The decay of 91 min As

The energies and relative intensities of γ-rays following the β-decay of ⁷⁸As (and ⁷⁶As) to levels in ⁷⁸Se (and ⁷⁶Se) have been measured using an 8 cm³ Ge(Li) spectrometer. The β-decay of ⁷⁸As has been measured using a superconducting magnet beta-ray spectrometer with two 3 mm thick Si(Li) detectors. These data plus β-γ and γ-γ coincidence results have been used to construct a level scheme with 18 excited levels in ⁷⁸Se. The half-life of ⁷⁸As was measured to be 90.7±0.2 min.     

Enhanced stimulated Raman scattering in slow-light photonic crystal waveguides

We investigate for the first time, to our knowledge, the enhancement of the stimulated Raman scattering in slow-light silicon-on-insulator (SOI) photonic crystal line defect waveguides. By applying the Bloch-Floquet formalism to the guided modes in a planar photonic crystal, we develop a formalism that relates the intensity of the downshifted Stokes signal to the pump intensity and the modal group velocities. The formalism is then applied to two prospective schemes for enhanced stimulated Raman generation in slow-light photonic crystal waveguides. The results demonstrate a maximum factor of 104(66,000) enhancement with respect to SOI channel waveguides.     

Interference of homonuclear decoupling and exchange in the solid-state NMR of perfluorocyclohexane

We observe an interference between RF irradiation used for homonuclear decoupling of 19F and conformational exchange in the 13C spectrum of perfluorocyclohexane. We show that these effects can be readily reproduced in simulation, and characterise their dependence on the various NMR and experimental parameters. Their application to observing exchange rates on the kHz timescale is evaluated with respect to T(1rho) measurements and the connections between the two approaches established. The implications for experiments that use homonuclear decoupling of 1H to resolve 1J(CH)couplings in the solid-state are also evaluated in detail.     

A wavelet,fourier, and PCA data analysis pipeline: application to distinguishing mixtures of liquids

Using a new optical engineering technique for the "fingerprinting" of beverages and other liquids, we study and evaluate a range of features. The features are based on resolution scale, invariant frequency information, entropy, and energy. They allow mixtures of beverages to be very precisely placed in principal component plots used for the data analysis. To show this we make use of data sets resulting from optical/near-infrared and ultrasound sensors. Our liquid "fingerprinting" is a relatively open analysis framework in order to cater for different practical applications, in particular, on one hand, discrimination and best fit between fingerprints, and, on the other hand, more exploratory and open-ended data mining.     

Millimeter-wave atmospheric turbulence measurements: Instrumentation, selected results, and system effects

Increasing interest in and greater usage of the millimeter-wave frequency bands has resulted in a need for better characterization of atmospheric effects at these frequencies. While attenuation is recognized as the most significant effect, recent measurements of fluctuations in intensity and phase caused by atmospheric turbulence have shown that these phenomena will also degrade system performance at both millimeter-wave and microwave frequencies. This paper describes the millimeter-wave and meteorological instrumentation used to make these measurements and gives selected results. It is determined that phase fluctuations as great as 1.5 radians and intensity fluctuations as large as 2.8 dB are observed over a 1370 m path in hot, humid weather. The effects of these fluctuations on the performance of practical, existing microwave phased array and monopulse systems are assessed. It is determined that phase fluctuations in particular will degrade the performance of microwave adaptive nulling arrays and monopulse trackers. Intergovernmental Personnel Act appointee from the Georgia Institute of Technology supported by the University Resident Research Program of the Air Force Office of Scientific Research.     

Activation analysis with standards containing two or more active nuclides A computerized method of calculation involving decay and gamma spectral resolution

The resolution of the gamma spectra of activities induced in materials by fast neutron, charged particle and gamma photon activation is complicated by the fact that many elements produce more than one active nuclide in significant amounts. Direct resolution by least-squares fitting of the spectra of standards is only possible in these circumstances if the standard and sample spectra are obtained at the same time after irradiation, as the shapes of the standard spectra change with time. An alternative to the practical collection of spectra in this way is the correction of the standard spectra to the mid-time of counting of a sample spectrum. This may be achieved by recording spectra for a standard at different times and resolving the decay curves obtained for each channel on the basis of the half-lives of the component nuclides, which may be decay-independent or related or both. From the component nuclide count-rates in each channel at some arbitrary time, the standard spectrum at the time of counting of the sample can be generated and then used in a conventional least squares-fit of the sample spectrum. A FORTRAN IV program has been written to carry out this type of calculation on an IBM 360 65 computer. The feasibility of using this method is demonstrated by its application to activation analyses involving standards containing decay-related and independent nuclides.     

Development of an ultra-performance liquid chromatography-mass spectrometry method for the detection of lipophilic marine toxins

A rapid method for the detection of marine toxins was developed using an ultra-performance liquid chromatography (UPLC) system coupled to a latest generation mass spectrometry (MS) system. The analysis of 21 lipophilic marine toxins was achieved on an Acquity C18 column using a water-acetonitrile gradient with a cycle time of 6.6 min, reducing analysis time by more than a factor two compared to HPLC while maintaining peak resolution. Linear ranges, limits of detection and limits of quantification were established for okadaic acid (OA), pectenotoxin-2, azaspiracid-1 (AZA1), yessotoxin, gymnodimine and 13-desmethylspirolide C. The method was found to be accurate when using a triplicate methanolic extraction. Matrix effects were assessed by standard addition of OA and AZA1 in extracts of raw and heat-treated flesh of mussels and oysters. For the analysis of AZA1, the UPLC-MS method was always prone to signal suppression, while for OA analysis signal suppression was observed in extracts of raw shellfish flesh and signal enhancement in extracts of heat-treated flesh. Matrix effects occurring in the method presented are diminished compared to previous studies.