Magnetic force microscopic study of the magnetic field induced antiferro to ferrimagnetic transition in Mn1.85Co0.15Sb

Magnetic field induced first order antiferromagnetic (AFM) to ferrimagnetic (FRI) transition in polycrystalline Mn_1.85Co_0.15Sb has been studied using magnetic force microscopy (MFM) at 60 K and up to 8 T magnetic fields. Our MFM studies provide real space visualization of AFM to FRI transition. It shows growth (decay) of FRI phase with increasing (decreasing) magnetic field. The hysteretic behavior and co-existing FRI and AFM phases across the critical field required for FRI-AFM transition in Mn_1.85Co_0.15Sb are highlighted. This study demonstrates the potential of MFM for studying phase co-existence at high field and low temperatures.     

Self-organized transformation to polyaniline nanowires by pulsed energetic electron irradiation in a plasma focus device

An ingenious method for fabricating network of polyaniline nanowires at room temperature in microsecond timescale is demonstrated by using the pulsed electron beam of a plasma focus device. The electron beam of the plasma focus device having a wide range of energies (10-200 keV) was irradiated on to the freestanding polyaniline film. The growth of polyaniline nanowires on the surface of film sample is confirmed by field emission scanning electron microscope images showing nanowires of about 50-80 nm in diameter and up to few tens of micrometers in length.     

Synthesis of nanocrystalline multiphase titanium oxycarbide (TiC<Subscript>x</Subscript>O<Subscript>y</Subscript>) thin films by UNU/ICTP and NX2 plasma focus devices

Nanocrystalline multiphase titanium oxycarbide (TiC_xO_y) thin films composed of TiC₂, TiO_0.325, Ti₂O₃ and graphitic carbon have been deposited on titanium substrates, using energetic carbon ions delivered by the UNU/ICTP and the NX2 plasma focus devices operated at different repetition rates. X-ray diffraction (XRD) patterns of the nanocomposite films reveal the relative transformation of various oxide and carbide phases accompanied by the suppression of the TiC₂ phase when the energy flux of the ion beam and the repetition rate are increased. A field emission scanning electron microscope (FESEM) with an energy dispersive X-ray spectroscopy (EDS) attachment reveals a non-porous microcrack-free nanocrystalline granular surface morphology of the composite films with uniform carbon distribution. X-ray photoelectron spectroscopy (XPS) confirms the formation of oxycarbides (TiC_xO_y) along with significant carbon adsorbate. Raman studies of the films also verify the relative phase transformation in the TiC_xO_y nanocomposite by tuning the deposition parameters. The Vickers microhardness of the sample surface is improved more than 400%. PACS 52.59.Hq; 52.77.Dq; 68.55.Jk; 81.15.-z; 81.65.Lp     

Geometrical characterization techniques for microlens made by thermal reflow of photoresist cylinder

Microlens characterization is a prerequisite for improving fabrication process, and for satisfying the end user needs. In this paper we explore techniques to characterize geometrical properties of microlens made by thermal reflow: viz. microlens profile; radius of curvature; microlens height; contact angle and focal length. The geometrical characterization is done using techniques such as contact profilometry, scanning electron microscopy (SEM), optical microscopy, white light confocal microscopy and fluorescence confocal microscopy. All the above techniques are studied and compared, keeping in mind the characterization requirements of polymer microlens made by thermal reflow technique.     

A theorem of the Wiener—Tauberian type forL 1(H n)

The Heisenberg motion groupHM(n), which is a semi-direct product of the Heisenberg group Hⁿ and the unitary group U(n), acts on Hⁿ in a natural way. Here we prove a Wiener-Tauberian theorem for L¹ (Hⁿ) with this HM(n)-action on Hⁿ i.e. we give conditions on the “group theoretic” Fourier transform of a functionf in L¹ (Hⁿ) in order that the linear span of^gf : g∈HM(n) is dense in L¹(Hⁿ), where^gf(z, t) =f(g·(z, t)), forg ∈ HM(n), (z,t)∈Hⁿ.     

Injectivity sets for spherical means on the Heisenberg group

We prove that the boundary of a bounded domain is a set of injectivity for the twisted spherical means on ⁿ for a certain class of functions on ⁿ . As a consequence we obtain results about injectivity of the spherical mean operator in the Heisenberg group and the complex Radon transform.     

Computer aided design of inverted strip dielectric waveguide millimeter wave ring-resonator and coupler

A computer aided design technique has been developed for the design of millimeter-wave ring resonator and hybrid-ring coupler using inverted strip dielectric waveguides. The scattering matrix analysis for hybrid-ring coupler has also been developed. Numerical results for these components at f₀=80 GHZ with 3-dB coupling have been presented along with the variation of width, spacing, and radii with frequency.This work was supported by the faculty research committee of the University of North Dakota under research grant no. 1813/0909/2027 and partially funded by E.F. Johnson Co., Waseca, Minnesota, under grant no. 9009/8183.     

Studies on bismuth tungstate and its use as a lead selective inorganic ion-exchanger

Summary A new inorganic ion-exchanger bismuth tungstate has been synthesized. Its composition, chemical stability and ion-exchange properties have been studied. The material shows high selectivity towards Pb²⁺, which has been separated quantitatively from Zn²⁺, Mg²⁺, Ca²⁺, Mn²⁺, Cu²⁺ and Ni²⁺. It also shows electron exchange behaviour with some strong reducing agents.     

Studies on permeation of hydrocarbons through liquid membranes in a continuous contactor

This paper reports experimental studies, in a continuous cocurrent packed column, on the removal of aromatics from hydrocarbon streams by making use of selective transfer through aqueous surfactant membranes. Two types of feed mixtures were used: (i) benzene—heptane and (ii) straight run naphtha from Bombay High crude oil. The receiving phase in both cases was kerosene. The height of a mass transfer unit (HTU) was determined and found to largely lie in the range 2-2.5 m, irrespective of feed composition and solvent/feed ratio. The experimental study confirms the feasibility of a liquid membrane process for dearomatization and provides HTU data for further feasibility and scale-up studies.     

A spectrophotometric determination of 1-naphthol in decimilligram amounts

1-Naphthol is determined by spectrophotometric measurement at 510 nm after oxidation with vanadium(V) in approximately 4M hydrochloric acid and extraction of the oxidation product into toluene.