Gene expression programming-fuzzy logic method for crop type classification

Crop type classification using remote sensing data plays a vital role in planning cultivation activities and for optimal usage of the available fertile land. Thus a reliable and precise classification of agricultural crops can help improve agricultural productivity. Hence in this paper a gene expression programming based fuzzy logic approach for multiclass crop classification using Multispectral satellite image is proposed. The purpose of this work is to utilize the optimization capabilities of GEP for tuning the fuzzy membership functions. The capabilities of GEP as a classifier is also studied. The proposed method is compared to Bayesian and Maximum likelihood classifier in terms of performance evaluation. From the results we can conclude that the proposed method is effective for classification.

Origin of enhanced photocatalytic activity and photoconduction in high aspect ratio ZnO nanorods

Faceted ZnO nanorods with different aspect ratios were synthesized by a solvothermal method by tuning the reaction time. Increased reaction leads to the formation of high aspect ratio ZnO nanorods largely bound by the prism planes. The high aspect ratio rods showed significantly higher visible light photocatalytic activity when compared to the lower aspect ratio structures. It is proposed that the higher activity is due to better charge separation in the elongated 1D structure. In addition, the fraction of unsaturated Zn2+ sites is higher on the {10 (1) over bar0} facets, leading to better adsorption of oxygen-containing species. These species enhance the production of reactive radicals that are responsible for photodegradation. The photocurrent for these ZnO nanostructures under solar light was measured and a direct correlation between photocurrent and aspect ratio was observed. Since the underlying mechanisms for photodegradation and photocurrent generation are directly related to the efficiency of electron-hole creation and separation, this observation corroborates that the charge separation processes are indeed enhanced in the high aspect ratio structures. The efficiency of photoconduction (electron-hole pair separation) could be further improved by attaching Au nanoparticles on ZnO, which can act as a sink for the electrons. This heterostructure exhibits a high chemisorption of oxygen, which facilitates the production of highly reactive radicals contributing to the high photoreactivity. The suggested mechanisms are applicable to other n-type semiconductor nanostructures with important implications for applications relating to energy and the environment.

Analysis of Bandwidth-Unit-Vector-Distortion Tradeoff in PLL During Abnormal Grid Conditions

Phase-locked loops (PLLs) are necessary in applications which require grid synchronization. Presence of unbalance or harmonics in the grid voltage creates errors in the estimated frequency and angle of a PLL. The error in estimated angle has the effect of distorting the unit vectors generated by the PLL. In this paper, analytical expressions are derived which determine the error in the phase angle estimated by a PLL when there is unbalance and harmonics in the grid voltage. By using the derived expressions, the total harmonic distortion (THD) and the fundamental phase error of the unit vectors can be determined for a given PLL topology and a given level of unbalance and distortion in the grid voltage. The accuracy of the results obtained from the analytical expressions is validated with the simulation and experimental results for synchronous reference frame PLL (SRF-PLL). Based on these expressions, a new tuning method for the SRF-PLL is proposed which quantifies the tradeoff between the unit vector THD and the bandwidth of the SRF-PLL. Using this method, the exact value of the bandwidth of the SRF-PLL can be obtained for a given worst case grid voltage unbalance and distortion to have an acceptable level of unit vector THD. The tuning method for SRF-PLL is also validated experimentally.

Fermions in synthetic non-Abelian gauge potentials: rashbon condensates to novel Hamiltonians

