Decay Of Electrical Conductivity Research Articles

Technical note: Two-component electrical-conductivity-based hydrograph separation employing an exponential mixing model (EXPECT) provides reliable high-temporal-resolution young water fraction estimates in three small Swiss catchments

Abstract. The young water fraction represents the portion of water molecules in a stream that have entered the catchment relatively recently, typically within 2–3 months. It can be reliably estimated in spatially heterogeneous and nonstationary catchments from the amplitude ratio of seasonal isotope (δ18O or δ2H) cycles of stream water and precipitation, respectively. Past studies have found that young water fractions increase with discharge (Q), thus reflecting the higher direct runoff under wetter catchment conditions. The rate of increase in the young water fraction with increasing Q, defined as the discharge sensitivity of the young water fraction (Sd*), can be useful for describing and comparing catchments' hydrological behaviour. However, the existing method for estimating Sd*, which only uses biweekly isotope data, can return highly uncertain and unreliable Sd* when stream water isotope data are sparse and do not capture the entire flow regime. Indeed, the information provided by isotope data depends on when the respective sample was taken. Accordingly, the low sampling frequency results in information gaps that could potentially be filled by using additional tracers sampled at a higher temporal resolution. By utilizing high-temporal-resolution and cost-effective electrical conductivity (EC) measurements, along with information obtainable from seasonal isotope cycles in stream water and precipitation, we develop a new method that can estimate the young water fraction at the same resolution as EC and Q measurements. These high-resolution estimates allow for improvements in the estimates of the Sd*. Our so-called EXPECT (Electrical-Conductivity-based hydrograph separaTion employing an EXPonential mixing model) method is built upon the following three key assumptions: We construct a mixing relationship consisting of an exponential decay of stream water EC with increasing young water fraction. This has been obtained based on the relationship between flow-specific young water fractions and EC. We assume that the two-component EC-based hydrograph separation technique, using the above-mentioned exponential mixing model, can be used for a time-source partitioning of stream water into young (transit times < 2–3 months) and old (transit times > 2–3 months) water. We assume that the EC value of the young water endmember (ECyw) is lower than that of the old water endmember (ECow). Selecting reliable values from measurements of ECyw and ECow to perform this unconventional EC-based hydrograph separation is challenging, but the combination of information derived from the two tracers allows for the estimation of endmembers' values. The two endmembers have been calibrated by constraining the unweighted and flow-weighted average young water fractions obtained with the EC-based hydrograph separation to be equal to the corresponding quantities derived from the seasonal isotope cycles. We test the EXPECT method in three small experimental catchments in the Swiss Alptal Valley using two different temporal resolutions of Q and EC data: sampling resolution (i.e. we only consider Q and EC measurements during dates of isotope sampling) and daily resolution. The EXPECT method has provided reliable young water fraction estimates at both temporal resolutions, from which a more accurate discharge sensitivity of the young water fraction (SdEXP) could be determined compared with the existing approach. Also, the method provided new information on ECyw and ECow, yielding calibrated values that fall outside the range of measured EC values. This suggests that stream water is always a mixture of young and old water, even under very high or very low wetness conditions. The calibrated endmembers revealed a good agreement with both endmembers obtained from an independent method and EC measurements from groundwater wells. For proper use of the EXPECT method, we have highlighted the limitations of EC as a tracer, identified certain catchment characteristics that may constrain the reliability of the current method and provided recommendations about its adaptation for future applications in catchments other than those investigated in this study.

Decay of electrical conductivity in p-toluene sulfonate doped polypyrrole films

Long term performance of conductivity of p-toluene sulfonic acid (pTSA) doped electrochemically synthesized polypyrrole (PPy) films was estimated from accelerated aging studies between 80 °C and 120 °C. Conductivity decay experiments indicated that overall aging behavior of PPy films deviated from first order kinetics at prolonged aging times at elevated temperatures. However, an approximate value for the activation energy of the conductivity decay of PPy was calculated as E=47.4 kJ/mol, enabling an estimate of a rate constant of k=8.35×10−6/min at 20 °C. The rate of decrease of conductivity was not only temperature dependent but also influenced by the dopant concentration. A concentration of 0.005 M pTSA in the electrolyte resulted in a conductive film and when this film was exposed to 120 °C for a period of 40 h, the conductivity decayed to about 1/20 of its original value. The concentration of pTSA was increased to 0.05 mol/l and when the resulting film was aged in the same way, it showed a decrease in the conductivity to about 1/3 of its original value. Both microwave transmission and dc conductivity data revealed that highly doped films were considerably more electrically stable than lightly doped films. The dopant had a preserving effect on the electrical properties of PPy.

