Simulations of a Scintillator Compton Gamma Imager for Safety and Security

We are designing an all-scintillator Compton gamma imager for use in security investigations and remediation actions involving radioactive threat material. To satisfy requirements for a rugged and portable instrument, we have chosen solid scintillator for the active volumes of both the scatter and absorber detectors. Using the BEAMnrc/EGSnrc Monte Carlo simulation package, we have constructed models using four different materials for the scatter detector: LaBr_3, NaI, CaF_2 and PVT. We have compared the detector performances using angular resolution, efficiency, and image resolution. We find that while PVT provides worse performance than that of the detectors based entirely on inorganic scintillators, all of the materials investigated for the scatter detector have the potential to provide performance adequate for our purposes.Comment: Revised text and figures, Presented at SORMA West 2008, Published in IEEE Transactions on Nuclear Scienc

Data Structure for the Use of Patterns in the Perceptual Ordering of the Game of Chess

It is well known that the way one perceives a problem can influence the difficulty of solving the problem in a profound way. In the case of computer chess playing programs, one finds that most programs perceive the game in much the same way. They are all based on Shannon\u27s original proposal for chess playing programs. His approach was to generate all of the possible combinations of moves up to a certain number of plays and then a subset of all combinations to a deeper level thereafter. Each of these moves would then be evaluated as to its relative worth. This paper lays the foundation for research in an alternate method of approaching the game based on how human experts perceive the board initially. A suitable data structure for this is then proposed and discussed

Spin Susceptibility and Gap Structure of the Fractional-Statistics Gas

This paper establishes and tests procedures which can determine the electron energy gap of the high-temperature superconductors using the $t\!-\!J$ model with spinon and holon quasiparticles obeying fractional statistics. A simpler problem with similar physics, the spin susceptibility spectrum of the spin 1/2 fractional-statistics gas, is studied. Interactions with the density oscillations of the system substantially decrease the spin gap to a value of $(0.2 \pm 0.2)$ $\hbar \omega_c$, much less than the mean-field value of $\hbar\omega_c$. The lower few Landau levels remain visible, though broadened and shifted, in the spin susceptibility. As a check of the methods, the single-particle Green's function of the non-interacting Bose gas viewed in the fermionic representation, as computed by the same approximation scheme, agrees well with the exact results. The same mechanism would reduce the gap of the $t\!-\!J$ model without eliminating it.Comment: 35 pages, written in REVTeX, 16 figures available upon request from [email protected]

The use of tobacco and related substances in ethnic minorities : the development of a culturally valid measure

Introduction. Meeting the needs of migrant groups in Europe requires cross-culturally valid questionnaires, a substantial challenge to researchers. The Rose Angina Questionnaire (RAQ) is an important measure of coronary heart disease prevalence. It consists of seven items that collectively yield a diagnosis of angina. It has been shown to perform inconsistently across some ethnic groups in Britain. This study aimed to assess the need for modifying the RAQ for cross-culturally valid use in the three main ethnic groups in Scotland.Methods. Interviews were carried out with Pakistani Punjabi speakers (n=26), Chinese Cantonese speakers (n=29) and European-origin English speakers (n=25). Bilingual project workers interviewed participants and provided translation and commentary to the English-speaking researcher. Participants were asked about general and cardiovascular health beliefs and behaviours, and about attitudes to pain and chest pain. They were also asked to comment on their understanding of an existing version of the RAQ in their language.Results. No dominant themes in the cultural construction of health, pain or cardiovascular knowledge emerged that may significantly influence RAQ response between language groups. Problems were encountered with the Punjabi and Cantonese translations of the RAQ. For example, the translation for &ldquo;chest&rdquo; was interpreted by some Pakistani and fewer Chinese women to mean &ldquo;breasts&rdquo;. &ldquo;Walking uphill&rdquo; was translated in Chinese as &ldquo;walking the hill&rdquo;, without stipulation of the direction, so that some Cantonese speakers interpreted the question as meaning walking downhill. In addition, many Chinese interpreted RAQ items to be referring to breathlessness rather than chest pain due to ambiguous wording.Conclusion. Existing Punjabi and Cantonese versions of the RAQ should be modified before being used in multi-ethnic surveys. Current versions are unlikely to be yielding data that is comparable across groups. Other language versions also require similar investigation to study the cardiovascular health of Europe&rsquo;s migrant groups.<br /

Spin Transition in Strongly Correlated Bilayer Two Dimensional Electron Systems

Using a combination of heat pulse and nuclear magnetic resonance techniques we demonstrate that the phase boundary separating the interlayer phase coherent quantum Hall effect at $\nu_T = 1$ in bilayer electron gases from the weakly coupled compressible phase depends upon the spin polarization of the nuclei in the host semiconductor crystal. Our results strongly suggest that, contrary to the usual assumption, the transition is attended by a change in the electronic spin polarization.Comment: 4 pages, 3 postscript figur

Measuring the condensate fraction of rapidly rotating trapped boson systems: off-diagonal order from the density

We demonstrate a direct connection between the density profile of a system of ultra-cold trapped bosonic particles in the rapid-rotation limit and its condensate fraction. This connection can be used to probe the crossover from condensed vortex-lattice states to uncondensed quantum fluid states that occurs in rapidly rotating boson systems as the particle density decreases or the rotation frequency increases. We illustrate our proposal with a series of examples, including ones based on models of realistic finite trap systems, and comment on its application to freely expanding boson density profile measurements.Comment: 4 pages, 3 figures, version accepted for publication in Phys. Rev. Let

Spectral and stratigraphic mapping of hydrated sulfate and phyllosilicate-bearing deposits in northern Sinus Meridiani, Mars

We present detailed stratigraphic and spectral analyses that focus on a region in northern Sinus Meridiani located between 1°N to 5°N latitude and 3°W to 1°E longitude. Several stratigraphically distinct units are defined and mapped using morphologic expression, spectral properties, and superposition relationships. Previously unreported exposures of hydrated sulfates and Fe/Mg smectites are identified using MRO CRISM and MEX OMEGA near‐infrared (1.0 to 2.5 µm) spectral reflectance observations. Layered deposits with monohydrated and polyhydrated sulfate spectral signatures that occur in association with a northeast‐southwest trending valley are reexamined using highresolution CRISM, HiRISE, and CTX images. Layers that are spectrally dominated by monohydrated and polyhydrated sulfates are intercalated. The observed compositional layering implies that multiple wetting events, brine recharge, or fluctuations in evaporation rate occurred. We infer that these hydrated sulfate‐bearing layers were unconformably deposited following the extensive erosion of preexisting layered sedimentary rocks and may postdate the formation of the sulfate‐ and hematite‐bearing unit analyzed by the MER Opportunity rover. Therefore, at least two episodes of deposition separated by an unconformity occurred. Fe/Mg phyllosilicates are detected in units that predate the sulfateand hematite‐bearing unit. The presence of Fe/Mg smectite in older units indicates that the relatively low pH formation conditions inferred for the younger sulfate‐ and hematitebearing unit are not representative of the aqueous geochemical environment that prevailed during the formation and alteration of earlier materials. Sedimentary deposits indicative of a complex aqueous history that evolved over time are preserved in Sinus Meridiani, Mars