[en] Chilika Lake is the largest coastal lagoon in Asia and the second largest in the world covering an area of 1100 km² and spread over three districts of Odisha state of India. It is the first Indian wetland designated as a wetland of international importance under the Ramsar Convention in 1981. The lake ecosystem sustains large and diversified resources of plants and animals including fisheries. Pollution of the ecosystem caused by residues of pesticides originating from different sources was assessed through multiple sampling from 2012 to 2016 from three potential sites of contamination, viz., Palur Bridge, Daya River Estuary, and Makara River. Incidence of organochlorinated (OC) pesticide residues was noticed in about 25% water samples. HCH (α, γ&δ), DDD (op ), DDE (op &pp. ) and heptachlor were the OCs detected in concentration varying from 0.025 to 23.4 μg/l. None of the eight targeted synthetic pyrethroid (SP) pesticides was found in water, but among the organophosphates (OP), chlorpyrifos (0.019–2.73 μg/l), and dichlorvos (0.647 μg/l) were recorded. In sediment samples, residues of OC or OP pesticides were not present, but one SP pesticide was recorded. Fish samples were contaminated to the extent of 55%, mostly with residues of OCs and OPs and less with SPs. However, their concentrations were below the permissible limit, so there was no direct threat of health hazards to humans.

[en] Polycrystalline, lead free ceramic, 0.2(K_0.5Bi_0.5TiO₃)–0.8(NaNbO₃) is prepared by high temperature mixed oxide method. Experimental studies reveal the structural and vibrational and ferroelectric properties of the ceramic. The micro structural study exhibits that small grains are distributed uniformly throughout the surface with well-defined grain boundaries and few pores. The structural analysis illustrates that the compound is formed exhibiting the structure as orthorhombic at room temperature with space group Pmc2₁. While adding the NaNbO₃(NN) on K_0.5Bi_0.5TiO₃ (KBT), the vibrational phonon modes undergoes a notable change, as envisaged from the FTIR spectra. From the diffuse absorbance spectra, the optical band gap is found as 3.14 eV and useful for photo catalytic application. Raman spectra exhibit different vibrational modes in the frequency ranging from 130 to 900 cm⁻¹. Polarization study confirms the presence of ferroelectricity. Dielectric analysis infers that phase transition temperature from ferroelectric to paraelectric is observed around 500 °C. The electrical parameters related to microstructure are reflected from impedance analysis. The frequency dependent ac conductivity depends upon frequency validating Jonscher’s power law. While increasing temperature, ac conductivity increases which represents the semiconducting nature of the sample. The bulk conductivity is found to be driven by thermally activated process following Arrhenius relation.

[en] Laser pulse shaping is one of the key elements to generate low emittance electron beams with RF photoinjectors. Ultimately high performance can be achieved with ellipsoidal laser pulses, but 3-dimensional shaping is challenging. High beam quality can also be reached by simple transverse pulse shaping, which has demonstrated improved beam emittance compared to a transversely uniform laser in the ‘pancake’ photoemission regime. In this contribution we present the truncation of a Gaussian laser at a radius of approximately one sigma in the intermediate (electron bunch length directly after emission about the same as radius) photoemission regime with high acceleration gradients (up to 60 MV/m). This type of electron bunch is used e.g. at the European XFEL and FLASH free electron lasers at DESY, Hamburg site and is being investigated in detail at the Photoinjector Test facility at DESY in Zeuthen (PITZ). Here we present ray-tracing simulations and experimental data of a laser beamline upgrade enabling variable transverse truncation. Initial projected emittance measurements taken with help of this setup are shown, as well as supporting beam dynamics simulations. Additional simulations show the potential for substantial reduction of slice emittance at PITZ. (paper)

[en] A new polycrystalline lead-free 0.05(K_0.5Bi_0.5TiO₃)–0.95(NaNbO₃) (KBT–NN) composites ceramics have been prepared by solid-state reaction method and their structural, optical, dielectric, ferroelectric and impedance properties are investigated. X-ray diffraction and Rietveld refinement data reveal that this composites ceramics possesses a perovskite-type orthorhombic structure after the diffusion of K_0.5Bi_0.5TiO₃ into the NaNbO₃. An appreciable change in its vibrational phonon modes of KBT on addition of NaNbO₃ is exhibited in the material as observed from Fourier-transform infrared spectroscopy (FT-IR) spectrum. The optical band gap energy of the sample is determined from the diffused absorbance spectra to be 3.2 eV, which may be useful in photo-catalytic application. In the frequency range of 130–900 cm⁻¹, different vibrational modes are observed from Raman spectrum. Field emission scanning electron microscopy (FE-SEM) images reveal a well-defined and homogeneous morphology. Polarization vs. electric field study confirms the ferroelectricity. Dielectric and complex impedance spectroscopic studies are performed over a wide range of frequency (i.e., 10³–10⁶ Hz) and temperature (30°–500 °C) and it is found that Jonscher’s power law is well applicable to the alternating current (ac) conductivity spectrum. The direct current (dc) conductivity of the material, which depends upon temperature, exhibits the decrease resistance with increase of temperature similar to that of semiconductors. The dc conductivity confirms that the conduction mechanism is influenced by oxygen vacancies.

[en] We report the synthesis and promising electrical properties of a new lead-free ferroelectric ceramic K_0.5Bi_0.5TiO₃-NaNbO₃ (KBT-NN), which can be a candidate of choice for future sensors, FeRAM etc. Mixed-oxide method has been employed to prepare the compound comprising of uniformly distributed grains. Detailed structural analysis revealed its orthorhombic structure with space group Pmc2₁. In-depth analysis of the electrical characterization data revealed a band-gap of 3.11 eV and presence of defects in the bands. Further, ferroelectric phase transition is observed to occur at 395 °C. The dielectric properties of the material, investigated over a wide range of frequencies and temperatures, indicate that its ac conductivity depends upon frequency according to Jonscher’s power law.