Propagation of avalanches in Mn12-acetate: magnetic deflagration

Local time-resolved measurements of fast reversal of the magnetization of single crystals of Mn12-acetate indicate that the magnetization avalanche spreads as a narrow interface that propagates through the crystal at a constant velocity that is roughly 2 orders of magnitude smaller than the speed of sound. We argue that this phenomenon is closely analogous to the propagation of a flame front (deflagration) through a flammable chemical substance.     

Interlaboratory evaluation of hydrophone sensitivity calibration from 0.1 to 2 MHz via time delay spectrometry

Knowing the low-frequency response of hydrophones, down to 100 kHz at least, is important for accurate biomedical ultrasound measurements. However, current international standards do not extend below 500 kHz. Furthermore, commercial hydrophone sources typically do not supply sensitivity data below 1-2 MHz. Therefore, to help identify and validate practical calibration methods below 2 MHz, the authors have extended their previous individual efforts in an interlaboratory evaluation of sensitivity calibration using the swept-frequency technique, time delay spectrometry (TDS). Calibrations were performed for needle and membrane PVDF hydrophones using each laboratory's TDS system. Each site employed the same purpose-built broadband source transducers, comprising both plano-concave and biconcave 1-3 piezocomposite elements 4 cm in diameter, with maximum and minimum thicknesses of approximately 1.5 and 0.1 cm. Agreement between laboratories was within the estimated measurement precision of +/-0.6 dB. The results demonstrated that a TDS system employing such transducers constitutes a viable method for hydrophone calibrations in this frequency range.     

Nonlinear propagation model for ultrasound hydrophones calibration in the frequency range up to 100 MHz

To facilitate the implementation and verification of the new ultrasound hydrophone calibration techniques described in the companion paper (somewhere in this issue) a nonlinear propagation model was developed. A brief outline of the theoretical considerations is presented and the model's advantages and disadvantages are discussed. The results of simulations yielding spatial and temporal acoustic pressure amplitude are also presented and compared with those obtained using KZK and Field II models. Excellent agreement between all models is evidenced. The applicability of the model in discrete wideband calibration of hydrophones is documented in the companion paper somewhere in this volume.     

The creation of actuarial science

Actuarial science was created more than 300 years ago. The article traces the influences which led to this development, which has been of such fundamental significance for calculations involving risk and finance and has enabled life assurance companies and pension funds to be financed on scientific principles. Actuarial techniques are nowadays starting to be applied in wider fields and it is suggested that the history of actuarial science could be taught in sixth forms and universities to students of risk and finance.     

A practical synthesis of (+)-cocaine

(+)-Cocaine has been prepared from commercially available 3-tropinone in four steps. Synthetic procedures and experimental details are provided.     

The polylogarithm in the field of two irreducible quintics

A brief review of the polylogarithmic ladder and its cyclotomic equation is followed by an application to the roots of two irreducible quintic equations. The first is unique in its class and possesses four accessible and two inaccessible valid ladders. The other equation gives rise to a single ladder determinable, at the present time, only by numerical computation, and is a member of a completely new category.     

Multi-parameter evaluation of fast sol–gel process by terahertz measurements

We present a feasibility study to apply terahertz (THz) spectroscopy and THz imaging as non-destructive diagnostic tools for sol–gel analysis, manufacturing and quality control. By performing THz spectroscopy on liquid and solid samples we were able to follow several key parameters during the sol–gel formation process and of the final product. Sol–gel transformations were monitored by THz absorption, whereas density changes have been observed through changes in refractive indices. Time domain spectroscopy (TDS), both in transmission and reflection geometries, was used to monitor the properties of fast sol–gel resins. THz imaging of gold coated, thin-film sol–gel enables us to determine inhomogeneities and defects in their internal structure. We demonstrated that THz spectroscopy can be implemented as an online analytical tool for multi-parameter evaluation of the sol–gel process during fabrication, and of the final product.     

Energy cost to make a hole in the Fermi sea

The change in energy of an ideal Fermi gas when a local one-body potential is inserted into the system, or when the density is changed locally, are important quantities in condensed matter physics. We show that they can be rigorously bounded from below by a universal constant times the value given by the semiclassical approximation.     

Determination of highly polar compounds in water samples around former ammunition plants

Summary A method was developed for the determination of nitrobenzoic acids and nitrophenols as well as of diaminoaromatics and was applied to the analysis of water samples from the former ammunition plant at Elsnig (Saxony, Germany). The procedure is based on a preseparation into a neutral, an acidic and a basic fraction by multi-step extraction at different pH values followed by HPLC analysis with UV and electrochemical detectors, coupled in series. Applying optimized enrichment conditions, all investigated compounds were extracted from spiked distilled water with recoveries >80% and variation coefficients <7%. Similar results were obtained with spiked ground water samples. After enrichment, all compounds can be analysed by HPLC with UV detection at concentrations below 100 ngL⁻¹. The electrochemical detector (ELCD) allowed a selective and sensitive detection of the nitrophenols and especially of the diaminoaromatics and, therefore, provides, some advantages in the analysis of real samples. Presented at the 21^st ISC held in Stuttgart, Germany, 15^th–20^th September, 1996