Chemical separation and electrothermal atomic-absorption spectrophotometric determination of Cd, Co, Cu and Ni in high-purity uranium

Summary An electrothermal atomic-absorption spectrophotometric method has been developed for the estimation of trace concentrations of Cd, Co, Cu and Ni in high-purity uranium after their chemical separation. The trace constituents from 100 mg of uranium sample in 3 M nitric acid solution were separated using 0.2 M di-n-octyl sulphoxide in xylene. The concentration of the analytes in the aqueous phase was determined by graphite furnace AAS. The detection limits were 0.001, 0.01, 0.025 and 0.05 ng for Cd, Co, Cu and Ni, respectively. The precision of the determinations was 7–14%. The effect on absorbances of the analytes due to the presence of Al, Ca, Fe, Mg, Pb, W and uranium was examined.

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Chemische Abtrennung und elektrothermische AAS-Bestimmung von Cd, Co, Cu und Ni in hochreinem Uran

Zusammenfassung Die Spuren werden aus einer 100 mg Uranprobe in 3 M salpetersaurer Lösung durch Extraktion des U mit Hilfe von 0.2 M Di-n-octylsulfoxid im Xylol abgetrennt und werden anschließend in der wäßrigen Phase durch Graphitofen-AAS bestimmt. Die Nachweisgrenzen betragen 0,001 ng (Cd), 0,01 ng (Co), 0,025 ng (Cu) und 0,05 ng (Ni). Die Reproduzierbarkeit beträgt 7–14%. Der Einfluß von Al, Ca, Fe, Mg, Pb, W sowie Resturan auf die Absorption der analysierten Elemente wurde untersucht.

     

Evidence for formation of the first excited state of positronium

Evidence based on positronium 2γ annihilation radiation is reported for the formation of the n=2 state of positronium in a gas by optical excitation from the n=1 state.     

Temperature dependence of ultrasonic propagation speed and attenuation in excised canine liver tissue measured using transmitted and reflected pulses

Previous reported data from our laboratory demonstrated the temperature dependence of propagation speed and attenuation of canine tissue in vitro at discrete temperatures ranging from 25 to 95 degrees C. However, concerns were raised regarding heating the same tissue specimen over the entire temperature range, a process that may introduce irreversible and, presumably, cumulative tissue degradation. In this paper propagation speed and attenuation vs temperature are measured using multiple groups of samples, each group heated to a different temperature. Sample thicknesses are measured directly using a technique that uses both transmitted and reflected ultrasound pulses. Results obtained using 3 and 5 MHz center frequencies demonstrate a propagation speed elevation of around 20 m/s in the 22-60 degrees C range, and a decrease of 15 m/s in the 60-90 degrees C range, in agreement with previous results where the same specimens were subjected to the entire temperature range. However, sound speed results reported here are slightly higher than those reported previously, probably due to more accurate measurements of sample thickness in the present experiments. Results also demonstrate that while the propagation speed varies with temperature, it is not a function of tissue coagulation. In contrast, the attenuation coefficient depends on both tissue coagulation effects and temperature elevation.     

Extension of sensing distance in a ROTDR with an optimized fiber

A sensing fiber, with a gradually increasing Raman-gain-coefficient (g_R/A_eff)along the fiber length, and which can keep the received Raman Stokes power constant in a distributed Raman-based Fiber-optic temperature Sensor, is proposed. This method can be an additional and easy way to further extend the sensing distance of the distributed Raman Fiber-optic temperature Sensor.     

Topology and H-flux of T-dual manifolds

We present a general formula for the topology and H-flux of the T-dual of a type II compactification. Our results apply to T-dualities with respect to any free circle action. In particular, we find that the manifolds on each side of the duality are circle bundles whose curvatures are given by the integral of the dual H-flux over the dual circle. As a corollary we conjecture an obstruction to multiple T-dualities, generalizing the obstruction known to exist on the twisted torus. Examples include SU(2) Wess-Zumino-Witten models, lens spaces, and the supersymmetric string theory on the nonspin AdS5 x CP2 x S1 compactification.     

