Estimation of distribution coefficient of polonium in geological matrices around uranium mining site

In case of ground (groundwater) contamination or contaminants release from the disposal modules (facilities) to the geo-environment, the fate of contaminant transport is mainly governed by the parameter called distribution (partition) coefficient, K _d. It is a measure of sorption of contaminants to soils. For that the sorption of polonium in soil were carried out using laboratory batch method in different soil samples collected from different places around Turamdih uranium mining site. The kinetics of polonium sorption were also carried out at different time intervals which clearly indicates that sorption equilibrium for polonium achieved at around 72 h. The K _d for polonium varies from 1,443 to 7,501.3 L/kg in soil samples. Chemical characterization of soil and ground water samples were carried out to know the effect of various chemical parameters with distribution coefficient of polonium.     

Single-particle and collective excitations in quantum wires made up of vertically stacked quantum dots: zero magnetic field

We report on the theoretical investigation of the elementary electronic excitations in a quantum wire made up of vertically stacked self-assembled InAs/GaAs quantum dots. The length scales (of a few nanometers) involved in the experimental setups prompt us to consider an infinitely periodic system of two-dimensionally confined (InAs) quantum dot layers separated by GaAs spacers. The resultant quantum wire is characterized by a two-dimensional harmonic confining potential in the x-y plane and a periodic (Kronig-Penney) potential along the z (or the growth) direction within the tight-binding approximation. Since the wells and barriers are formed from two different materials, we employ the Bastard's boundary conditions in order to determine the eigenfunctions along the z direction. These wave functions are then used to generate the Wannier functions, which, in turn, constitute the legitimate Bloch functions that govern the electron dynamics along the direction of periodicity. Thus, the Bloch functions and the Hermite functions together characterize the whole system. We then make use of the Bohm-Pines' (full) random-phase approximation in order to derive a general nonlocal, dynamic dielectric function. Thus, developed theoretical framework is then specified to work within a (lowest miniband and) two-subband model that enables us to scrutinize the single-particle as well as collective responses of the system. We compute and discuss the behavior of the eigenfunctions, band-widths, density of states, Fermi energy, single-particle and collective excitations, and finally size up the importance of studying the inverse dielectric function in relation with the quantum transport phenomena. It is remarkable to notice how the variation in the barrier- and well-widths can allow us to tailor the excitation spectrum in the desired energy range. Given the advantage of the vertically stacked quantum dots over the planar ones and the foreseen applications in the single-electron devices and in the quantum computation, it is quite interesting and important to explore the electronic, optical, and transport phenomena in such systems.     

A finite element model for nonlinear behaviour of piezoceramics under weak electric fields

It has been experimentally observed that piezoceramic materials exhibit different types of nonlinearities under different combinations of electric and mechanical fields. When excited near resonance in the presence of weak e to a Duffinor such as jump phenomena and presence of superharmonics in the response spectra. There has not been much work in the litrature to model these types of nonlinearities. Some authors have developed one-dimensional models for the above phenomenon and derived closed-form solutions for the displacement response of piezo-actuators. However, the generalized three-dimensional (3-D) formulation of electric enthalpy, the variational formulation and the FEM implementation have not yet been addressed, which are the focus of this paper. In this work, these nonlinearities have been modelled in a 3-D piezoelectric continuum using higher order quadratic and cubic terms in the generalized electric enthalpy density function. The coupled nonlinear finite element equations have been derived using variational formulation. A special linearization technique for assembling the nonlinear matrices and solution of the resulting nonlinear equations has been developed. The method has been used for simulating the nonlinear frequency response of a lead zirconate titanate plate excited near its first in-plane vibration resonance frequency with sinusoidal excitations of different electric field strengths. The results have been compared with those of the experiment.     

2,3-Pyridinediol as a specific reagent for the detection of iron

Summary Iron complexation with 2,3-pyridinediol is used to detect iron specifically in presence of common ions present in the scheme of qualitative analysis. The method finds use in detection of iron in alloys, salts and medicinal preparations.

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Zusammenfassung Die Komplexbildung des Eisens mit 2,3-Pyridindiol wurde für den spezifischen Nachweis dieses Elements in Gegenwart üblicher Ionen im Analysengang verwendet. Dieser Nachweis wurde in Legierungen, in Salzen und in pharmazeutischen Präparaten durchgeführt.

