Description: Gamma-ray imaging utilizing Compton scattering has traditionally relied on measuring coincident gamma-ray interactions to map directional information of the source distribution. This coincidence requirement makes it an inherently inefficient process. We present an approach to gamma-ray reconstruction from Compton scattering that requires only a single electron tracking detector, thus removing the coincidence requirement. From the Compton scattered electron momentum distribution, our algorithm analytically computes the incident photon's correlated direction and energy distributions. Because this method maps the source energy and location, it is useful in applications, where prior information about the source distribution is unknown. We demonstrate this method with electron tracks measured in a scientific Si charge coupled device. While this method was demonstrated with electron tracks in a Si-based detector, it is applicable to any detector that can measure electron direction and energy, or equivalently the electron momentum. For example, it can increase the sensitivity to obtain energy and direction in gas-based systems that suffer from limited efficiency.

Description: tFatty acids of microalgae have been studied as potential chemotaxonomic markers, to reveal plausi-ble lipid phycotoxins or in the context of mass production of algal biofuels. The planctonic microalgaeAlexandrium tamarense (Dinophyceae) is a common harmful algal bloom species that often proliferatesin eutrophic costal waters. Alexandrium blooms are the proximal source of toxins associated with par-alytic shellfish poisoning (PSP), a neurological affliction that has caused human illness for centuries viaconsumption of contaminated shellfish. However, data on the fatty acid composition of A. tamarense iscurrently limited. For this reason, we cultivated a well-defined strain of A. tamarense (Alex2, group I, NorthAmerican clade) in order to study both its major and minor fatty acids. The harvested microalgae weretransesterified and the fatty acid methyl esters were fractionated by means of high-speed counter-currentchromatography (HSCCC). The resulting 31 HSCCC fractions were analyzed by gas chromatography withmass spectrometry (GC/MS). Unknown substances were identified by transferring assorted HSCCC frac-tions into picolinyl or pyrrolidide derivatives. Twenty fatty acids (range 0.2–22.9% contribution to totalfatty acids) were identified in the unfractionated sample with 14:0, 16:0, 18:1n-9, 18:4n-3, 18:5n-3 and22:6n-3 representing 〉 80% of the total fatty acids. HSCCC fractionation enabled the identification of fur-ther 22 trace fatty acids contributing between ∼0.01 and 0.2% to total fatty acids. The fatty acids includedseveral branched-chain fatty acids as well as scarcely reported fatty acids like 11-methyl-18:1n-6tr or18:2�4,9. In order to enable a better comparability and repeatability of HSCCC fractionations, we calcu-lated for each HSCCC fraction the total volume of mobile phase, which had passed the HSCCC. From thisvolume we subtracted the volume of extruded stationary phase and divided the corrected volume by thetotal coil volume. These elution values were in good agreement with the partition ratios of randomlychosen fatty acid methyl esters obtained in shake flask tests, which allows the prediction of the elutionfrom the HSCCC system when the partition ratio is known.