Hydroboration of Alkynes with Zwitterionic Ruthenium–Borate Complexes: Novel Vinylborane Complexes

Building upon previous studies on the synthesis of bis(sigma)borate and agostic complexes of ruthenium, the chemistry of nido‐[(Cp*Ru)₂B₃H₉] ( 1 ) with other ligand systems was explored. In this regard, mild thermolysis of nido‐ 1 with 2‐mercaptobenzothiazole (2‐mbzt), 2‐mercaptobenzoxazole (2‐mbzo) and 2‐mercaptobenzimidazole (2‐mbzi) ligands were performed which led to the isolation of bis(sigma)borate complexes [Cp*RuBH₃L] ( 2 a – c ) and β‐agostic complexes [Cp*RuBH₂L₂] ( 3 a – c ; 2 a , 3 a : L=C₇H₄NS₂; 2 b , 3 b : L=C₇H₄NSO; 2 c , 3 c : L=C₇H₅N₂S). Further, the chemistry of these novel complexes towards various diphosphine ligands was investigated. Room temperature treatment of 3 a with [PPh₂(CH₂)_nPPh₂] (n=1–3) yielded [Cp*Ru(PPh₂(CH₂)_nPPh₂)‐BH₂(L₂)] ( 4 a – c ; 4 a : n=1; 4 b : n=2; 4 c : n=3; L=C₇H₄NS₂). Mild thermolysis of 2 a with [PPh₂(CH₂)_nPPh₂] (n=1–3) led to the isolation of [Cp*Ru(PPh₂(CH₂)_nPPh₂)(L)] (L=C₇H₄NS₂ 5 a – c ; 5 a : n=1; 5 b : n=2; 5 c : n=3). Treatment of 4 a with terminal alkynes causes a hydroboration reaction to generate vinylborane complexes [Cp*Ru(R?C?CH₂)BH(L₂)] ( 6 and 7 ; 6 : R=Ph; 7 : R=COOCH₃; L=C₇H₄NS₂). Complexes 6 and 7 can also be viewed as η‐alkene complexes of ruthenium that feature a dative bond to the ruthenium centre from the vinylinic double bond. In addition, DFT computations were performed to shed light on the bonding and electronic structures of the new compounds.     

Ultrastiff cubic TiO2 identified via first-principles calculations

The crystal structures and compressibilities of fluorite- and pyrite-structured TiO2 under varying hydrostatic pressures are calculated using gradient-corrected density functional as well as hybrid density functional-Hartree-Fock formulations. The results suggest that fluorite TiO2 is a highly incompressible solid with a large bulk modulus value (K(0) approximately 395 GPa), approaching that of ultrahard cotunnite TiO2 (K(0)=431 GPa). The bulk modulus obtained for pyrite TiO2 is considerably smaller (K(0) approximately 220-260 GPa), nonetheless larger than the value determined experimentally for cubic TiO2. Calculated shear modulus values indicate that fluorite TiO2 has the potential to be an ultrahard material, if it could be stabilized under ambient conditions.     

Synthesis and structures of cross-conjugated bis-dehydroannulenes with a Y-enediyne motif and different pi topologies

A synthesis of cross-conjugated bis-dehydroannulenes with different topologies of the pi electrons by Cu(II)-mediated oxidative coupling of the corresponding terminal acetylenic precursors is reported. In general, of the two possible modes of cyclization, which would yield either a [13]annulene or an [18]annulene, the precursors yielded exclusively the bis-dehydro[13]annulenes. However, one example of the formation of a bis-dehydro[18]annulene is also reported. The mode of cyclization to form either the [13]annulene or the [18]annulene is explained on the basis of the conformational preference of the core unit bearing the Y-enediyne moieties. The structures of the two types of bis-annulenes have been unequivocally established by means of single-crystal X-ray crystallographic analysis.     

Vibrational spectroscopic studies and ab initio calculations of 5-methyl-2-(p-fluorophenyl)benzoxazole

FT-Raman and FT-IR spectra of 5-methyl-2-(p-fluorophenyl)benzoxazole were recorded and analysed. The vibrational frequencies of the compound have been computed using the Hartree-Fock/6-31G* basis and compared with the experimental values.