between fatigue life, i.e. the number of cycles until a normalized resistance of 100 is reached, and the strain amplitude. The normalized resistance increase rate with respect to cycling is also found to scale with strain amplitude. The rate of change in resistance with cycling decreases with ink thickness and trace width. For practical applications, thicker (25 μm) and wider (⩾2 mm) inks should be used to lower resistance increases with repeated deformation.

Assessment of Chemical Fiber Air Filter for General Ventilation

Air filters for general ventilation have mainly been used to control the concentration of indoor particulate matter. In this study, the pressure differential, test dust capacity, quality factor and operating life of class F8 pleat–plate and multi-bag type chemical fiber filters were evaluated using an air filter performance test system. The results showed that the resistance increase rate of multi-bag filter (0.49 Pa/g·(cm/s)) was lower than that of pleat–plate filter (1.94 Pa/g·(cm/s)), the quality factor of the multi-bag filter was lower than that of pleat–plate filter, and the dust capacity of the multi-bag filter was much higher than that of the pleat–plate filter. The operating life of the multi-bag filter was 8 times as that of the pleat–plate filter with the measured PM2.5 of outdoor. The energy consumption of the pleat–plate filter was 2.2 times that of the multi-bag filter. Analyzing the electron microscope photos after dust loading, the dust depth of pleat–plate filter into filter material was thinner than that of multi-bag filter. The research results could provide data support for the design optimization and selection of ventilation filters and the treatment of the particulate matter in indoor environments.

Analysis of Mechanical Properties of Composite Electrode with Different Binder Molecular Weights

In order to improve the energy density of the lithium ion battery, the loading level of the electrode is continuously increasing. As a result, the presence of inactive materials such as conductive materials / binders in the electrodes is also highlighted. In particular, securing the mechanical properties of the electrode according to the distribution and composition of the binder is becoming more important in terms of long-term reliability. However, increasing the composition of the binder of the electrode can ensure the mechanical properties of the electrode at the same loading level and density, but increases the resistance of the electrode. This increase in resistance may reduce the lifetime of the electrode, apart from the mechanical properties of the electrode. Therefore, in order to minimize the resistance increase rate of the electrode and to secure mechanical properties, the mechanical properties and resistance of the electrode according to the molecular weight of the binder in the electrode were analyzed.In this presentation, three LiCoO2 electrodes with different PVDF binder molecular weights of 500,000 / 630,000 / 1,000,000 were prepared, and the adhesion and volume resistivity of the electrodes were measured using SAICAS and Electrode Resistance Meter. Although the adhesion of the electrodes was different according to the molecular weight of the PVdF binder, the increase in the volume resistivity of the electrode was not large. This is because the behavior of the binder and the active material / conductive material in the electrode are different from each other as the molecular weight of the binder increases, and the mechanical properties of the binder are also different according to the molecular weight. In order to confirm this more intuitively, the battery was fabricated and the behavior of the electrode was observed. Furthermore, the physical properties of the polymer were analyzed according to the molecular weight of the binder in order to clarify the cause.

A Study on Copper/Silver Core–Shell Microparticles with Silver Nanoparticles Hybrid Paste and its Intense Pulsed Light Sintering Characteristics for High Oxidation Resistance

In this study, a silver (Ag) coated copper (Cu) core–shell microparticles paste were fabricated and screen-printed on Polyimide (PI) substrates. It was sintered via intense pulsed light (IPL) sintering technique. IPL irradiation condition (i.e. pulse duration, irradiation energy) was optimized to obtain high conductivity and good oxidation resistance characteristics. To increase the packing density of the pastes and its oxidation resistance, Ag nanoparticles (Ag NPs) were added to Cu/Ag core–shell microparticles (core–shell MPs) paste with optimal mass ratio. To analyze the sintering and oxidation characteristics of hybrid pastes (Ag NPs + core–shell MPs), a scanning electron microscope (SEM) and a focused ion beam (FIB) was used. To demonstrate the mechanism of the sintering process on hybrid pastes, heat generation at the junctions between particles were simulated using Multiphysics COMSOL program. The packing density of the hybrid pastes was investigated using CATIA digital mock-up (DMU) program. In addition, to confirm the heat generation with respect to the packing density of the hybrid pastes, in-situ temperature monitoring process was conducted. As a result, hybrid paste pattern sintered with IPL showed excellent oxidation resistance (resistance increase rate in 300 °C for 5 h: 4.92%), and high electrical conductivity (6.54 μΩ cm).

