Rate Of Conductance Change Research Articles

Strain controlling transport properties of heterostructure composed of monolayer CrI3

The modulation of the magnetic state and spin orientation in two-dimensional (2D) intrinsic magnets is important for controlling the spin-dependent transport properties of 2D magnet-based heterostructures. In this work, using first-principles calculations, it is found that the Néel antiferromagnetic (AFM) state with in-plane spin and the ferromagnetic (FM) state with in-plane and out-of-plane spin can be achieved in monolayer CrI3 under appropriate in-plane strains. In particular, the conductance of the Graphite/monolayer-CrI3/Graphite van der Waals heterostructure increases with the increase in the tensile strain, and the rate of change in conductance reaches more than 1800% when the strain becomes larger than 20%, which is significantly larger than that of the van der Waals heterostructure with a nonmagnetic insulator as a barrier to the magnetic field. Interestingly, when the magnetic state in monolayer CrI3 is switched from the Néel AFM to FM state by strain, the anisotropy magnetoresistance (AMR) ratio of the Graphite/monolayer-CrI3/Graphite heterostructure changes from −34.8% to 70%. The changes of AMR and conductance with strain originate mainly from the variation of the bandgap of monolayer CrI3 and the average transmission channels of graphite. These findings enrich the method in tuning spin orientation and provide the route for controlling transport properties of the heterostructure by strain tuning spin orientation in 2D magnets.

Research on MPPT Based on Fuzzy Auto-disturbance Rejection

For the classical maximum power point tracking algorithm, the setting of small step increases the speed of maximum power tracking of photovoltaic power generation system and the stability of operation in stable state. To solve this problem, this paper designs a maximum power point tracking system based on booster circuit, and adopts fuzzy auto-disturbance rejection control to improve the conductance increment method with variable step length. Based on the relationship between the rate of conductance change and the maximum power point conductance, the step size of the adrc is adjusted by using the fuzzy logic control. The MPPT system of photovoltaic power generation is designed by combining the incremental conductance method and the improved fuzzy control method with the correction factor. The control method does not depend on the mathematical model of the system, the design is flexible, the control effect is robust, stable and accurate. It can be used for reference for other types of solar photovoltaic power generation control system.

Study of the Effect of Rock Type and Treatment Parameter on Acid Fracture Conductivity Using an Intelligent Model

One of the fundamental ways to stimulate and increase the production rate of a well completed in a carbonate reservoir is acid fracturing. The amount of rock dissolved, fracture surface etching patterns, rock strength, and closure stress impacts the conductivity of the resulting acid fracture. A model of acid fracturing conductivity must accurately anticipate fracture conductivity versus closure stress. There are two parts for an acid fracture model: fracture conductivity at zero closure stress and the rate of conductivity change with closure stress. The fracture conductivity is substantially influenced by rock type. A serious challenge in recent studies has been to predict behaviour of different formations under various closure stresses. Furthermore, treatment parameters like acid injection rate and acid strength have different effects on fracture conductivity, depending on formation type. This study develops artificial neural network models to precisely predict fracture conductivity by incorporating experimental data from various formations, thereby resulting in a good match between model predictions and experimental data. The effects of rock type and treatment parameters on fracture conductivity are investigated and show that different formations have different responses under various closure stresses. There is an optimum point at which maximum fracture conductivity is achieved, but finding this point is difficult because it is distinct for different formations.

Real-time monitoring of scale formation in reverse osmosis using electrical impedance spectroscopy

Early detection of scale formation in reverse osmosis systems remains challenging since the bulk measurements of the operating data are not sufficiently sensitive to detect the subtle changes occurring across the membrane. Electrical impedance spectroscopy (EIS) was investigated as a tool for measuring the electrical properties in real time and to identify changes that occur during calcium sulfate scaling in a reverse osmosis system. EIS signals were obtained across a frequency range of 10−1–105Hz during the filtration of calcium sulfate scale forming constituents in recirculation and batch modes. The measured capacitance and conductance of various electrically distinct layers were compared against the flux measurements, in order to assess their significance to indicate the scale formation. The rate of change in conductance was higher than the flux decline. Change in the conductance value around 38Hz, corresponding to the coating layer on the active membrane surface was most suitable. From the suggested approach of monitoring the changes in conductance at 10–100Hz, scale formation can be detected prior to observing any significant permeate flux decline.

