Mössbauer and magnetic studies in nickel ferrite nanoparticles: Effect of size distribution

The magnetic properties of nickel ferrite nanoparticles in the form of powders, prepared by the sol-gel process and subjected to different annealing temperatures, were investigated using both static and dynamic measurements namely hysteresis, zero field cooled-field cooled magnetization (ZFC-FC) measurements and Mössbauer spectroscopy. The Transmission Electron Microscopy (TEM) studies reveal particle sizes for the as-prepared particles which increases upto 52 nm with annealing. A bimodal distribution, upto an annealing temperature of was observed. ZFC-FC measurements for the as-prepared samples reveal twin peaks, indicative of the bimodal size distribution. ZFC-FC measurements performed for fields varying from 100 Oe to 3 kOe show a superparamagnetic phase with blocking temperatures between 320 and . Numerical simulations for the ZFC-FC studies indicate that the signature of the bimodal size distribution can be seen only at very low fields. The variation of coercivity with particle size, as determined from the hysteresis measurements, shows a transition from a single domain to a multi domain state for particle sizes larger than 35 nm. Mössbauer measurements performed at room temperature for the as-prepared sample shows a six finger pattern for the samples with higher particle size and a doublet pattern for the samples with smaller particle size, which is indicative of their superparamagnetic nature.     

All Solid State Chromium(III) Selective Potentiometric Sensor Based on 2‐(1‐(2‐((3‐(2‐Hydroxyphenyl)‐1H‐pyrozol‐1‐yl)methyl)benzyl)‐1H‐pyrazol‐3‐yl)phenol

Highly selective all solid state electrochemical sensor based on a synthesized compound i.e. 2‐(1‐(2‐((3‐(2‐hydroxyphenyl)‐1H‐pyrozol‐1‐yl)methyl)benzyl)‐1H‐pyrazol‐3‐yl)phenol (I) as an ionophore has been prepared and investigated for the selective quantification of chromium(III) ions. The effect of various plasticizers, viz. dibutyl phosphonate (DBP), dibutyl(butyl) phosphonate (DBBP), nitrophenyl octyl ether (NPOE), tris‐(2‐ethylhexyl)phosphonate (TEP), tri‐butyl phosphonate (TBP), dioctyl phthalate (DOP), dioctyl sebacate (DOS), benzyl acetate (BA) and acetophenone (AP) along with anion excluders NaTPB (sodium tetraphenyl borate) and KClTPB (potassium(tetrakis‐4‐chlorophenyl)borate was also studied. The optimum composition of the best performing membrane contained (I):KClTPB:NPOE:PVC in the ratio 15 : 3 : 40 : 42 w/w. The sensor exhibited near Nernstian slope of 20.1±0.2 mV/decade of activity in the working concentration range of 1.2×10^?7–1.0×10^?1 M, and in a pH range of 3.8–4.5. The sensor exhibited a fast response time of 10 s and could be used for about 5 months without any considerable divergence in potentials. The proposed sensor showed very good selectivity over most of the common cations including Na⁺, Li⁺, K⁺, Cu²⁺, Sr²⁺, Ni²⁺, Co²⁺, Ba²⁺, Hg²⁺, Pb²⁺, Zn²⁺, Cs⁺, Mg²⁺, Cd²⁺, Al³⁺, Fe³⁺and La³⁺. The activity of Cr(III) ions was successfully determined in the industrial waste samples by using this sensor.     

Determination of biogenic amines in lake water by micellar electrokinetic chromatography with fluorescence detection after derivatization with fluorescamine

A simple and rapid method has been developed for the determination of biogenic amines in lake water using micellar electrokinetic chromatography with fluorescence detection. Separation of fluorescamine derivatized biogenic amines was accomplished by using borate buffer of pH 9.5 containing 40 mM of sodium dodecyl sulphate. The method has been optimized with respect to fluorescamine concentration, reaction pH, reaction time, separation voltage and injection time. Detection was performed by using UG-11 excitation filter and 495 nm emission filter. The proposed method for histamine, tyramine and dopamine allowed their separation within 2 min with detection limits in nM range. The interday and intraday reproducibility of peak areas were less than 6.5%. Recovery of spiked samples was 95.76–116.31%.     

X-Ray Crystal Structure of 25-O-Deacetyl-27, 28-didehydro-27-demthoxy-11-deoxo-11, 29-epoxy-28,29-dihydro-21,23-O-isopropylidenerifamycin S

In search of new types of semisynthetic derivatives of the natural antibiotic rifamycin S ( 1 ), we synthesized 25-O-deacetyl-27,28-didehydro-27-demethoxy-11-deoxo-11,29-epoxy-28, 29-dihydro-21,23-O-isopropyli-denerifamycin S ( 3 ). Its X-ray crystal structure shows a new type of ansa-chain with an 11,29-epoxy moiety, the loss of the MeO group on C(27), and the shift of the C?C bond from C(28),C(29) to C(27),C(28). These modifications result in a conformational rearrangement of the whole ansa-chain, nonetheless the overall spatial shape of the molecule is still close to that of most rifamycins. As found in other 11-deoxo-11-hydroxyrifamycin-S derivatives, the chromophore rings of 3 give rise to π-π association in the crystal.     

Single domain magnetic arrays: role of disorder and interactions

The hysteresis of an array of interacting single domain magnetic particles is studied, where the particles interact via exchange and dipolar interactions. The dependence of the magnetic properties on the distribution of grain sizes, the density of the grains, the anisotropy energy and the exchange interactions in the array is investigated through Monte Carlo simulations for nanoparticle systems. We also present some experimental results on the -polypyrrole nanocomposite system which agree with the trends observed in our simulations.Received: 29 January 2004, Published online: 18 June 2004PACS: 75.75. + a Magnetic properties of nanostructures - 75.50.Lk Spin glasses and other random magnets - 75.40.Mg Numerical simulation studies - 75.50.Tt Fine-particle systems; nanocrystalline materials     

Stylized facts from a threshold-based heterogeneous agent model

A class of heterogeneous agent models is investigated where investors switch trading position whenever their motivation to do so exceeds some critical threshold. These motivations can be psychological in nature or reflect behaviour suggested by the efficient market hypothesis (EMH). By introducing different propensities into a baseline model that displays EMH behaviour, one can attempt to isolate their effects upon the market dynamics. The simulation results indicate that the introduction of a herding propensity results in excess kurtosis and power-law decay consistent with those observed in actual return distributions, but not in significant long-term volatility correlations. Possible alternatives for introducing such long-term volatility correlations are then identified and discussed.     

The Formation of 8‐Epipodocarp‐9(11)en‐12‐one in the Course of the Preparation of Podocarp‐9(11)‐en‐12‐one from O‐Methylpodocarpane and Related Studies

The preparation of podocarp‐9(11)‐en‐12‐one ( 1a ) from O‐methylpodocarpane ( 2 ) was investigated with the aim of clarifying whether 8‐epipodocarp‐9(11)‐en‐12‐one ( 1b ) is formed to any extent during the early stages of the process. This study, supported by molecular‐mechanics calculations, resulted in the preparation, along with 1a , of the previously undescribed 1b , which could be fully characterized by means of 2D‐NMR experiments. Significant differences recorded in the NMR and NOESY spectra of 1a and 1b were of diagnostic value in establishing the relative configuration at C(8) and possibly might be helpful to solve similar problems on podocarp‐9(11)‐en‐12‐one derivatives.