     

Observation of Meyer-Neldel rule in thermally activated Poole-Frenkel photoconduction in a-Se<Subscript>70</Subscript>Te<Subscript>30−<Emphasis Type="Italic">x</Emphasis></Subscript>Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> thin films

In the present paper, we report the compensation effect on photoconductivity of thin films of Se₇₀Te_30−x Cd _x (x = 2, 4, 6) alloys for high field conduction. Steady state photoconductivity measurements have been made in thin films for different electric fields. The photoconduction was found to be ohmic at low fields and Poole-Frenkel type at high fields. Meyer-Neldel rule (MN rule) for the pre-exponential factor (σ _ph)₀ and activation energy (ΔE _ph) of photoconduction in thin films of Se₇₀Te_30−x Cd _x is observed in the present study.     

Structural interpretation of specific heat measurements on glassy Se100− x Sb x alloys

Differential scanning calorimetry was used to study glassy Se_{100- x} Sb _x (x = 2, 4, 6, 8 and 10) alloys at a heating rate of 10°C min^?1 under non-isothermal conditions. An extremely large increase in the specific heat, C_p , was observed at the glass-transition temperature. It was also found that the values of C_p below and above the glass-transition temperature, C_pg and C_pe , respectively, are highly composition dependent. This indicates that the Sb additive used in the present study influences the structure of the a-Se. The variation of C_p reveals local extrema in the Se–Sb glassy system at x = 4 and x = 8. The composition dependence of both C_pe and C_pg is explained in terms of the atomic structure.     

57Fe Mössbauer spectroscopic study of nanostructured zinc ferrite

Nanosize zinc ferrite particles, prepared by nitrate method, were investigated by XRD, TEM, ⁵⁷Fe Mössbauer spectroscopy and VSM. The average particle size in this system varies from 10 to 62 nm as the sintering temperature increases from 300°C to 1,000°C. The lattice parameters in this system are almost constant at a value of ～8.41 Å. The Mössbauer spectra of all the sintered samples show a single doublet. The Mössbauer hyperfine parameters show little change with the change of sintering temperature. The doublets are ascribed to the presence of superparamagnetism in this system, which is also corroborated by the VSM measurements.     

Characterization of the 46.9-nm soft X-ray laser beam from a capillary discharge

Intense lasing had been obtained from argon plasma in the soft X-ray region from a capillary discharge plasma system. Different diagnostics have been used to characterize the lasing properties by recording the temporal, spatial, and spectral profiles of the emission. The divergence measurement indicates that the soft X-ray laser beam has good directionality with a divergence of 3.5 mrad. The spectrum of the laser beam measured using a transmission grating showed intense lasing line at 46.9 nm. Diffraction orders as high as 10th orders were observed. The temporal profile recorded with a vacuum diode showed a distinct laser peak with a pulse width ~1.2 ns (FWHM). In addition, the coherence of the X-ray laser beam was also confirmed from the high-contrast interference fringes (visibility ~85 %) recorded using double slits.     

Growth of Cyanobacteria: Optimization for Increased Carbohydrate Content

Growths of Lyngbya limnetica and Oscillatoria obscura were investigated at varying pH, light intensity, temperature, and trace element concentration with a view to optimize these parameters for obtaining the maximum carbohydrate content. The maximum growth for both strains was obtained at pH 9.0 and temperature 20 ± 3 °C using a light intensity of 68.0 μmol m^?2 s^?1 with continuous shaking. Growth under the nitrogen starvation condition affected the carbohydrate content more compared to the phosphorus starvation, and maximum concentrations were found as 0.660 and 0.621 g/g of dry biomass for L. limnetica and O. obscura, respectively. Under the optimized nitrogen-rich conditions, the specific growth rates for the two strains were found to be 0.187 and 0.215 day^?1, respectively. The two-stage growth studies under nitrogen-rich (stage I) followed by nitrogen starvation (stage II) conditions were performed, and maximum biomass and carbohydrate productivity were found as 0.088 and 0.423 g L^?1 day^?1 for L. limnetica. This is the first ever attempt to evaluate and optimize various parameters affecting the growth of cyanobacterial biomass of L. limnetica and O. obscura as well as their carbohydrate contents.