A Study on Corrosion Resistance of Electroplated Gold over Nanocrystalline Ni-W for Contact Applications

Highly conductive metal with least corrosion resistance is the most prominent requirement of contact industries. Although deposition of gold over Ni sulfamate is a standard interface for contact and connector applications, the performance of gold over Ni sulfamate has faced several problems such as wear durability, porosity of gold layers and biased corrosion resistance. The deposition of nanocrystalline Ni-W (nc Ni-W) between gold and Ni sulfamate improves the mechanical and surface properties of interfaces. In this work two different types of samples were processed and compared in terms of corrosion. The first sample (Au/NiSO4) was prepared using electroplating of gold, Ni sulfamate and Ni strike over base material of copper alloy with thicknesses of 0.9 µm, 1.9 µm and 0.5 µm respectively. In the second sample (Au/nc Ni-W/NiSO4), all layers of electroplating were same except the addition of 1.8 µm of nanocrystalline Ni-W before deposition of gold. Both samples were passed through the environments of (a) 85% relative humidity at 85oC for 24 hours, (b) 85% relative humidity at 85oC for 96 hours and (c) nitric acid vapors for 60 minutes. The effect on electrical, mechanical and materials properties of samples were investigated before and after passing through these environments using Force Deflection Resistance (FDR), Life-cycle test (LCT), Scanning electron microscopy (SEM), Energy dispersive spectroscopy (EDS) and X-Ray CT scanning. Although Au/NiSO4 is a well-known interface for connector applications [1], the deposition of nc Ni-W between gold and NiSO4 reduces the rate of corrosion because nc Ni-W has a weak tendency for grain boundary segregation and building broader range of accessible grain sizes [2]. There is formation of grain colonies in Ni-W deposit which controls crack propagation and corrosion [3]. The performance of two different interfaces of Au/NiSO4 and Au/nc Ni-W/ NiSO4 against corrosion was tested after electroplating on spring probes. Spring probe is one of the product of Smiths Interconnect which is used for different applications like defense, medical, rail, semiconductor, space etc. [4]. In FDR, the spring force, coefficient of friction and contact resistance was measured under a hysteresis of compression and extension for a travel distance of 0.14 inch. In the case of Au/NiSO4, the difference in compression and extension force at 0.14 inch was 6.1 oz. In the case of Au/nc Ni-W/ NiSO4, this difference was 4.6 oz which means that there is less friction with the deposition of nanocrystalline Ni-W underneath gold. Moreover, the difference in contact resistances was lower in second sample which means that the addition of nc Ni-W enhances the interface of gold and NiSO4. After treatment in humidity from 24 hrs to 96 hrs the difference in compression and extension force at 0.14 inch was increased by 7 oz in first sample but in second sample this difference was only increased by 3.6 oz which means that there is less increase in friction due to the presence of nc Ni-W. In LCT the resistance was measured at a test current of 0.025 amps under a stroke length of 0.09 inch for 10,000 life cycles with a cycle rate of 4 cycles/sec. The rate of increase in resistance with number of cycles was higher in the case of Au/NiSO4 than Au/nc Ni-W/ NiSO4. In first sample, the sticky coefficient was increased from 0 to 25 % after treatment in humidity for 24 hrs and it further increased to 37.5% after keeping in humidity for 96 hrs. The wear off rate and friction reduction of Au/nc Ni-W/ NiSO4 helped in maintaining the sticky coefficient to be constant even after kept in humidity for 96 hrs. The failure of the probes were tested from front and cross section SEM, point and line scan EDS and X-Ray CT scanning. SEM was used to observe mechanical marks and microstructure analysis which explained the reasoning of low wear rate in the case of Au/NiSO4. The failure of the probes was also confirmed from X-Ray CT Scanning in the probes during compression of spring. The complete set of experimental results will be added in the full version of the paper.