Recent advances in the generation of synthetic gauge fields in cold atomic systems have stimulated interest in the physics of interacting bosons and fermions in them. In this paper, we discuss interacting two-component fermionic systems in uniform non-Abelian gauge fields that produce a spin-orbit interaction and uniform spin potentials. Two classes of gauge fields discussed include those that produce a Rashba spin-orbit interaction and the type of gauge fields (SM gauge fields) obtained in experiments by the Shanxi and MIT groups. For high symmetry Rashba gauge fields, a two-particle bound state exists even for a vanishingly small attractive interaction described by a scattering length. Upon increasing the strength of a Rashba gauge field, a finite density of weakly interacting fermions undergoes a crossover from a BCS like ground state to a BEC state of a new kind of boson called the rashbon whose properties are determined solely by the gauge field and not by the interaction between the fermions. The rashbon Bose-Einstein condensate (RBEC) is a quite intriguing state with the rashbon-rashbon interactions being independent of the fermion-fermion interactions (scattering length). Furthermore, we show that the RBEC has a transition temperature of the order of the Fermi temperature, suggesting routes to enhance the transition temperatures of weakly interacting superfluids by tuning the spin-orbit coupling. For the SM gauge fields, we show that in a regime of parameters, a pair of particles with finite centre-of-mass momentum is the most strongly bound. In other regimes of centre-of-mass momenta, there is no two-body bound state, but a resonance like feature appears in the scattering continuum. In the many-body setting, this results in flow enhanced pairing. Also, strongly interacting normal states utilizing the scattering resonance can be created opening the possibility of studying properties of helical Fermi liquids. This paper contains a general discussion of the physics of Feshbach resonance in a non-Abelian gauge field, where several novel features such as centre-of-mass-momentum-dependent effective interactions are shown. It is also shown that a uniform non-Abelian gauge field in conjunction with a spatial potential can be used to generate novel Hamiltonians; we discuss an explicit example of the generation of a monopole Hamiltonian.

On the mechanism of metal nanoparticle synthesis in the brust-schiffrin method

Brust-Schiffrin synthesis (BSS) of metal nanoparticles has emerged as a major breakthrough in the field for its ability to produce highly stable thiol functionalized nanoparticles. In this work, we use a detailed population balance model to conclude that particle formation in BSS is controlled by a new synthesis route: continuous nucleation, growth, and capping of particles throughout the synthesis process. The new mechanism, quite different from the others known in the literature (classical LaMer mechanism, sequential nucleation-growth-capping, and thermodynamic mechanism), successfully explains key features of BSS, including size tuning by varying the amount of capping agent instead of the widely used approach of varying the amount of reducing agent. The new mechanism captures a large body of experimental observations quantitatively, including size tuning and only a marginal effect of the parameters otherwise known to affect particle synthesis sensitively. The new mechanism predicts that, in a constant synthesis environment, continuous nucleation-growth-capping mechanism leads to complete capping of particles (no more growth) at the same size, while the new ones are born continuously, in principle leading to synthesis of more monodisperse particles. This prediction is validated through new experimental measurements.

Aluminium coated carbon nanotube film for wavelength-selective surface

We report selective optical reflectance in an aluminium (Al) coated flexible carbon nanotube (CNT) thin film over a wide range of wavelengths (500-2500 nm). Selective-wavelength surface is achieved by coating CNT surfaces with Al thin film that presented a maximum optical reflectivity of similar to 65% in the infrared region. However, CNT film alone showed a reflectance of 15-20% over a larger range of wavelengths without any structural modification, which has not been realized so far. Moreover, a tailorable reflectance in CNT is shown to be achieved by tuning various parameters, namely, the porosity of the material, angle of an incident light, and refractive index of the materials. Owing to higher infrared reflectivity and thermal diffusivity, Al coated CNT presents a potential for a high efficiency solar collector. (C) 2013 AIP Publishing LLC.

Evolution of ferromagnetism from a frustrated state in LixNi(2-x)O2 (0.67 < x < 0.98)

Two-dimensional triangular-lattice antiferromagnetic systems continue to be an interesting area in condensed matter physics and LiNiO2 is one such among them. Here we present a detailed experimental magnetic study of the quasi-stoichiometric LixNi2-xO2 system (0.67tuning the Li deficiency in a controlled manner, an increase in the ordering temperature is observed. Most strikingly, with the Li deficiency the nature of the magnetic ground state is changed from spin glass to ferromagnetic, with two intermediate states-namely cluster glass and re-entrant spin glass. The critical behaviour of the re-entrant spin glass is also studied here. The critical exponents (beta, gamma and delta) are extracted from the modified Arrot plot, Kouvel-Fisher method, and critical isotherm analysis. The critical exponents match with the long-range mean-field model. The values of the critical exponents are confirmed by the Widom scaling law: delta = 1 + gamma beta(-1). Furthermore, the universality class of the scaling relations is verified, where the scaled m and scaled h collapse into two branches. Finally, based on our observations, a phase diagram is constructed.

