Critical phenomena in FINEMET alloy

The Fe_73.5Cu₁Nb₃Si_13.5B₉ FINEMET alloy has been prepared by the rapid solidification technique. The critical behaviour of this alloy in the amorphous as well as in its nanocrystalline states has been studied near their respective Curie temperatures. From the values of the critical exponents one can conclude that the alloy behaves like a 3D Heisenberg ferromagnet in the amorphous and nanocrystalline states. But there exists a slight increase in the value of β for the alloy annealed at 823 K (the nanocrystalline state) as observed in most of the amorphous alloys.     

PIV studies of large scale structures in the near field of small aspect ratio elliptic Jets

The near flow field of small aspect ratio elliptic turbulent free jets (issuing from nozzle and orifice) was experimentally studied using a 2D PIV Two point velocity correla tions in these jets revealed the extent and orientation of the large scale structures in th e major and minor planes. The spatial filtering of the instantaneous velocity field using Gaussian convolution kernel shows that while a single large vortex ring circumscribing the jet seems to be present at the exit of nozzle, the orifice jet exhibited a number of smaller vortex ring pairs close to jet exit. The smaller length scale observed in the case of the orifice jet is rep resentative of the smaller azimuthal vor tex rings that generate axial vortex field as they are convected. This results in the axis-switching in th e case of orifice jet and may have a mechanism differ ent from the self induction process as observed in the case of contoured nozzle jet flow.     

Subtilisin catalysis of substrate anchored in cyclodextrin

The N-benzoyl-l-tyrosine ethyl ester (BTEE) anchored in cyclodextrin (β and β-methyl CD) serves as an excellent substrate for subtilisin Carlsberg catalysis. The rate of hydrolysis was found to be approximately twofold higher than that of the methanolic substrate. The K_mapp and V_max values for the CD anchored substrates were significantly higher than the methanol-solubilized BTEE.     

(1-Adamantanethio)pyridines and tetrahydropyridines from the reaction of 1-adamantanethiol with pyridine I-oxide in acetic anhydride

The reaction of pyridine 1-oxide with 1-adamantanethiol in acetic anhydride produced a mixture of 2- and 3-(1-adamantanethio)pyridines, 1-aeetyl-2-(1-adamantanethio)-3-hydroxy-4-acetoxy-1,2,3,4-telrahydropyridine and the corresponding 3-acetoxyderivative. Pure substances were separated by means of column chromatography on alumina. The tetrahydropyridines were identified by means of their proton magnetic and mass spectra. 4-(1-Adamantanethio)pyridine was synthesized from 4-chloropyridinc and 1-adamantanethiol. The three isomeric (1-adamantanethio)-pyridines were, each, cleaved by concentrated hydrochloric acid to give 1-chloroadamantane and the corresponding pyridinethiol.     

Studies in oxidation-reduction reactions: Oxidation with chloramine-b indirect determinations

Chloramine-B has been used as an oxidizing agent in hydrochloric acid medium for the indirect volumetric estimations of hydrogen peroxide, lead dioxide, manganese dioxide, selenium dioxide, sodium formate, sodium sulphide, sodium metavanadate, potassium iodate and copper sulphate using iodine monochloride as a catalyst and pre-oxidiser. Chloroform is used as an indicator. It is coloured pink owing to the liberation of iodine during the titration and becomes light pale yellow at the end-point because of the formation of iodine monochloride.     

Ammonium tetraphenylborate-naphthalene adsorbent for the preconcentration and trace determination of iron in alloys and biological samples using 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol by third derivative spectrophotometry

A solid ion-pair material produced from ammonium tetraphenylborate on naphthalene (ATPB-naphthalene) provides a simple, rapid, economical and selective technique for preconcentrating iron from approximately 500 ml of aqueous solution of standard alloys and biological samples. Iron reacts with 2-(5-bromo-2-pryidlazo)-5-diethylaminophenol (5-Br-PADAP) to form a water-soluble cationic complex. When the aqueous solution of this cationic species in the pH range 3.2-8.5 is passed over the adsorbent ATPB-naphthalene at a flow rate of 1 ml min(-1), it is quantitatively retained on naphthalene as an uncharged ion-associated complex. The solid mass from the column was dissolved out with 5 ml of dimethylformamide (DMF) and iron is determined by third derivative spectrophotometry by measuring the signal d(3)A/ dlambda(3) between lambda(2)(773 nm) and lambda(3)(737 nm). The calibration curve is linear over the concentration range 0.10-25.0 mug of iron in 5 ml of DMF solution. Eight replicate determinations of 5 mug of iron gave a mean intensity (peak-to-peak signal between lambda(2) and lambda(3)) of 1.534 with a relative standard deviation of 0.90%. The sensitivity of the method is 0.307 (d(3)A/dnm(3) )/mug found from the slope of the calibration curve. The interference of a large number of anions and cations has been studied and the optimized conditions developed were utilized for the trace determination of iron in various standard alloys and biological samples.     

