Self-similarity of electrostatic fluctuations in a linear magnetised plasma system

In this Letter the long-range time correlations present in the fluctuation data in presence of electrostatic instability in a magnetised dc discharge plasma is presented. The electrostatic instability is generated due to the effect of crossed electric and magnetic field (E×B flow) and has intermediate frequency ranging from 50 to 100 MHz. Hurst exponent, the self-similarity parameter is calculated with the help of different statistical methods suggested by many researchers to determine the long-range time correlation present in fluctuation dynamics in the plasma column. The fluctuation in the ion saturation current is measured by a Langmuir probe for the study and the measurement is done both radially and axially in the plasma system. Estimated results clearly expose the self-similar character of the fluctuations with self-similarity parameters having values from 0.65 to 0.90 through the presence of long-range time correlation.     

Water wave scattering by two sharp discontinuities in the surface boundary conditions

^** Corresponding author. Email: biren{at}isical.ac.in The problem of water wave scattering by two sharp discontinuitiesin the surface boundary conditions involving infinitely deepwater is examined here by reducing it to two coupled Carleman-typesingular integral equations. The discontinuities arise due tothe presence of two types of non-interacting materials floatingon the surface, one type being in the form of an infinite stripof finite width sandwiched between another type. The non-interactingmaterials form an inertial surface which is a mass-loading modelof floating ice and is regarded as a material of uniform surfacedensity having no elastic property. The two integral equationsare solved approximately by assuming the two discontinuitiesto be widely separated, and approximate analytical expressionsfor the reflection and transmission coefficients are also obtained.This problem has applications in wave propagation through stripsof frazil or pancake ice modelled as floating inertial surfaces.Numerical results for the reflection coefficient are depictedgraphically against the wave number for different values ofthe surface densities of the two types of floating materials.The main feature of the graphs is the oscillatory nature ofthe reflection coefficient and occurrence of zero reflectionfor an increasing sequence of discrete values of the wave number.A direct analytical treatment to solve the integral equationsnumerically, when the separation length between the two discontinuitiesis arbitrary, is also indicated. For the case of more than twodiscontinuities the solution methodology of the correspondingscattering problem is described briefly.     

On the Carey–Helton–Howe–Pincus trace formula

In this article, we give a new proof of the Carey–Helton–Howe–Pincus trace formula using Kato's theory of “relatively-smooth” operators and Krein's trace formula.     

Convergence of linear functions of Pfeifer records

The probabilistic behaviour of partial sums of upper and lower records has been studied in the literature. In this article, we take a broader view and study partial sums of record like sequences. We show that such sequences converge in distribution to normal and lognormal distribution. In particular our results apply to Pfeifer records. We also show the strong convergence of partial sums of lower Pfeifer records under suitable assumptions.     

Ab initio study of K adsorption on a Ag(100) surface

Ab initio Hartree–Fock calculations are reported for the chemisorption of K on Ag using three different types of clusters to model the system. Geometry optimization is done in 4 degrees of freedom. It is found that since there is an absence of complete charge transfer between the adsorbate and substrate, the interaction can be interpreted as being predominately covalent in nature.     

Modulating magnetic anisotropy in Ln(iii) single-ion magnets using an external electric field

Single-molecule magnets have potential uses in several nanotechnology applications, including high-density information storage devices, the realisation of which lies in enhancing the barrier height for magnetisation reversal (U_eff). However, Ln(iii) single-ion magnets (SIMs) that have been reported recently reveal that the maximum value of U_eff values that can be obtained by modulating the ligand fields has already been achieved. Here, we have explored, using a combination of DFT and ab initio CASSCF calculations, a unique way to enhance the magnetisation reversal barrier using an oriented external electric field in three well-known Ln(iii) single-ion magnets: [Dy(Py)₅(O^tBu)₂]⁺ (1), [Er{N(SiMe₃)₂}₃Cl]⁻ (2) and [Dy(Cp^Me3)Cl] (3). Our study reveals that, for apt molecules, if the appropriate direction and values of the electric fields are chosen, the barrier height can be enhanced by twice that of the limit set by the ligand field. The application of an electric field along the equatorial direction was found to be suitable for oblate shaped Dy(iii) complexes and an electric field along the axial direction was found to enhance the barrier height for a prolate Er(iii) complex. For complexes 2 and 3, the external electric field was able to magnify the barrier height to 2–3 times that of the original complexes. However, a moderate enhancement was noticed after application of the external electric field in the case of complex 1. This novel non-chemical fine-tuning approach to modulate magnetic anisotropy is expected to yield a new generation of SIMs.

Using a combination of theoretical tools, we show that the application of an external electric field in a certain direction can boost the axiality beyond that set by the ligands, opening up a new avenue for the generation of novel SIMs.     

ICP-AES analysis of impurities in PuO2 after separation of Pu by TOPO impregnated XAD-4

Nuclear fuels should meet some specified characteristics to achieve their better performance in the reactor. Hence controlling and monitoring of trace level elements in the fuel materials are essential. Atomic emission spectroscopic methods are most popular for the trace level analysis. An ICP-AES procedure is described here for the trace level impurity analysis of PuO₂ produced through PUREX process. To avoid the Pu interference in the impurity analysis, initially the Pu was separated by extraction chromatography using TOPO impregnated XAD-4 resin. Magnitude of Pu interference in the impurities spectra lines was investigated. Moreover the recovery of impurity elements using the resin was established.