Trace metal assay of thorium oxide by atomic emission spectrometry

Summary An Atomic Emission Spectrometric (AES) method has been developed for the direct determination of twenty-two metallic elements at trace concentrations in thorium oxide. The method is based on the use of a d.c. arc — carrier distillation technique with 12% composition of a mixed carrier, viz. AgCl+SrF₂ in 5:1 proportion, and is equally applicable to both volatile and refractory analytes. A direct reading emission spectrometer with computerised data acquisition and processing facility has been used in these studies. The standardisation procedure includes study of volatilisation/excitation characteristics of the analyte elements to optimise choice and proportion of the carrier and signal integration time apart from optimisation of other experimental parameters such as arc current, viewing position of the arc plasma, sample charge etc. The detection limits for the analytes lie in the range 0.1–50 ppm while the precision of determinations is better than 15% for most of the elements as evaluated from the repetitive analyses of spiked samples.     

Alcaloides steroidiques—LII Alcaloides du buxus balearica Willd.: Cycloprotobuxine-D, buxamine-E, buxaminol-E, N-isobutyryl-baleabuxidine-F, N-benzoyl-baleabuxidine-F, baleabuxoxazine-C, N-isobutyryl-baleabuxidienine-F, N-benzoyl-baleabuxidienine-F, N-isobutyryl-baleabuxaline-F

The following alkaloides have been extracted from the leaves of Buxus balearica Willd.: cyclomicrophylline-B, cycloprotobuxines A, C and D, baleabuxine (N-isobutyryl-baleabuxine-F), buxamine-E and buxaminol-E (already reported), N-isobutyryl- and N-benzoyl-baleabuxidine-F, baleabuxoxazine-C, N-isobutyryl- and N-benzoyl-baleabuxidienine-F, N-isobutyryl-baleabuxaline-F, the structures of which are proposed. The stereochemistry of baleabuxidines and baleabuxoxazines is established on the base of chemical correlations between these two groups and cyclomicrophyllines.     

Black hole formation in a box

Evidence is presented for Hawking's viewpoint that in an insulated box in thermal equilibrium, black holes should form and evaporate in a statistically time-symmetric way. In particular, it is shown that if a black hole can evaporate adiabatically, it is much more likely to form adiabatically than by Jeans instability.     

Structural chemistry of Magnéli phases TinO2n−1 (4 ≤ n ≤ 9). III. Valence ordering of titanium in Ti6O11 at 130 K

The phase transition at 147 K in Ti₆O₁₁ corresponds to the occurrence of a superstructure with tripling of the cell volume on cooling. Its reduced cell parameters at 130 ± 5 K are a = 7.517(1), b = 11.986(2), c = 13.397(2) Å, α = 98.29(1), β = 105.52(1), and γ = 107.79(1) degrees in space Group $\text{P}\text{1}$ with Z = 6. A systematic nomenclature adding one index to the substructure atom names permits calculation of the model's atomic coordinates in the asymmetric unit in terms of the rutile sub-substructure and keeps track of the structural changes. The superstructure was solved by direct methods and refined to R_F = 5.2% on 3062 observed reflections assuming isotropic thermal motion. A complex pattern of TiO and TiTi distance changes is observed. It is interpreted to correspond to valence ordering of the Ti atoms, probably complete in the shear-plane slab and partial in the rutile-like slab. The TiTi distances, with one very short approach of 2.65 Å at a shared face, seem to be consistent with “bipolarons” but can also be analyzed in terms of electrostatic repulsion which allows for the considerable lengthening of some distances as well.     

The determination of eear elements in aircraft engine oil filter debris by neutron activation analysis

The increasing trend towards the use of fine oil filtration in modern jet engines suggests that the Spectrometric Oil Analysis Program (SOAP), which routinely monitors the health of aeroengines, may no longer be effective in detecting abnormal wear trends. Since the oil filter contains a wealth of information on wear in a system, it may be necessary to perform engine health monitoring through Filter Debris Analysis (FDA). In the present study, a method was developed for the determination of 19 wear elements (Ag, Al, Au, Cd, Co, Cr, Cu, In, Fe, Mg, Mn, Mo, Ni, Sb, Sn, Ti, V, W and Zn) in aircraft engine oil filter debris samples using the analytical technique of Neutron Activation Analysis (NAA). Results obtained by NAA for the analysis of two types of filter debris samples compared well with results obtained previously for similar samples and it appears that FDA should be very useful for following wear trends.     

Is quantum gravity deterministic and/or time symmetric?

S. W. Hawking suggests that quantum gravity introduces a new level of uncertainty into physics by turning pure states into mixed states. Although the evidence for this information loss is based upon a semiclassical approximation and hence is not conclusive, it is interesting to examine the implications. As originally formulated, Hawking's proposal violates CPT invariance by singling out one direction of time in which pure states turn into mixed states. An alternate hypothesis is suggested whereby the theory could be time symmetric and yet allow a loss of information. In this model the universe as a whole would be an open system, and even its density matrix would not have a deterministic evolution. The question remains of how much uncertainty there actually is in quantum gravity.     

Rollover risk and endogenous network dynamics

Using a dynamic network formation model, solved numerically, we study banks’ rollover decisions. We find that when the existence of linkages between market participants generates an informational externality, the newly formed network is conditioned by past architectures. Moreover, this inertia is strongly dependent on macroeconomic conditions, such as investors’ risk appetite. Simulations show that for intermediate values of the risk appetite’s parameter the financial network exhibits tipping points, i.e., the inability to maintain a threshold number of linkages may push the market into a gridlock. In this context, we study also how policy instruments, such as taxes and subsidies, affects debt rollover. Since a reduction in the policy level plays the same role as an improvement in economic fundamentals, the creation of interbank connections can be stimulated by it. Thus, in order to restart lending after a major stress situation in the interbank market a considerable reduction in the policy level is required, advising a counter-cyclical policy similar to the ones recently proposed with respect to capital requirements.