New Correlations of Acid-Fracture Conductivity at Low Closure Stress Based on the Spatial Distributions of Formation Properties

Summary Because of irregular fracture surfaces caused by heterogeneities such as variations in local mineralogy and variations in leakoff behavior, we use a correlation to calculate fracture conductivity in acid fracturing. An acid-fracture-conductivity correlation consists of two parts: conductivity at zero closure stress and the rate of conductivity change with closure stress. Existing correlations do not consider the effect of variations in formation properties and were developed on the basis of laboratory experiments that use core samples with dimensions of only a few inches. On the other hand, acid-fracture simulators have grid sizes of several feet to tens of feet. Therefore, correlations should be scaled up properly when used in a fracture simulator. This paper presents new correlations to obtain the conductivity at zero closure stress. This conductivity can then be incorporated in acid-fracture-conductivity models that consider the effect of closure stress. In this study, an extensive numerical study was performed using an intermediate-scale acid-fracture model with total dimensions comparable to a gridblock size in an acid-fracturing simulator and grid sizes comparable to core-sample sizes used in laboratory acid-fracture-conductivity tests. In this model, the distributions of permeability and mineralogy along the fracture faces are geostatistically generated. The model generates fracture-surface-etching profiles as a function of acid contact time, from which we can obtain fracture-width distributions when the fracture surfaces have come in contact at low closure stress. We then calculate the fracture conductivity by solving for the flow rate through this irregular domain for a fixed ∆p across the domain. By analyzing the relationship between the fracture conductivity created and statistical properties of the permeability and mineralogy distributions, we developed new acid-fracture-conductivity correlations for low closure stress. These correlations can be used directly to better predict the primary coefficient in the widely used Nierode-Kruk (Nierode and Kruk 1973) correlation of acid-fracture conductivity. This work allows the Nierode-Kruk (N-K) correlation to be scaled up to the dimensions appropriate for use in an acid-fracturing simulator.

Use of indirect conductimetry to predict the growth of spoilage yeasts, with special consideration of Zygosaccharomyces bailii

In recent years, modeling for the purpose of predicting microbiological spoilage of foods has gained much interest. Predictive modeling requires a concentrated mathematical and experimental approach; to collect data of adequate quality is a technically demanding task when several experimental parameters are involved. Rapid, non-traditional, automated techniques are particularly useful in modeling. Of these, electrometric techniques appear to be most promising. Indirect conductimetry was used to study the effect of temperature, a w, automated Malthus 2000 instrument proved to be convenient for gathering a large amount of data that were then used to develop polynomial models describing the response of the yeasts to combinations of experimental factors in terms of conductimetric detection time and maximum rate of change in conductance. Results demonstrated that indirect conductimetry is suitable for monitoring the effect of environmental factors on the growth and activity of Z. bailii and perhaps other food spoilage yeasts.

Conductance measurements for data generation in predictive modeling

The electrical resistance of a growth medium inoculated with bacteria may be automatically recorded throughout an incubation period without the necessity for sampling. The rate of change in conductance is dependent on the bacteria studied, the medium composition and the prevailing growth conditions. The effect of growth medium composition, growth conditions and inoculum level on the conductance response was studied forYersinia enterocolitica O:3. A large number of combinations of factors affecting the growth/activity of the bacteria could be studied simultaneously due to the large instrumental capacity of the Malthus 2000. A polynomial model based on conductance measurements was developed forY. enterocolitica describing the effect of temperature, pH andl-lactate level on conductance response curve parameters. The model was used for predicting growth rates. Growth rates calculated from bacterial counts ofY. enterocolitica growing in minced pork corresponded to growth rates predicted using the polynomial conductance models.

Evaluation of the indirect conductance method for the detection of yeasts in laboratory media and apple juice

The technique of indirect conductimetry was examined to asses growth of seven yeast species (Candida glabrata, C. parapsilosis, Debaryomyces hansenii, Pichia membranaefaciens, Rhodotorula glutinis, Saccharomyces cerevisiae, Zygosaccharomyces bailii) in terms of detection time, maximum rate of change in conductance and maximum change in conductance in laboratory media and apple juice. Conductance parameters were dependent on the species, population density, temperature, pH, aw and potassium sorbate concentration. Indirect conductimetry can be applied to detect yeasts at populations as low as 101 cfu ml-1 within 48 h at 30°C. A defined medium is not required to enhance conductivity. Measurements can be done directly in apple juice without interference of juice constituents with conductance signals. Compared to direct conductimetry, the indirect method is more sensitive, giving shorter detection times and higher rates of change in conductance. Conductance responses measured by the indirect method correlated well with viable yeast populations determined by conventional plate count techniques. Indirect conductimetry has potential as a rapid, convenient and reliable method to evaluate product quality and stability, and it may also have application in developing model systems to predict shelf-life of foods subject to yeast spoilage.