Degradation analysis of dead-ended anode PEM fuel cell at the low and high thermal and pressure conditions

In this study, it is demonstrated that operation of dead-ended anode fuel cell at high temperature and pressure reduce the durability of membrane electrode assembly. In such a way that after 9000 degradation cycles, the maximum power density under H2/O2 gas feed mode for the aged MEA at high temperature and pressure is dropped by 38.8%. While the maximum power density drop is 27.1% for the aged MEA at low temperature and pressure. Comparison of the electrochemical impedance spectroscopy responses of MEAs shows that during aging process, the charge transfer resistance increase rate is more at higher temperature and pressure. This suggests the more severe destruction of catalyst layer at higher temperature and pressure and is in agreement with the obtained values of electrochemical surface area from the cyclic voltammetry test. In addition, the transmission electron microscopy and scanning electron microscopy images show the further degradation of cathode catalyst layer and more sever Pt agglomeration at higher temperature and pressure.

Application of Additional Coating for Conductive Yarns Protection against Washing

The conductive yarn is an essential component of the smart textile making the product light and comfortable to wear. Nevertheless, one of the most common problems is care that limits the use of the product. Application of additional coating to the yarn renders it water-repellent properties and allows reduction of the negative impact of water on its performance. During the research additional coatings were applied to conductive yarns, with the aim of minimizing electrical resistivity changes caused by washing cycles. Two types of coatings were applied to the yarns, they were washed and tested. The article describes changes in the electrical resistance of different conductors depending on the linear density of the yarn, the type of coating applied and the number of washing cycles. The electrical resistance of electrically conductive yarns increases with washing until they become non-conductive. The electrical resistance of non-textured yarns increases more slowly and the smaller increase is observed in thick yarns. The water-repellent silicone coating applied to yarns reduces the electrical resistance increase rate and the yarns retain their conductivity over more washing cycles.

Fabrication of high-performance graphene nanoplatelet-based transparent electrodes via self-interlayer-exfoliation control.

Graphene nanoplatelets (GNP) have attracted considerable attention due to their high yield and fabrication route that is scalable to enable graphene production. However, the absence of a means of fabricating a transparent and conductive GNP film has been the biggest obstacle to the replacement of pristine graphene. Here, we report on a novel means of fabricating uniform and thin GNP-based high-performance transparent electrodes for flexible and stretchable optoelectronic devices involving the use of an adhesive polymer layer (PMMA) as a GNP layer controller and by forming a hybrid GNP/AgNW electrode embedded on PET or PDMS. Relative to the commercially available indium tin oxide (ITO) film on a PET substrate, a GNP-based electrode composed of hybrid GNP/AgNW on PET exhibits superb optical, physical, and electrical properties: a sheet resistance of 12 Ω sq-1 with 87.4% transmittance, a variable work function from 4.16 to 5.26 eV, an ultra-smooth surface, a rate of resistance increase of only 4.0% after 100 000 bending cycles, stretchability to 50% of tensile strain, and robust stability against oxidation. Moreover, the GNP-based electrode composed of hybrid Cl-doped GNP/AgNW shows outstanding performance in actual organic light-emitting diodes (OLEDs) by exhibiting an increased current efficiency of 29.5% and an increased luminous efficiency of 36.2%, relative to the commercial ITO electrode on PET.

Lubricating property of cast iron combined with two-scale unit structure by biomimetic laser treatment

Abstract A damaged surface with a residual hardened layer was observed on a failure guide surface. Using a two-step laser treatment, a two-scale unit structure with a different spacing was distributed on the failure surface to form a biomimetic surface to recover its property/function. A theoretical equation describing the relationship between the wear resistance increase rate of biomimetic samples and the spacing between units was formulated in this study. In addition, finite element (FE) method was used to analyze the lubricating property of biomimetic surface and the effect of the distribution of units on the sliding wear resistance. Moreover, the dynamic cycle wear process of the biomimetic surface similar to the flexion and extension movement of earthworms in soil was analyzed.

