Magneto-transport properties of Fe-doped LSMO manganites

Magneto-transport measurements have been performed on La_0.67Sr_0.33Mn_1−xFe_xO₃ (x = 0.0, 0.05 and 0.07) manganites synthesized by solid state route. The overall nature of AC susceptibility is found to be frequency independent. With the substitution of Mn by Fe, the transport properties dramatically change suppressing the double-exchange interaction. This in turn weakens the ferromagnetism and consequently decreases the paramagnetic to ferromagnetic transition temperature (T_c). However, DC electrical resistivity of the samples show board hump at metal-insulator transition temperature (T_MI) in contrary with sharp transition at T_c and T_MI < T_c indicating decoupling of electrical and magnetic properties. Resistivity behavior of these samples can be well explained by the consideration of bond percolation model which is basically developed from effective approximation method.     

Kinetics of temperature-dependent photoinduced redox reactions in a photoelectrochemical cell

The effect of temperature on the electrode kinetics of photovoltage generation in photoelectrochemical (PEC) cells consisting of a phenazine dye-EDTA system, separated from an aqueous solution of an electron acceptor like iodine by a salt bridge has been studied. The phenazine dyes used are phenosafranin, safranin-O, and safranin-T. The maximum photovoltages (V_oc) generated and the sunlight engineering efficiency (SEE) have been found to increase with increasing temperature, but there is a fixed critical temperature for each dye above which the V_oc decreases: 29°C for phenosafranin, 35°C for safranin-T, and 40°C for safranin-O. The photovoltage growth and decay follow the functional forms related to the relaxation times. The rate constants for the forward and backward reactions have been calculated from these relaxation times at different temperatures. The rate of the photoinduced chemical reaction increases with an increase in temperature from 20°C–50°C for all the dyes, with concomitant decrease for the backward reaction. The free energies of electron transfer across the electrode/electrolyte interface have been calculated. The activation energies calculated from the rate constants at different temperatures for phenosafranin-EDTA, safranin-T-EDTA, and safranin-O-EDTA reactions are 5.14, 5.60, and 5.63 kJ mol⁻¹ respectively.     

Finite‐time posture stabilization of the unicycle mobile robot using only position information: A discrete‐time sliding mode approach

The posture stabilization of a unicycle mobile robot is useful in executing parking and docking maneuvers. It becomes more advantageous to guarantee the posture stabilization in finite time for a battery operated robot, especially in an application involving multiple robots. This paper addresses the posture stabilization of the unicycle mobile robot in finite time, especially when only the position information is available. We adopt the reaching law approach and design a discrete‐time sliding mode (DSM) controller by finitely discretizing the chained form of the unicycle, using the notion of multirate input sampling. Finite‐time stabilization of the equilibria is achieved by using multirate piecewise continuous inputs. Furthermore, the control inputs are realized using multirate output‐feedback (MROF) technique, wherein the states are estimated using the knowledge of the past fast output samples and immediate past control inputs. The proposed MROF‐DSM strategy avoids undesirable chatter in the system response owing to the nonswitching‐type controller and guarantees the stabilization in finite time. Simulations demonstrate the efficacy of the proposed method.     

Comparison of dc electric field and tapered wiggler free electron laser efficiency enhancement schemes

A constant parameter wiggler free electron laser using a dc electric field for efficiency enhancement is compared to several tapered wiggler efficiency enhancement schemes. Analytical expressions for the efficiency in the plane wave, infinitesimally small radius electron beam limit are derived and compared. Numerical simulations for a Gaussian radiation field and finite radius electron beam with an output radiation wavelength of 2 μm are presented. For finite radius electron beams, the extraction efficiency using a dc electric field is somewhat greater than or equal to that using proposed tapering schemes. While the dc field offers flexibility in efficient, tunable laser design, the required field strengths for visible radiation are in the megavolt/meter range.     

Solar cells consisting of phenazine dyes in polymer matrix

We have constructed p−n heterojunction solar sandwich cells with phenazine dyes in a thin film of polyvinyl alcohol placed between a conducting glass coated with indium oxide and a platinum foil. The current-voltage relations of the cells have been measured in the dark and light under both forward and reverse biases.     

The effect of seasonal variation on automated land cover mapping from multispectral airborne laser scanning data

Multispectral airborne laser scanning (MS-ALS) sensors are a new promising source of data for automated mapping methods. Finding an optimal time for data acquisition is important in all mapping applications based on remotely sensed datasets. In this study, three MS-ALS datasets acquired at different times of the growing season were compared for automated land cover mapping and road detection in a suburban area. In addition, changes in the intensity were studied. An object-based random forest classification was carried out using reference points. The overall accuracy of the land cover classification was 93.9% (May dataset), 96.4% (June) and 95.9% (August). The use of the May dataset acquired under leafless conditions resulted in more complete roads than the other datasets acquired when trees were in leaf. It was concluded that all datasets used in the study are applicable for suburban land cover mapping, however small differences in accuracies between land cover classes exist.