Effect of protamine sulfate on the permeability properties of the mammalian urinary bladder

Protamine sulfate (PS, an arginine-rich protein of molecular weight 5,000) has been reported to affect the ionic permeability of gallbladder epithelium, the permeability of cultured epithelial cells to mannitol, and the permeability of endothelial cell layers to albumin. Although the effect of PS has been widely investigated, the mechanism of its action on membrane permeability is presently unknown. The effect of PS on the rabbit urinary bladder epithelium was studied using both transepithelial and intracellular microelectrode techniques in conjunction with equivalent circuit analysis. The addition of 100 micrograms/ml of PS to a NaCl-containing mucosal solution caused (over a 40-min period) a large increase in the transepithelial conductance (Gt) and a transient hyperpolarization of the transepithelial voltage (Vt) followed by a depolarization of Vt. This secondary depolarization of Vt was not present if the mucosal solution was a KCl or a K-gluconate Ringer. The PS-induced increase in Gt was due to an increase in the apical membrane permeability to both cations (Na+ or K+) and anions (Cl- or gluconate). Further studies revealed the following features of the PS-induced conductance. (i) Trypsin inhibits the PS effect; however, this was due to PS hydrolysis by trypsin and not a membrane effect. (ii) Mucosal PS partially inhibited the PS-induced apical membrane conductance. (iii) The ability of PS to increase the membrane conductance was enhanced when the apical membrane potential was cell interior negative. (iv) The rate of conductance change (at any given membrane potential) was a saturating function of the PS concentration. This finding suggests that PS must interact with a membrane binding site before it can induce a change in the membrane conductance. (v) Lanthanum inhibited the PS-dependent conductance by two different mechanisms. One was as a reversible blocker of the PS-induced conductance. The other was by inhibiting the interaction between PS and a membrane binding site. A kinetic model is developed to describe the steps involved in the increase in membrane conductance.

Electrical conductivity of ion-irradiated carbon†

Amorphous carbon films have been irradiated with Cl-ions with energies between 1 and 40 MeV, and the electrical conductivity of the material has been measured as a function of the ion dose. The room temperature conductivity is increased by nearly three orders of magnitude and saturates at a dose of about 10^(15)cm^(−2). The rate of conductivity change vs the ion energy can be explained by an ion track model. The temperature dependence of the conductivity between 100 and 300 K at low doses is in accordance with variable range hopping with a temperature exponent of 1/2. Hopping sites are assumed to be graphite rings or microcrystallites. At higher doses the variable range hopping is replaced by a metallic conductivity with a linear dependence on the temperature similar to that of polycrystalline graphite. This is probably due to the formation of complete percolation paths through the material by interconnection of the graphite regions. Estimates of the size of the crystallites, the hopping activation energy, and the cross section for producing crystallites in the material have been extracted.

Leaf Conductance and Osmoregulation of Field‐grown Sorghum Genotypes1

The relationship between stomatal activity and leaf water potential components was examined for several sorghum [Sorghum bicolor (L.) Moench] genotypes as a function of growth stage under semi‐arid field conditions. During vegetative development, prior to flowering, genotypic differences were observed in the leaf water potential required to initiate stomatal control of transpirational water loss and the rate of change in conductance per unit change in leaf water potential. No significant genotypic differences existed in conductance when leaf water potential was high. After flowering and attainment of maximum leaf size, conductance remained high even when the leaf water potentials declined to −24 to −26 bars.The relationships between leaf water potential components were examined to help explain the leaf conductance observations. Genotypic differences were observed in the leaf water potential‐leaf turgor potential relationships at each growth stage. Prior to flowering, as leaf water potential declined, leaf turgor declined accordingly with little evidence of osmoregulation, and all genotypes reached calculated 0 turgor at essentially the same leaf water potential (−18 to −20 bars). Genotypic differences were also observed in the leaf turgor‐stomatal conductance relationships.After flowering, during the grain filling stage, significant genotypic differences were observed in the degree of osmotic adjustment. The genetic range in osmotic adjustment represents a potentially important adaptive mechanism to water stress which allows for maintenance of turgor and thus of metabolic functions dependent on turgor. Apparently, water conservation through stomatal control is practiced to some extent in sorghum prior to the onset of reproductive development; however, after flowering photosynthetic productivity is apparently maintained at the expense of water conservation.

