6,108 research outputs found

    Anaerobic Digestion of Wastewater-Grown Algae Biomass With Optimized Biogas Yields and Nutrient Solubilzation

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    Whole-cell algae biomass grown on nutrient-rich wastewater can be anaerobically digested to produce renewable heat and power, and to solubilize nutrients to grow additional algae biomass in a biorefinery system. In this study, algae biomass was grown on clarified primary wastewater in 33-m2 ponds at a 4-day residence time with sedimentation harvesting of the biomass. Lab digesters were used to test biogas yields and nutrient solubilization from the anaerobic digestion of algal biomass with and without mixing and with sonication as a pretreatment. Additionally, algae were fed to unheated and unmixed 1135-L pilot digesters to determine the effects of seasonal temperatures and organic loading rates on biogas yields and nutrient solubilization. Finally a scalability experiment was conducted to determine how well lab digesters replicated the nutrient solubilization and biogas yields of pilot digesters when they were operated at the same average daily temperature, and organic load. Overall, the tested conditions included mixing, temperature, feed pretreatment by sonication, scale, and organic loading. It was determined that unmixed, 20˚C digesters fed an average variable organic loading of 0.12 g VS/L-day had the highest yield of 0.3 L CH4/g VS fed. Compared to similarly operated digesters (30˚C, constant organic load 0.25 g VS/L-day) sonicated feed increased the mass yield of methane by 18% (0.28 L CH4/g VSintroduced), and mixing increased the mass yield of methane by 4% (0.25 L CH4/g VS). For the same digesters, sonicated feed increased the average nitrogen and phosphorus solubilization 10% and 11% with 36% N and 28% particulate P remaining, respectively. Eliminating mixing increased the average nitrogen and phosphorus solubilization by 13% and 27%, with 40% and 31% remaining as particulates, respectively. The pilot digesters produced an overall average mass yield of 0.19 L CH4/g VS, with a summer average of 0.46 L CH4/g VS and a winter average of 0.15 L CH4/g VS. For the pilot digesters, the average amount of remaining particulate nitrogen and phosphorus was 36% and 39%, respectively, with an average of 57% volatile solids destruction. Finally for the scale experiment, the pilot digesters exhibited mass and volumetric yields of 47% and 28% (0.19 L CH4/g VS; 0.011 L CH4/L-d) greater than the lab digesters. Additionally, the pilot digesters had 2% greater nitrogen solubilization and 29% less phosphorus solubilization with 23% N and 15% P, than the lab digesters. Based on these results, for a low organic load (0.01 – 0.65 g VS/L-day), it is recommended that digesters be unmixed and heated which, and have a longer winter residence time. In addition to benefiting methane yield and nutrient solubilization, these digester operating conditions would allow increased supply of nutrients to ponds during the most productive months when nutrients are being consumed at faster rates in the algae ponds

    Maxwell Fields in Spacetimes Admitting Non-Null Killing Vectors

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    We consider source-free electromagnetic fields in spacetimes possessing a non-null Killing vector field, Îľa\xi^a. We assume further that the electromagnetic field tensor, FabF_{ab}, is invariant under the action of the isometry group induced by Îľa\xi^a. It is proved that whenever the two potentials associated with the electromagnetic field are functionally independent the entire content of Maxwell's equations is equivalent to the relation \n^aT_{ab}=0. Since this relation is implied by Einstein's equation we argue that it is enough to solve merely Einstein's equation for these electrovac spacetimes because the relevant equations of motion will be satisfied automatically. It is also shown that for the exceptional case of functionally related potentials \n^aT_{ab}=0 implies along with one of the relevant equations of motion that the complementary equation concerning the electromagnetic field is satisfied.Comment: 7 pages,PACS numbers: 04.20.Cv, 04.20.Me, 04.40.+

