Magnetic properties of lanthanum orthoferrite fine powders prepared by different chemical routes

Fine powders of lanthanum iron oxide, LaFeO₃, have been prepared by solid state reaction as well as sol-gel synthesis and nebulized spray pyrolysis. Structures, morphologies and magnetic susceptibility measurements of these powders have been examined. The powders prepared by all the three low-temperature routes contain nearly spherical particles with an average diameter of 40 nm. These samples show a lower Neel temperature than the powder prepared by solid state reaction besides showing much lower magnetic susceptibility at low temperatures. Dedicated to Professor C N R Rao on his 70th birthday     

Thermodynamic and surface properties of Sb-Sn and In-Sn liquid alloys

The thermodynamic properties of Sb-Sn and In-Sn liquid alloys have been studied using the quasi-chemical model for compound forming binary alloys and that for simple regular alloys. The concentration fluctuation S _cc(0) and the Warren-Cowley short-range order parameter (α ₁) were determined for the whole concentration range at a temperature of 770 K. The surface tensions of these liquid alloys were determined for the whole concentration range by using energetics determined from thermodynamic calculations. In all calculations, In-Sn manifested properties very close to alloys of ideal mixing, while Sb-Sn showed properties that are asymmetric about equiatomic composition. Our results suggest that a weak complex of the form SbSn₂ could be present in the Sb-Sn alloy at a temperature of about 770 K.     

An algorithm proposed for busy-period subcomponent analysis of bulk queues

This paper presents an algorithmic procedure for a busy-period subcomponent analysis of bulk queues. A component of interest for many server queues is the periodt _k to reduce congestion from a levelk to levelk-1. For anM ^(x)/M/c system with the possibility of total or partial rejection of batches, it is demonstrated that the expected length of busy periods, the proportion of delayed batch and the steady state queue length probabilities can be easily obtained. The procedure is based on the nested partial sums and monotonic properties of expected lengths of the busy periods.Formerly University of Ife.     

Crystal and molecular structure of 1R,3S,5S,7R,10R-3,6,6,10,14-Pentamethyltricyclo[10.3.0.05,7]pentadeca-11,14-diene-1, 10-dihydroxy-2,13-dione (Japodagrol), C20H28O4

A new cytotoxic macrocyclic diterpenoid named Japodagrol, C₂₀H₂₈O₄, has been isolated from the ornamental plantJatropha podagrica, family Euphorbiaceae, grown in Nigeria. The structure of the title compound, C₂₀H₂₈O₄, was solved by X-ray analysis.M _r =332.44, monoclinic space groupC2,a=23.285(4),b=6.5105(12),c=12.505(3) Å,=98.504(17),V=1874.8 ų,Z=4,D _c =1.178 Mg/m³. CuK radiation (graphite crystal monochromator, =1.54184 A), (CuK)=6.13 cm^–1,F(000)=720,T=290 K. Final conventionalR factor=0.035,R _w =0.038 for 3349 observed reflections. The structure was solved with the programDirdif. The 5-membered ring is closed to a half-chair form. The compound contains inter- and intramolecular hydrogen bonds.     

Searching for light Higgs scalar bosons in the next generation of electron-positron collider at LEP

Thee ⁺ e ^–-collider facilities at LEP II, with the CM energy S in the range 100–170 GeV, may be able to detect light Higgs bosons, assuming a high luminosity. The production cross sections of a light Higgs bosonH ⁰ in association with the neutral gauge bosonZ ⁰ are calculated for varying ranges of the CM energy expected to be available to LEP II and VLEEP (Novosibirsk) and for various values of the light Higgs mass. It is found that production cross sections are sizable in comparison with those for the very massive Higgs bosons in proton-anti(proton) supercolliders, Tevatron, Sp¯pS, and SSC, respectively. The implication of this feature is pointed out. Further, prospects for light Higgs production in association with the charged gauge bosonW ^– in ultraenergetic neutrino beams are examined.     

Novel strategy for constant-distance imaging using alternating current scanning electrochemical microscopy

Scanning electrochemical microscopy (SECM) still lacks reliable means for performing constant-distance imaging experiments. We demonstrate, for the first time, that the same negative alternating current (AC) feedback can be observed on approach to an insulator and an unbiased conductor at optimal experimental conditions. This leads to a novel constant-distance imaging mode. To perform AC-SECM imaging, only minor modifications of the existing SECM set-up were necessary. The new constant-distance AC-SECM imaging was conducted to provide topographical information not affected by variations in sample conductivity and reactivity. Furthermore, simultaneous AC and DC SECM measurements were carried out to demonstrate that both topographical and chemical information could be revealed.     