Diffusion of O2 in C60 crystal by measuring the decay of electrical conductivity

The time dependence of the decay of dark electrical conductivity σ(t) from C60 crystals under air exposure was investigated at different temperatures. The decay of σ(t) can be fitted via a stretched exponential function, indicating that the diffusion of O2 in C60 crystal follows a hierarchically constrained dynamic. The diffusivity of molecular oxygen in C60 crystal is estimated using the least-square fitted time constant, and an activation energy EA=1.5eV corresponding to the diffusion process is deduced from the Arrhenius plot. The mechanism of the diffusion process is then discussed.

Thermal degradation of polypyrrole: effect of temperature and film thickness

Thermal degradation of a series of polypyrrole films doped with p-toluene sulfonate has been investigated by examining the effect of film thickness (12–68 μm) and temperature (70–150 °C) on the rate of decay of electrical conductivity. The kinetics are complex: for thin films and thick films at higher temperatures, the decay is proportional to t 1 2 and a similarity to diffusion kinetics is noted; at low temperatures the conductivity decay of thicker films follows first-order kinetics for at least 100 h. It is suggested that the decay is explained by oxidation and that either chemical reaction or oxygen diffusion will be rate determining, depending on the film thickness and ageing temperature. At higher temperatures, the deduced diffusion coefficient D was independent of film thickness. The Arrhenius plot of D or of the time-temperature shift factor a T showed a change of slope at 90 °C, suggesting the possibility of a glass transition temperature in the film.

Investigation of the electrical conductivity of polystyrene under irradiation

A kinetic study has been made of the attainment and decay of electrical conductivity induced in polystyrene irradiated with accelerated electron pulses. The behaviour of the rapid and slow constituents of the delayed component has been investigated, whilst varying the electric field. The effect of the irradiation dose on electrical conductivity induced in strong electric fields (⩾ 5 × 10 5 V/cm) has been ascertained. The computer calculations show that the rapid constituent of a delayed component with a hyperbolic decay constant of 0.2 μsec may be accounted for satisfactorily in the framework of the Rouse-Fowler model, provided that the traps are small enough (liberation times not exceeding 100 nsec).

On the reversible change in the electrical conductivity of a polyimide during pulsed irradiation

A kinetic study has been made of the attainment and decay of electrical conductivity excited in a polyimide irradiated with fast electron pulses (particle energy 8 MeV, 40 nsec and 2 μsec pulses). It has been found that the delayed component of the radiation induced electrical conductivity consists of fast (τ 1 2 =150 nsec) and slow (τ 1 2 =2 μ sec) components. It is proposed that the fast component is related to a rearrangement of captured charges from shallow to deeper traps, while the slow component is responsible for the experimentally observed inhomogeneous character of the recombination of charge carriers created in the polyimide by irradiation. It is shown that relaxation of induced electrical conductivity after the cessation of irradiation is not a function of the electric field voltage. An estimate of the captured charge drift mobility at room temperature gives μ dr=3·6×10 −7 cm 2/W·sec.

Experiments on radiating xenon plasma flows in an arc driven shock tube

The electrical conductivity of xenon plasma in an arc driven shock tube was measured by means of a conductivity probe of magnetic induction type. The decay of continuous emission intensities was also measured at the two wavelengths 4425 Å and 3975Å. The initial xenon pressure (P1) ranged from 1.5 to 10 torr. The shock Mach number (Ms) ranged roughly from 15 to 24. The effect of radiation cooling on the decay of electrical conductivity and that of continuous emission intensity was studied together with our previous measurements in a pressure driven shock tube, (P1= 1-5 torr and Ms = 9-14).For higher. shock Mach numbers, the measured decrease of electrical conductivity and that of continuous emission intensity. could be correlated with continuum radiation loss. For lower shock Mach numbers at P1=1 and 2 torr, however, the decrease is much faster than the calculated value assuming continuum radiation loss alone. To obtain a possible explanation. for this discrepancy, the influence of line radiation loss was briefly discussed.