Integrated membrane and microbial fuel cell technologies for enabling energy-efficient effluent Re-use in power plants

Municipal wastewater is an attractive alternative to freshwater sources to meet the cooling water needs of thermal power plants. Here we offer an energy-efficient integrated microbial fuel cell (MFC)/ultrafiltration (UF) process to purify primary clarifier effluent from a municipal wastewater treatment plant for use as cooling water. The microbial fuel cell was shown to significantly reduce chemical oxygen demand (COD) in the primary settled wastewater effluent upstream of the UF module, while eliminating the energy demand required to deliver dissolved oxygen in conventional aerobic treatment. We investigated surface modification of the UF membranes to control fouling. Two promising hydrophilic monomers were identified in a high-throughput search: zwitterion (2-(Methacryloyloxy)-ethyl-dimethyl-(3-sulfopropyl ammoniumhydroxide, abbreviated BET SO3−), and amine (2-(Methacryloyloxy) ethyl trimethylammonium chloride, abbreviated N(CH3)3+). Monomers were grafted using UV-induced polymerization on commercial poly (ether sulfone) membranes. Filtration of MFC effluent by membranes modified with BET SO3− and N(CH3)3+ exhibited a lower rate of resistance increase and lower energy consumption than the commercially available membrane. The MFC/UF process produced high quality cooling water that meets the Electrical Power Research Institute (EPRI) recommendations for COD, a suite of metals (Fe, Al, Cu, Zn, Si, Mn, S, Ca and Mg), and offered extremely low corrosion rates (<0.05 mm/yr). A series of AC and DC diagnostic tests were used to evaluate the MFC performance.

Neonatal bloodstream infections in a Ghanaian Tertiary Hospital: Are the current antibiotic recommendations adequate?

BackgroundDiagnosis of bloodstream infections (BSI) in neonates is usually difficult due to minimal symptoms at presentation; thus early empirical therapy guided by local antibiotic susceptibility profile is necessary to improve therapeutic outcomes.MethodsA review of neonatal blood cultures submitted to the microbiology department of the Korle-Bu Teaching Hospital was conducted from January 2010 through December 2013. We assessed the prevalence of bacteria and fungi involved in BSI and the susceptibility coverage of recommended empiric antibiotics by Ghana Standard Treatment guidelines and the WHO recommendations for managing neonatal sepsis. The national and WHO treatment guidelines recommend either ampicillin plus gentamicin or ampicillin plus cefotaxime for empiric treatment of neonatal BSI. The WHO recommendations also include cloxacillin plus gentamicin. We described the resistance profile over a 28-day neonatal period using multivariable logistic regression analysis with linear or restricted cubic splines.ResultsA total of 8,025 neonatal blood culture reports were reviewed over the four-year period. Total blood culture positivity was 21.9 %. Gram positive organisms accounted for most positive cultures, with coagulase negative staphylococci (CoNS) being the most frequently isolated pathogen in early onset infections (EOS) (59.1 %) and late onset infections (LOS) (52.8 %). Susceptibility coverage of early onset bacterial isolates were 20.7 % to ampicillin plus cefotaxime, 32.2 % to the combination of ampicillin and gentamicin, and 71.7 % to cloxacillin plus gentamicin. For LOS, coverage was 24.6 % to ampicillin plus cefotaxime, 36.2 % to the combination ampicillin and gentamicin and 63.6 % to cloxacillin plus gentamicin. Cloxacillin plus gentamicin remained the most active regimen for EOS and LOS after exclusion of BSI caused by CoNS. For this regimen, the adjusted odds of resistance decreased between 12-34 % per day from birth to day 3 followed by the slowest rate of resistance increase, compared to the other antibiotic regimen, thereafter until day 28. The trend in resistance remained generally unchanged after excluding data from CoNS. Multidrug resistant isolates were significantly (p-value <0.001) higher in LOS (62.4 %, n = 555/886) than in EOS (37.3 %, n = 331/886).ConclusionsThere is low antibiotic susceptibility coverage for organisms causing neonatal bloodstream infections in Korle-Bu Teaching Hospital when the current national and WHO recommended empiric antibiotics were assessed. A continuous surveillance of neonatal BSI is required to guide hospital and national antibiotic treatment guidelines for neonatal sepsis.Electronic supplementary materialThe online version of this article (doi:10.1186/s12879-016-1913-4) contains supplementary material, which is available to authorized users.