The effect of Se doping on spectroscopic and electrical properties of GeTe

Selenium doped thin films of GeTe alloys were investigated for their structural modifications by X-ray Diffraction, Fourier Transform Infrared Spectroscopy, X-ray photoelectron Spectroscopy (XPS) and Raman Spectroscopy. The band gap increase from 0.69 to 1.10 eV with increasing Se addition signifies the possibility of band gap tuning in the material. Disorder decreases, band widens and conductivity saturates about 0.20 at.% of Se addition. Structural changes are explained by the bond theory of solids. The as-deposited films are amorphous and 0.50 at.% Se alloy forms a homogeneous amorphous phase with a mixture of Ge-Se and Te-Se bonds. The XPS core level spectra and Raman spectra investigation clearly indicate the formation of Ge-Se, GeTe2 and Te-Se bonds with Se addition. Crystallization temperature is found to be increasing with Se and the 0.10 at.% Se alloy is found to have a higher resistance contrast compared to other Se concentration alloys. Up to 0.10 at.% of Se addition can enhance GeTe phase change memory properties. (C) 2013 Elsevier B.V. All rights reserved.

Origin of enhanced thermoelectric properties of doped CrSi2

Using first principles density functional theory, we report for CrSi2, a linear relationship between thermodynamic charge state transition levels of defects and maxima of thermopower T-m, thus proposing a unique way of tuning thermoelectric properties. We show for doped CrSi2 that the peak of thermopower occurs at the temperature which corresponds to the position of the defect transition level. Therefore, by modifying the defect transition level, a thermoelectric material with a given operational temperature can be designed.

A rain forest dusk chorus: cacophony or sounds of silence?

A rain forest dusk chorus consists of a large number of individuals of acoustically communicating species signaling at the same time. How different species achieve effective intra-specific communication in this complex and noisy acoustic environment is not well understood. In this study we examined acoustic masking interference in an assemblage of rain forest crickets and katydids. We used signal structures and spacing of signalers to estimate temporal, spectral and active space overlap between species. We then examined these overlaps for evidence of strategies of masking avoidance in the assemblage: we asked whether species whose signals have high temporal or spectral overlap avoid calling together. Whereas we found evidence that species with high temporal overlap may avoid calling together, there was no relation between spectral overlap and calling activity. There was also no correlation between the spectral and temporal overlaps of the signals of different species. In addition, we found little evidence that species calling in the understorey actively use spacing to minimize acoustic overlap. Increasing call intensity and tuning receivers however emerged as powerful strategies to minimize acoustic overlap. Effective acoustic overlaps were on average close to zero for most individuals in natural, multispecies choruses, even in the absence of behavioral avoidance mechanisms such as inhibition of calling or active spacing. Thus, call temporal structure, intensity and frequency together provide sufficient parameter space for several species to call together yet communicate effectively with little interference in the apparent cacophony of a rain forest dusk chorus.

Physics and chemistry of CdTe/CdS thin film heterojunction photovoltaic devices: fundamental and critical aspects

