A Mössbauer effect study of Y(57Fe:Mn)12

The intermetallic compound, YMn₁₂, doped with 0.5at.%⁵⁷Fe has been investigated using the⁵⁷Fe Mössbauer resonance. The data show that the Fe impurities occupy preferentially the f-site at the expense of the i- and j-sites. Whereas the i- and j-sites are expected to carry identical local magnetic moments in the ordered state, low temperature hyperfine fields of 50.08(±0.05)T and 2.90(±0.03)T are measured for the i- and j-sites respectively. It is proposed that large transferred hyperfine fields are responsible for this disparity.     

Short-team stability of trace metals in estuarine water samples

The short-term (up to 24 h) stability of estuarine water with high (22%?) and low (<21%?) salinity, stored unacidified in polythene containers prior to filtration, preservation and determination of dissolved trace metals, was assessed. For the-salinity sample a massive (140%) increase in copper concentration was observed, indicating desorption from the particulate phase; a similar, although less pronounced (11%) effect was found for the high-salinity sample, Evidence was also obtained for a significant loss (30%) of lead from a pre-filtered low-salinity sample, suggesting appreciable adsorption to the container walls. For cadmium and nickel, no substantial changes in concentration were observed.     

Structure elucidation with lanthanide-induced shifts. 4—Bound shifts vs relative shifts

The use of lanthanide shift reagents (LSR's) to obtain additional structural information from nuclear magnetic resonance studies has gained widespread acceptance. However, there has not been general agreement with regard to the most appropriate methodology for analysis of the shifted NMR spectra. We present arguments that only the bound shifts (Δ₁) corresponding to the LS complex should be used for correlation of lanthanide-induced shifts with molecular structure by means of the pseudocontact equation. Several examples are discussed of compounds for which the relative induced shifts are dependent on the concentration of LSR. For such cases it is not possible for both Δ₁ and Δ₂ (the bound shift corresponding to the LS₂ complex) to correlate successfully with the correct structure. Alternative methods of obtaining bound shifts are critically evaluated.     

Experiments with a symbolic programming system for complex analysis

The paper reports the results of work on the construction of LISP programs for various symbolic operations in complex analysis, including the evaluation of integrals around closed contours by the use of Cauchy's Theorem. It is concluded that the only difficulty in the way of the preparation of programs for all of the important and useful textbook calculations in complex analysis is that large amounts of fast storage in the computer are needed.     

Anna Johnson Pell Wheeler: Her life and work

This article describes the life, career, and research of the American mathematician Anna Johnson Pell Wheeler (1883–1966).     

The linear theory of gravitation in the radiation gauge

A global gauge for the linear theory of gravity is given which avoids the (In(R))/R problem of harmonic coordinates. Consequently it is possible to do 1/R expansions for precisely those null sources which lead to difficulties in the harmonic gauge. This is important, for example, in second order calculations where the first order field is a gravitational wave. This gauge makes manifest the two degrees of freedom for the dynamic fields. In it the second time derivative of the metric itself has physical significance since R _oioj=–1/2h_ij.Work supported in part by NSF Grant No. GP-13959.     

Laboratory accreditation in New Zealand

A voluntary system for the registration of testing laboratories was established in New Zealand in 1972. It requires laboratories to meet specific standards, maintain adequate methods manuals and records and exhibit competence in the test methods for which registration is granted. The system also authorizes the endorsement of test documents.     

Excitation dynamics of Rydberg states in C<Subscript>60</Subscript>

The electron and nuclear dynamics of C₆₀ fullerenes irradiated with femtosecond laser pulses are investigated with photoelectron and photoion spectroscopy. The focus of this work is the detailed exploration of the population mechanism of Rydberg levels within the excitation process of neutral C₆₀. The effect of excitation wavelength, intensity, chirp, and polarization on the kinetic energy distribution of photoelectrons in single-pulse experiments gives first insight into the underlying processes. In combination with time-resolved two-color pump-probe spectroscopy depending on either pump, or probe pulse intensity, a more complete picture of the interaction can be drawn. The results point towards a very interesting but nevertheless complex behavior including four steps: (i) non-adiabatic multielectron excitation of the HOMO (h_u) → LUMO+1 (t_1g) transition; (ii) thermalization within the hot electron cloud on a time scale below 100 fs, followed by a coupling of energy to vibrational modes of the molecule via doorway state(s); (iii) population of electronically excited Rydberg states by multiphoton absorption, and (iv) single photon ionization from the excited Rydberg states. This excitation process results in a characteristic sequence of photoelectron lines in the photoemission spectra. The comparison of the experimental results with recent theoretical work gives convincing evidence that non-adiabatic multielectron dynamics (NMED) plays a key role for the understanding of the response of C₆₀ to short-pulse laser radiation.