Frequency of Multidrug-Resistant Organisms Cultured From Urine of Children Undergoing Clean Intermittent Catheterization.

Children undergoing CIC frequently have positive urine culture results and receive many antimicrobial agents. Subsequently, this population is at high risk for infections caused by antimicrobial-resistant bacteria. Resistant pathogens, such as vancomycin-resistant Enterococcus (VRE), carbapenem-resistant Enterobacteriaceae (CRE), and organisms that produce extended-spectrum β-lactamases (ESBLs), which are third-generation cephalosporin resistant (3GCR), are of particular concern. In this retrospective study, all urine culture results and antimicrobial-susceptibility testing results were obtained between January 2008 and December 2014 from the electronic health record of children ≤18 years of age who were undergoing CIC (n = 14 832). Isolates were identified as VRE, CRE, or 3GCR. Organisms of the same type that were obtained in the same year and with identical antibiotic susceptibilities from the same patient were excluded. Simple linear regression was used to determine the association between year and rates of resistance. A total of 3997 positive culture results were included in this analysis. Of all Enterococcus isolates for which susceptibility results were available, 4.6% were VRE, 11.1% of all isolates that belonged to the Enterobacteriaceae family were 3GCR, and 0.4% of eligible isolates were CRE. There were significantly higher rates of resistance to third-generation cephalosporins and CRE in 2014 than in 2008 (P < .01). Simple linear regression revealed a significant association between year and rate for resistance to third-generation cephalosporins but not for CRE or VRE. The rate of increase in resistance to third-generation cephalosporins in patients who required CIC was higher than that in patients who did not need CIC. The rate of resistance to third-generation cephalosporins has increased significantly in the past 7 years in children undergoing CIC, which indicates that careful monitoring is warranted for continued increases in antimicrobial-resistant organisms in this unique patient population.

Strain-dependent electrical resistance of epoxy/MWCNT composite after hydrothermal aging

Abstract The electrical resistance of epoxy/multi-wall carbon nanotube (MWCNT) composites was studied under the effect of hygro- and hydrothermal aging. Tensile tests were conducted and the responses in the electrical resistance were measured during the tests for samples with different prehistory of environmental exposure. The overall pattern of the electrical resistance change versus strain for the samples tested consists of linear and nonlinear regions with a broad peak that precedes the ultimate strength of the sample and occurs at the onset of evident plastic deformation in the stress–strain curve. The composite with lower content of MWCNTs exhibits a more pronounced nonlinear behavior and the rate of resistance increase with strain is significantly higher that is attributed to a dominant role of the tunneling-type resistance. Moisture and water uptake of the samples resulted to an increase of their electrical resistance. This fact is explained by the increased tunneling resistance due to epoxy swelling and hydrothermally-induced structural variations of the MWCNT conductive network. Samples conditioned under different hygro- and hydrothermal conditions show different strain-dependent response of the electrical resistance, which is not directly related to the level of moisture/water uptake. Under low strain values, strain sensing functionality of epoxy/MWCNT composites is only slightly affected by aging conditions.

Long-term Steam Electrolysis with Electrolyte-Supported Solid Oxide Cells

Steam electrolysis over 11000h11The test was still running at the time of submission of the revised work, exceeding 14 000 h operation time. with an electrolyte-supported solid oxide cell is discussed. The cell of 45cm2 area consists of a scandia/ceria doped zirconia electrolyte (6Sc1CeSZ), CGO diffusion-barrier/adhesion layers, a lanthanum strontium cobaltite ferrite (LSCF) oxygen electrode, and a nickel steam/hydrogen electrode. After initial 2500h operation with lower current-density magnitude, the current density was set to j=-0.9Acm−2 and the steam conversion rate to 51%. This led to a cell voltage of 1.185V at 847°C cell temperature. Average voltage degradation was 7.3mV/1000h (<0.6%/1000h), the increase in the area specific resistance was 8mΩcm2/1000h, sufficiently low for application in practical electrolysers. The electrical-to-chemical energy-conversion efficiency was ηel>100% throughout the test (with an external heat source for evaporation). Impedance spectroscopic measurements revealed a degradation almost entirely due to increasing ohmic resistance. The rate of resistance increase was initially faster (up to 40mΩcm2/1000h) and stabilised after several 1000h operation. After 9000h a small (non-ohmic) electrode degradation became detectable (<2mV/1000h), superimposed to ohmic degradation. The small electrode degradation is understood as indication for largely reversible (electrolysis cell/fuel cell) behaviour.