Among the armoury of photovoltaic materials, thin film heterojunction photovoltaics continue to be a promising candidate for solar energy conversion delivering a vast scope in terms of device design and fabrication. Their production does not require expensive semiconductor substrates and high temperature device processing, which allows reduced cost per unit area while maintaining reasonable efficiency. In this regard, superstrate CdTe/CdS solar cells are extensively investigated because of their suitable bandgap alignments, cost effective methods of production at large scales and stability against proton/electron irradiation. The conversion efficiencies in the range of 6-20% are achieved by structuring the device by varying the absorber/window layer thickness, junction activation/annealing steps, with more suitable front/back contacts, preparation techniques, doping with foreign ions, etc. This review focuses on fundamental and critical aspects like: (a) choice of CdS window layer and CdTe absorber layer; (b) drawbacks associated with the device including environmental problems, optical absorption losses and back contact barriers; (c) structural dynamics at CdS-CdTe interface; (d) influence of junction activation process by CdCl2 or HCF2Cl treatment; (e) interface and grain boundary passivation effects; (f) device degradation due to impurity diffusion and stress; (g) fabrication with suitable front and back contacts; (h) chemical processes occurring at various interfaces; (i) strategies and modifications developed to improve their efficiency. The complexity involved in understanding the multiple aspects of tuning the solar cell efficiency is reviewed in detail by considering the individual contribution from each component of the device. It is expected that this review article will enrich the materials aspects of CdTe/CdS devices for solar energy conversion and stimulate further innovative research interest on this intriguing topic.

Integrated relative translation and rotation control of spacecraft formations

Formation flying of small spacecraft provides a way to improve the resolution by aperture distribution. This requires autonomous control of relative position and relative attitude. The present work addresses the formation control using a PID controller to maintain both relative position and relative attitude. To avoid continuous pulsing due to noise, a dead-band has been provided in the position loop. PID control has been selected to maintain the formation in the presence of unmodeled disturbances. Simulations show that the proposed controller meets the required translational and rotational relative motions even in the presence of disturbances.

State estimation of spiralling target using UKF with generalized sinusoidal target acceleration model

Hit-to-kill interception of high velocity spiraling target requires accurate state estimation of relative kinematic parameters describing spiralling motion. In this pa- per, spiraling target motion is captured by representing target acceleration through sinusoidal function in inertial frame. A nine state unscented Kalman filter (UKF) formulation is presented here with three relative positions, three relative velocities, spiraling frequency of target, inverse of ballistic coefficient and maneuvering coef-ficient. A key advantage of the target model presented here is that it is of generic nature and can capture spiraling as well as pure ballistic motions without any change of tuning parameters. Extensive Six-DOF simulation experiments, which includes a modified PN guidance and dynamic inversion based autopilot, show that near Hit-to-Kill performance can be obtained with noisy RF seeker measurements of gimbal angles, gimbal angle rates, range and range rate.

Triarylborane conjugated acacH ligands and their BF2 complexes: facile synthesis and intriguing optical properties

A facile synthetic route for a new class of organoborane compounds (Mes)(2)B-arene-acacH and (Mes)(2)Barene-acacBF2 (Mes = mesityl and arene = C6H4 or C6Me4) is reported. The new dyads exhibit intriguing photophysical properties. A small structural change in spacer connecting the two chromophores leads to fine tuning of photophysical properties. The dyad containing 2,3,5,6-tetramethyl phenyl spacer acts as a selective ``turn-on'' chemodosimetric sensor for cyanide ion. Steric crowding around the boron centre significantly alters anion binding events. From NMR titration studies it is established that fluoride and cyanide follow different binding mechanisms which lead to intriguing optical properties in the reported probes.

Solvent polarity and nanoscale morphology in bulk heterojunction organic solar cells: A case study

Organic bulk heterojunction solar cells were fabricated under identical experimental conditions, except by varying the solvent polarity used for spin coating the active layer components and their performance was evaluated systematically. Results showed that presence of nitrobenzene-chlorobenzene composition governs the morphology of active layer formed, which is due to the tuning of solvent polarity as well as the resulting solubility of the P3HT:PCBM blend. Trace amount of nitrobenzene favoured the formation of better organised P3HT domains, as evident from conductive AFM, tapping mode AFM and surface, and cross-sectional SEM analysis. The higher interfacial surface area thus generated produced cells with high efficiency. But, an increase in the nitrobenzene composition leads to a decrease in cell performance, which is due to the formation of an active layer with larger size polymer domain networks with poor charge separation possibility. (C) 2014 AIP Publishing LLC.