9,841 research outputs found

    Angular Momentum on the Lattice: The Case of Non-Zero Linear Momentum

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    The irreducible representations (IRs) of the double cover of the Euclidean group with parity in three dimensions are subduced to the corresponding cubic space group. The reduction of these representations gives the mapping of continuum angular momentum states to the lattice in the case of non-zero linear momentum. The continuous states correspond to lattice states with the same momentum and continuum rotational quantum numbers decompose into those of the IRs of the little group of the momentum vector on the lattice. The inverse mapping indicates degeneracies that will appear between levels of different lattice IRs in the continuum limit, recovering the continuum angular momentum multiplets. An example of this inverse mapping is given for the case of the ``moving'' isotropic harmonic oscillator.Comment: v3) Little groups for lattice momenta corrected. Includes corrections from erratum submitted to Phys. Rev. D and a more consistent labeling scheme. v2) Minor changes to little groups. (9 pages

    Multiparticle States and the Hadron Spectrum on the Lattice

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    The Clebsch-Gordan decomposition is calculated for direct products of the irreducible representations of the cubic space group. These results are used to identify multiparticle states which appear in the hadron spectrum on the lattice. Consideration of the cubic space group indicates how combinations of both zero momentum and non-zero momentum multiparticle states contribute to the spectrum.Comment: v2) Little groups for lattice momenta corrected. Includes a more consistent labeling scheme. (13 pages

    Calcium carbonate, opal, and quartz in Holocene pelagic sediments and the calcite compensation level in the South Atlantic Ocean

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    Calcium carbonate is the dominant component in the pelagic sediments of the South Atlantic; its distribution pattern can be explained by use of bottom-water circulation. Biogenous opal concentrations occur in two bands, near the Equator and around 50°S; these concentrations are associated with zones of high biological productivity in surface waters...

    The Macroeconomic News Cycle and Uncertainty Resolution

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    We examine the behavior of return volatility and trading at 5-minute intervals in the treasury bond futures market in the context of the monthly macroeconomic news cycle. We advance and confirm the hypothesis that volatility and trading activity are higher in the first half of the month. The data indicate that these patterns arise from at least two sources: (1) a higher level of uncertainty regarding the value of news in announcements in the first half of the month, and (2) improvement in efficiency of macroeconomic forecasts from the first to the second half of the month

    The Macroeconomic News Cycle and Uncertainty Resolution

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    We examine the behavior of return volatility and trading at 5-minute intervals in the treasury bond futures market in the context of the monthly macroeconomic news cycle. We advance and confirm the hypothesis that volatility and trading activity are higher in the first half of the month. The data indicate that these patterns arise from at least two sources: (1) a higher level of uncertainty regarding the value of news in announcements in the first half of the month, and (2) improvement in efficiency of macroeconomic forecasts from the first to the second half of the month

    Genetic diversity of Mycobacterium tuberculosis in Peru and exploration of phylogenetic associations with drug resistance.

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    BACKGROUND: There is limited available data on the strain diversity of M tuberculosis in Peru, though there may be interesting lessons to learn from a setting where multidrug resistant TB has emerged as a major problem despite an apparently well-functioning DOTS control programme. METHODS: Spoligotyping was undertaken on 794 strains of M tuberculosis collected between 1999 and 2005 from 553 community-based patients and 241 hospital-based HIV co-infected patients with pulmonary tuberculosis in Lima, Peru. Phylogenetic and epidemiologic analyses permitted identification of clusters and exploration of spoligotype associations with drug resistance. RESULTS: Mean patient age was 31.9 years, 63% were male and 30.4% were known to be HIV+. Rifampicin mono-resistance, isoniazid mono-resistance and multidrug resistance (MDR) were identified in 4.7%, 8.7% and 17.3% of strains respectively. Of 794 strains from 794 patients there were 149 different spoligotypes. Of these there were 27 strains (3.4%) with novel, unique orphan spoligotypes. 498 strains (62.7%) were clustered in the nine most common spoligotypes: 16.4% SIT 50 (clade H3), 12.3% SIT 53 (clade T1), 8.3% SIT 33 (LAM3), 7.4% SIT 42 (LAM9), 5.5% SIT 1 (Beijing), 3.9% SIT 47 (H1), 3.0% SIT 222 (clade unknown), 3.0% SIT1355 (LAM), and 2.8% SIT 92 (X3). Amongst HIV-negative community-based TB patients no associations were seen between drug resistance and specific spoligotypes; in contrast HIV-associated MDRTB, but not isoniazid or rifampicin mono-resistance, was associated with SIT42 and SIT53 strains. CONCLUSION: Two spoligotypes were associated with MDR particularly amongst patients with HIV. The MDR-HIV association was significantly reduced after controlling for SIT42 and SIT53 status; residual confounding may explain the remaining apparent association. These data are suggestive of a prolonged, clonal, hospital-based outbreak of MDR disease amongst HIV patients but do not support a hypothesis of strain-specific propensity for the acquisition of resistance-conferring mutations

    Locations of marine animals revealed by carbon isotopes

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    Knowing the distribution of marine animals is central to understanding climatic and other environmental influences on population ecology. This information has proven difficult to gain through capture-based methods biased by capture location. Here we show that marine location can be inferred from animal tissues. As the carbon isotope composition of animal tissues varies with sea surface temperature, marine location can be identified by matching time series of carbon isotopes measured in tissues to sea surface temperature records. Applying this technique to populations of Atlantic salmon (Salmo salar L.) produces isotopically-derived maps of oceanic feeding grounds, consistent with the current understanding of salmon migrations, that additionally reveal geographic segregation in feeding grounds between individual philopatric populations and age-classes. Carbon isotope ratios can be used to identify the location of open ocean feeding grounds for any pelagic animals for which tissue archives and matching records of sea surface temperature are available
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