Transport of excitation energy in a doped molecular aggregate. III. numerical investigation of exciton hopping with various exciton-depleting processes

A brute-force numerical investigation has been carried out on the hopping of excitons in a three-dimensional molecular aggregate. Possibilities of vibronic decay, rapid chemical reactions of saturated species, radiative decay of overpopulated molecules, and cooperative chemical reactions involving saturated exciton populations on traps of two different types have been considered. Investigation have been performed with two types of initial distribution of excitons—facial and random—and for 10,000 or, sometimes, for 20,000 time steps each of duration 1ps. Several interesting observations have been made from this computer experiment: (1) The total number of occurrences of fast reactions depends upon the initial distribution of excitons. (2) It decreases if other exciton depleting processes are at work. (3) It also depends on the pattern of placement of traps. (4) The location of impurities also affects the rate of occurrence of these reactions. Thus, more reactions occur when the excitons are initially concentrated on one face and traps are suitably located on the path of flow of these excitons. A random initial distribution tends to equilibrate the excitons quickly over all the lattice points, thus giving rise to fewer reactions. (5) The number of reactions need not necessarily increase with the number of reaction centers; in fact, it decreases as more centers are added when the supply of excitons is severely limited. (6) A Complicated dynamics results when different types of additional processes, viz., enhanced fluorescence, radiative emissions, and cooperative chemical reactions are simultaneously allowed. The cooperative process has been clearly found to dominate. A first-order rate constant of about 10⁸ s-¹ has been calculated for the occurrence of the cooperative process. This rate is affected when other nonconserving processes are switched on. Observations (1), (4), and (5) are the most important conclusions of our work. They lie outside the scope of traditional models such as the random walk model, the diffusion model, and the lattice model for the migration of excitons in a molecular aggregate. © 1993 John Wiley & Sons, Inc.     

E.s.r. studies on acylhydrazine and hydrazone copper(II) sulfate complexes

Summary Cu^II complexes of the [CuL₂(SO₄)]·nH₂O and [CuL(SO₄)(H₂O)₂]·nH₂O type, where L = benzoylhydrazine (PhCONHNH₂; BH) or iso-propanone benzoylhydrazone (PhCONHN:CMe₂; IBH), L= iso-nicotinoylhydrazine (NC₅H₄CONHNH₂; INH) or isopropanone iso-nicotinoylhydrazone (NC₅H₄CONHN: CMe₂; IINH); n = 0–2, were prepared and characterized by elemental analyses, molar conductances, and electronic, e.s.r. and i.r. spectral measurements. The electronic and e.s.r. spectra suggest a tetragonally distorted octahedral geometry in the solid state as well as in DMSO solution. The e.s.r. data also reveal an axial symmetry for most of the complexes in the solid state and in DMSO solution at 300 and 77 K, while the complex of IBH is isotropic at 300 K. The M_s = 2 transition observed for this complex suggests that it is a dimer. BH and INH bond to Cu^II through the C-O and NH₂ groups, whereas IBH and IINH bond through C-O and C-N groups.     

Spin density distributions in radical anions of heterocyclic amine N-oxides

The unrestricted Hartree-Fock (UHF) method of Snyder and Amos is used to calculate, in the -electron approximation, the spin density distributions in radical anions of heterocyclic amine N-oxides. The computed spin densities are observed to be in good agreement with the experimental values. The computed spin density distribution of the radical anion of pyridine N-oxide is consistent with the greater susceptibility of pyridine N-oxide relative to pyridine to electrophilic nitration. Also, the calculations are consistent with the lower basicity of the N-oxides relative to the parent bases.     

Extraction of uranium(VI) and plutonium(IV) with dihexylbutyramide and dihexylisobutyramide from nitric acid medium

The extraction of uranium(VI) and plutonium(IV) was carried out with two isomeric monoamides, dihexylbutyramide (DHBA) and dihexylisobutyramide (DHIBA) from nitric acid medium, usingn-dodecane as diluent. The possibility of separation of the two metal ions from each other without valency adjustment was attempted. U(VI) was extracted as its disolvate, while Pu(IV) was extracted as its trisolvate. From the variation of distribution ratio with temperature, it was shown that the extraction reaction was enthalpy controlled in all the cases.