Effect of manganese and cobalt doping on conductivity of ZnO based varistors: a study by complex plane modulus

Effect of manganese and cobalt doping (0.50 mole%) on electrical properties of ZnO based varistors has been studied using complex plane modulus analysis. It is found that total resistivity of Mn doped sample is more as compared to that of Co doped sample. This has been ascribed to existence of Mn in variable valence states viz. Mn²⁺, Mn³⁺ and Mn⁴⁺ which promotes hopping conduction leading to increase in the conductivity as compared to Co doped sample, in which Co exists predominantly in +3 state with traces of Co²⁺ or Co⁺⁴ states. This accounts for its less conductivity. Mechanism of conduction is the same for grains and grainboundaries.     

Well Loss Estimation: Variable Pumping Replacing Step Drawdown Test

An optimization method is presented for simultaneous estimation of aquifer parameters and well loss parameters utilizing all the drawdowns observed during a variable rate pumping or multiple step pumping test. The proposed method does not require any graphical analysis. It is shown that a variable rate pumping test is a better substitute for the conventional step drawdown test to estimate well loss parameters. It suggests that the pumping rate may be changed frequently without waiting for a near steady state to be reached (or a selected duration, say 60 min) in each step of a conventional step drawdown test. This can result in a substantial saving of time and money involved in conducting a step drawdown test with a view to estimate well loss parameters. This gives a greater number of distinct discharges, which improves the estimates of the well loss parameters. Application of the method is demonstrated on published data sets, the results of which show that the parameters estimated using the new method are more reliable as compared to those obtained using prior methods.     

Theory of optical nutation in direct-gap semiconductors due toultrashort resonant laser irradiation

An analytical investigation of optical nutation in direct-gap semiconductors such as GaAs, InSb, and Hg_1-xCd_xTe based on the time-dependent perturbation technique is discussed. The crystals are considered to be irradiated by short pulsed moderate power near-resonant lasers producing significant density of optically-induced free electron-hole pairs. Incoherent dephasing mechanisms have been introduced phenomenologically into the coherent radiation-semiconductor interaction model. The theory, on application to the case of a specific crystal such as Hg_1-xCd_xTe with x=0.18 irradiated by a pulsed 10.6 μm CO₂ laser, manifests distinctly the occurrence of ringing behavior in the transmitted intensity, transient dispersion, and absorption even in the absence of any theoretical averaging or the consideration of the effective density of states     

Temperature behavior and compensation of light-emitting diode

This letter offers a fresh insight into the behavior of light-emitting diode (LED) over temperature. Theoretically and by measurement, it has been shown that equi-intensity curves in the diodes current-voltage plane are nearly a straight line over a very wide range of temperatures. Based on this property, bias voltage and resistance value of a bias circuit have been realized and practical measurement shows the peak-to-peak light intensity variation decreases from 99 % (in case of fixed current bias) to 6 % over the temperature range of -20 C to +80 C for the LED IN6092. This circuit uses no separate temperature sensor or compensating mechanism, but responds directly to the junction temperature of the diodes. This prevents any error caused by temperature gradient, or by self-heating due to power dissipation in the diode.     

Enhanced β-galactosidase production by supplementing whey with cauliflower waste

Among the five Kluyveromyces marxianus strains tested for β-galactosidase production, K. marxianus NCIM 3465 showed maximum enzyme activity of 1.62 IU mg⁻¹ dry weight. Different levels (5–25%, w/v) of dried cauliflower waste were incorporated into whey to evaluate the effect of its supplementation on enzyme production. Although a marginal increase in enzyme production was seen by incorporating 5% and 10% cauliflower waste in whey, nearly 15% increase in β-galactosidase production was observed when cauliflower waste level was increased to 20% compared with whey alone. Supplementing whey with 20% cauliflower waste also decreased the production time. Lactose concentration in whey, mainly responsible for increasing the biological oxygen demand load of the effluent water, decreased from 4.2% to nearly 0% at 24 h. Thus, this study demonstrated that both these by-products/residues could be effectively used for β-galactosidase production at commercial scale.     

Positron emission tomography. Tracing how and why it is sosuccessful

PET is one of the most advanced medical imaging systems widely applied to medical research and clinical use. The present PET scanning technique cannot be performed in small animals such as mice. The detector is not optimal with respect to radiotracer sensitivity due to the lack of spatial resolution. (The problem is further exacerbated due to the lack of a computer model and the unknown amount of radiotracers to be administered for viable detection in small animals.) Thus, the authors are working on a feasibility study to show whether present PET scanning systems can be modified to identify active tumor foci in an orthotopic mouse model of human pancreatic cancer. This way the efficacy of selected standard chemotherapy drugs and novel biological agents can be tested. Ultimately, the goal is the development of novel therapeutic agents against human pancreatic cancer