6,207 research outputs found
Anaerobic Digestion of Wastewater-Grown Algae Biomass With Optimized Biogas Yields and Nutrient Solubilzation
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
We consider source-free electromagnetic fields in spacetimes possessing a
non-null Killing vector field, . We assume further that the
electromagnetic field tensor, , is invariant under the action of the
isometry group induced by . 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
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
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
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
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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