Effect of Inorganic Ions on Oleate Adsorption at a Nigerian Hematite–Water Interface

Using “pure” natural hematite selected from a high silica Nigerian hematitic ore, oleate adsorption densities at the hematite–water interface were determined in the presence of various inorganic ions (anions and cations) of different charges and at varying concentrations. Adsorption density was determined using electrical conductivity measurements. The specific surface area of the hematite particles was determined using the method of adsorption of paranitrophenol in aqueous solution. Inorganic ions in solution depressed oleate adsorption at the aqueous hematite surface. The charge of the ion proved to be the dominant factor determining the depression of oleate adsorption. Ionic strength also was an influence, up to a limiting value at which monolayer oleate coverage of the hematite surface occurred. The inorganic ions in solution are considered to function through nonspecific adsorption in the diffuse region of the electric double layer.     

Properties of molten carboxylates part 5. A quantitative differential thermal analysis study of mesophase formation in the sytems lead(II)dodecanoate/lead(II) oxide and lead(II)dodecanoate/hendecane

Measurements have been made of the temperatures and enthalpy changes of phase transitions in the systems lead dodecanoate/lead oxide and lead dodecanoate/hendecane. The data have been discussed in terms of the R theory of amphiphylic mesophases. The concepts of the R theory are shown to be useful in the interpretation of phase transitions in molten carboxylate systems.     

The reaction of iodine monochloride and monobromide with tetraorganotins

The reactions of iodine monochloride and iodine monobromide with a tetraalkyltin (butyl) and a tetraaryltin (phenyl) have been studied with a view to establishing their utility as routes to organotin chlorides and bromides respectively. Rapid high yield syntheses of the triorganotin bromides, diorganotin dichlorides and trialkyltin chloride were achieved. Some further suggestions are made on the mechanism of interhalogen fission of tincarbon bonds.     

Pyrolytic decomposition of some even chain length copper (II) carboxylates

The products of the pyrolytic decomposition of some even chain-length copper (II) carboxylates from decanoate to octadecanoate inclusive have been identified, using a flow system, to be copper, carbon dioxide, a carboxylic acid and an odd chain-mength alkene. These products are similar to those reported for the decomposition of mercury (II) carboxylates. The unexpectedly low (less than unity) CO₂/soap ratio was attributed to the reduction of the CO₂ to carbon monoxide. The carboxylic acid was characterised by wet chemical tests, determining the melting points of the acid and its amide derivative and matching its IR spectrum with that of the authentic acid. Elemental analysis and wet chemical tests were employed for the identification of the alkene.The products of decomposition and mechanism proposed to account for the degradative route of the systems show that good quality thin solid copper oxide films may only be obtained from the decomposition of copper (II) carboxylates if the carrier gas is non-inert (e.g. oxygen).

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Zusammenfassung Als Produkte der pyrolytischen, in einem Gasstrom vorgenommenen Zersetzung einiger Kupfer (II) -Karboxylate mit geradzahliger Kohlenstoffatomzahl der Kette (Dekanoat bis einschließlich Octadekanoat) wurden Kupfer, Kohlendioxid, eine Karbonsäure und ein Alken mit ungerader Kohlenstoffatomzahl identifiziert. Diese Produkte sind ähnlich denen, die bei der Zersetzung von Quecksilber (II) -Karbcxylaten auftreten. Das unerwartet niedrige CO₂/Seife-Verhältnis (kleiner als 1) wurde der Reduktion von CO₂ zu Kohlenmonoxid zugeschrieben. Die Karbonsäure wurde durch naße chemische Tests, durch Bestimmung des Schmelzpunktes der Säure und dem des Amidderivats und durch Vergleich des IR-Spektrums mit dem der authentischen Säure identifiziert. Elementaranalyse und naße chemische Tests wurden zur Identifizierung der Alkene herangezogen. Die Zersetzungsprodukte und der zur Erklärung des Abbaus des Systems vorgeschlagene Mechanismus zeigen, daß dünne feste Kupferoxidschichten in guter Qualität nur bei der Zersetzung von Kupfer (II) -Karboxylaten in nichtinertem Trägergas (z. B. in Sauerstoff) erhalten werden.

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