The decline of potassium permeability during extreme hyperpolarization in frog skeletal muscle.

1. The voltage-clamp technique was used to separate the effects of K depletion in the T-system from the decline in K permeability during hyperpolarization, and to characterize the time- and voltage-dependence of the latter.2. K permeability due to the inward rectifier can be described as being proportional to a parameter which diminishes when the membrane is hyperpolarized beyond -120 mV. The parameter obeys first-order kinetics. At 24 degrees C, it can change with a time constant of 49 msec at -150 mV and 25 msec at -65 mV. At -200 mV the fall in membrane conductance due to the permeability change is to 30% of its initial value. The Q(10) for the rate of conductance change at that potential is about 2.8.3. It is estimated that K inward current can lower the average K concentration in the T-system by more than 50%, and that, on the average, the space enclosed by the T-system should be less than 0.8% of the fibre volume. Assuming the T-system space to be 0.3% of the fibre volume, it is calculated that on the average, and during hyperpolarization to about -150 mV, no more than 20% of the initial current should flow across the surface membrane.

Reactively sputtered tantalum thin film resistors Part 2. Low energy, low fluence proton radiation damage

Tantalum thin film resistors which were reactively sputtered in oxygen and nitrogen simultaneously were bombarded with 150 keV protons to obtain the conductance-fluence characteristics. The conductance of heat treated films increased as a linear function of fluence at room temperature, for values of fluence up to the measured value of 10 16 p/cm 2. This linear conductance increase may be accounted for by radiation-produced defect levels within the intergranular crystalline oxide regions of the discontinuous films. The rate of conductance change with fluence was a maximum for a total reactive partial pressure in the range of 2 × 10 -5 torr, falling off for both greater and smaller total reactive partial pressures. For non heat treated films, the conductance increased as a non-linear function of fluence. This non-linear increase may be accounted for by defect trapping within the amorphous inter-granular oxide. The damage rate as a function of proton beam energy followed the Rutherford law over the range of 50 keV to 150 keV.

The effects of additives in ferric oxide catalysts: I. Electrical measurements and electron probe microanalysis on Mg-doped ferric oxide

Catalysts prepared from high-purity ferric oxide (normally weakly n-type) by incorporating 0.01–2.0 at. % Mg showed p-type semiconducting properties. The catalysts were characterized by electrical measurements and by electron probe micro analysis. The variation of dc conductivity with temperature showed three well-defined regions including a plateau between 450 and 900 °C. From a semiquantitative description of the mixed conduction system a linear relationship is expected between conductivities in the plateau region and the number of Mg 2+ incorporated, and this applied up to 0.1–0.2% Mg. Seebeck voltages showed that each Mg 2+ introduced one p-carrier up to a limit of 0.2% Mg, beyond which anomalies again appeared, although catalysts were still p-type. Electron probe microanalysis provided clear evidence for the separation of the spinel phase, magnesium ferrite, in catalysts containing as little as 0.2% Mg confirming conclusions drawn from the electrical measurements (in air). A special study was made into the effects of firing temperature (to induce Mg incorporation) on the Seebeck voltage in ferric oxide catalysts with 0.3 or 0.5% Mg, i.e., just beyond the critical doping level. Catalysts pellets exposed to the standard reaction mixture used for methanol conversion, or to methanol + argon mixtures, showed a large decrease in conductivity for p-type catalysts, and a smaller increase with the pure oxide, both reversed by methanol removal. The effect of grain size on the rate of conductivity change was also examined and the nature of the changes discussed with regard to electron transfer/ permanent changes in the catalyst and the relative importance of surface/bulk conductivities. The use of Mg-doped ferric oxide catalysts for N 2O decomposition and for the conversion of methanol to formaldehyde is reported in Part II.