    Hairy Black Holes, Horizon Mass and Solitons

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    Properties of the horizon mass of hairy black holes are discussed with emphasis on certain subtle and initially unexpected features. A key property suggests that hairy black holes may be regarded as `bound states' of ordinary black holes without hair and colored solitons. This model is then used to predict the qualitative behavior of the horizon properties of hairy black holes, to provide a physical `explanation' of their instability and to put qualitative constraints on the end point configurations that result from this instability. The available numerical calculations support these predictions. Furthermore, the physical arguments are robust and should be applicable also in more complicated situations where detailed numerical work is yet to be carried out.Comment: 25 pages, 5 (new) figures. Revtex file. Final version to appear in CQ

    Differences in attitudes towards/beliefs on complementary and alternative medicine witnessed between physiotherapists, nurses/paramedics and physicians

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    Background: The change in social order that took place in Croatia in the 1990s made medical pluralism - in terms of coexistence of various treatment options apparent. In spite of the European Commission and WHO recommendations, complementary and alternative medicine (CAM) failed to be regulated by the law, even upon EU accession.Materials and Methods: This study aimed at investigating the attitudes of healthcare professionals towards CAM, as well as possible differences in attitudes expressed by physicians, nurses/paramedics and physiotherapists and comprised a total of 325 healthcare professionals affiliated with either private or public healthcare facilities and belonging to one of the three major categories of healthcare providers under study. The study was carried out throughout 2011 - 2012, and made use of IMAQ (Integrative Medicine Attitude Questionnaire).Results: A total score seen in the physicians’ arm was statistically lower (M 91.76) when compared to that obtained in the nurses/paramedics’ (M 97.28) and the physiotherapists’ arm (M 97.27). Significant differences in CAM-related attitudes were proven to exist between physicians and nurses/physiotherapists (F=7.853921, p=0.000), but not between nurses and physiotherapists (δ=1.531, p=1.000). These differences boil down to higher criticism expressed by physicians as regards CAM efficiency, especially the therapeutic value of spiritual & intuitive curing methods and osteopathic & laying-on-hands treatments, while significant differences in attitudes towards acupuncture, chiropractic and massage failed to be found. Differences in healthcare professionals’ attitudes arising on the grounds of gender (T=-1.411, p=0.159), educational background (F=2.372303, p=0.095) and the number of years in service (F=0.833, p=0.436), failed to be seen as well.Conclusion: Despite the fairly high IMAQ score obtained in the study sample that speaks in favour of a positive rather than neutral CAM-related attitude of healthcare providers under study, the very structure of the IMAQ tool prevents us from the unbiased conclusion that Croatian healthcare providers support CAM. Physicians are far less prone to support alternative and spiritual treatment practices than nurses/paramedics and physiotherapists.Keywords: attitudes towards CAM; physicians, nurses/paramedics, physiotherapists, IMA

    Mechanics of multidimensional isolated horizons

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    Recently a multidimensional generalization of Isolated Horizon framework has been proposed by Lewandowski and Pawlowski (gr-qc/0410146). Therein the geometric description was easily generalized to higher dimensions and the structure of the constraints induced by the Einstein equations was analyzed. In particular, the geometric version of the zeroth law of the black hole thermodynamics was proved. In this work we show how the IH mechanics can be formulated in a dimension--independent fashion and derive the first law of BH thermodynamics for arbitrary dimensional IH. We also propose a definition of energy for non--rotating horizons.Comment: 25 pages, 4 figures (eps), last sections revised, acknowledgements and a section about the gauge invariance of introduced quantities added; typos corrected, footnote 4 on page 9 adde

    Quasi-local rotating black holes in higher dimension: geometry

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    With a help of a generalized Raychaudhuri equation non-expanding null surfaces are studied in arbitrarily dimensional case. The definition and basic properties of non-expanding and isolated horizons known in the literature in the 4 and 3 dimensional cases are generalized. A local description of horizon's geometry is provided. The Zeroth Law of black hole thermodynamics is derived. The constraints have a similar structure to that of the 4 dimensional spacetime case. The geometry of a vacuum isolated horizon is determined by the induced metric and the rotation 1-form potential, local generalizations of the area and the angular momentum typically used in the stationary black hole solutions case.Comment: 32 pages, RevTex
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