Tuning the Electrical and Optical Properties of Graphene by Ozone Treatment for Patterning Monolithic Transparent Electrodes

Tunable electrical and optical properties of graphene are vital to promote its use as film electrodes in a variety of devices. We developed an etching-free ozone treatment method to continuously tune the electrical resistance and optical transmittance of graphene films by simply varying the time and temperature of graphene exposure to ozone. Initially, ozone exposure dramatically decreases the electrical resistance of graphene films by p-doping, but this is followed by increases in the resistance and optical transmittance as a result of surface oxidation. The rate of resistance increase can be significantly increased by raising the treatment temperature. The ozone-oxidized graphene is not removed but is gradually transformed to graphene oxide (GO). On the basis of such effects of ozone treatment, we demonstrate a well-defined graphene pattern by using ozone photolithography, in which the ozone-treated graphene electrodes are monolithic but separated by insulating GO regions. Such a monolithic graphene pattern shows low optical contrast, a clean and more hydrophilic surface, indicating the promising use of ozone treatment to achieve high-performance graphene-based optoelectronic devices.

Life testing of LSM–YSZ composite electrodes under reversing-current operation

Durability testing of solid oxide cell electrodes in reversing-current and constant-current operation modes is presented. (La0.8Sr0.2)0.98MnO3-δ-Zr0.84Y0.16O2-γ (LSM-YSZ) symmetric cells were tested at 800 °C in air with current densities of 0.5 and 1.5 A cm(-2), with current cycle periods of 1 and 12 h. A continuous increase in both ohmic and polarization resistance was observed, via Electrochemical Impedance Spectroscopy (EIS), for cells tested with a reversing current of 1.5 A cm(-2), whereas cells tested at 0.5 A cm(-2) showed no measurable resistance increase. The resistance degradation was explained by delamination in the electrode, observed by post-test Scanning Electron Microscopy (SEM), near the interface with the electrolyte for the 1.5 A cm(-2) cells, but not for those tested at 0.5 A cm(-2). Current cycle period also impacted the degradation observed at 1.5 A cm(-2): both the rate of resistance increase and the extent of post-test delamination decreased on going from constant current mode to a 12 h period to a 1 h period. The results indicate that lower current densities and reversing-current operation are desirable to maximize the lifetime of solid oxide cells.

The resistance ratchet: theoretical implications of cyclic selection pressure

To investigate the effects of cyclic antibiotic selection pressure on resistance in a simple mathematical model. The model assumed that resistance in microbial ecologies changes slowly with changing selection pressure, at a rate proportional to the difference between the current resistance level and the resistance level that would be in equilibrium with current selection pressure. The maximum rate of increase in resistance during periods of increasing selection was assumed to be greater than the maximum rate of decrease during decreased selection. Under a simulated annual cyclic selection pressure variation of 40%, with maximum resistance rise and fall rates of 10 and 0.5%, respectively, resistance rose above the level expected from the mean selection pressure by small ratchet-like increments. Over 50 simulated years, resistance increased to 62%, rather than the 50% expected from the mean level of selection. Welsh community prescribing for a selection of antibiotics showed a seasonal cyclic variation of 13-45%. The intuitive assumption that cyclic selective pressure would produce resistance levels commensurate with the mean selection pressure was contradicted; rather resistance drifted towards a level commensurate with maximum selection pressure. If the ratchet effect exists in reality, it may produce unexpected excess resistance, particularly in the community for antibiotics used in respiratory infection, where cycling is pronounced, or in ITU antibiotic rotation. It should be most pronounced for resistance systems with strong asymmetry between rates of adaptation under rising and falling selection pressure. Non-linear dynamic systems in physics and ecology are notorious for producing counter-intuitive effects; resistance epidemiology may be similar.