4,589 research outputs found
The global technical potential of bio-energy in 2050 considering sustainability constraints
Bio-energy, that is, energy produced from organic non-fossil material of biological origin, is promoted as a substitute for non-renewable (e.g., fossil) energy to reduce greenhouse gas (GHG) emissions and dependency on energy imports. At present, global bio-energy use amounts to approximately 50 EJ/yr, about 10% of humanity's primary energy supply. We here review recent literature on the amount of bio-energy that could be supplied globally in 2050, given current expectations on technology, food demand and environmental targets ('technical potential'). Recent studies span a large range of global bio-energy potentials from ≈30 to over 1000 EJ/yr. In our opinion, the high end of the range is implausible because of (1) overestimation of the area available for bio-energy crops due to insufficient consideration of constraints (e.g., area for food, feed or nature conservation) and (2) too high yield expectations resulting from extrapolation of plot-based studies to large, less productive areas. According to this review, the global technical primary bio-energy potential in 2050 is in the range of 160-270 EJ/yr if sustainability criteria are considered. The potential of bio-energy crops is at the lower end of previously published ranges, while residues from food production and forestry could provide significant amounts of energy based on an integrated optimization ('cascade utilization') of biomass flows. © 2010 Elsevier B.V
Doubly heavy spin--1/2 baryon spectrum in QCD
We calculate the mass and residue of the heavy spin--1/2 baryons containing
two heavy b or c quarks in the framework of QCD sum rules. We use the most
general form of the interpolating current in its symmetric and anti-symmetric
forms with respect to the exchange of heavy quarks, to calculate the two-point
correlation functions describing the baryons under consideration. A comparison
of the obtained results with existing predictions from various approaches is
also made.Comment: 17 Pages, 2 Figures and 2 Table
Teaming Models with Intelligent Systems at the Workplace
Die Wirtschaftsinformatik (WI) hat sich einen festen Platz in den deutschsprachigen Hochschulen gesichert. Mit wachsendem Fachkräftemangel dürften ihre Beiträge zur Ausbildung von Fachleuten für automatische Systeme und zur diesbezüglichen Forschung noch wichtiger werden. In der Öffentlichkeit und z. T. auch in den Fachmedien entspricht ihr Bekanntheitsgrad nicht ihrer gesellschaftlichen Bedeutung. Beispielsweise werden von relativen Laien, z. B. in der Politik, traditionelle Gegenstände des Faches als Neuentwicklung dargestellt. Wir plädieren dafür, dass sich die WI mehr als bisher nicht nur als interdisziplinäres Fach zwischen BWL und Informatik begreift, sondern verstärkt auch auf Grenzgebieten wie Öffentlicher Verwaltung, Politik und Recht arbeitet. Wege dazu sind u. a. Übertragung von IT-Lösungen aus der Privatwirtschaft in die Öffentliche Verwaltung, Warnungen vor Übertreibung und Moden oder differenzierte Identifikation von Vor- und Nachteilen neuer Methoden im Vergleich zu bekannten. Im akademischen Umfeld ist zu hinterfragen, ob die aktuellen Anreizsysteme für Wissenschaftlerinnen und Wissenschaftler förderlich sind
A Simple Grand Unified Relation between Neutrino Mixing and Quark Mixing
It is proposed that all flavor mixing is caused by the mixing of the three
quark and lepton families with vectorlike fermions in 5 + 5-bar multiplets of
SU(5). This simple assumption implies that both V_{CKM} and U_{MNS} are
generated by a single matrix. The entire 3-by-3 complex mass matrix of the
neutrinos M_{nu} is then found to have a simple expression in terms of two
complex parameters and an overall scale. Thus, all the presently unknown
neutrino parameters are predicted. The best fits are for theta_{atm} less than
or approximately 40 degrees. The leptonic Dirac CP phase is found to be
somewhat greater than pi radians.Comment: 10 pages, 4 figures, one table. Typos correcte
Land use change and the impact on greenhouse gas exchange in north Australian savanna soils
Savanna ecosystems are subjected to accelerating land use change as human
demand for food and forest products increases. Land use change has been
shown to both increase and decrease greenhouse gas fluxes from savannas and
considerable uncertainty exists about the non-CO<sub>2</sub> fluxes from the soil.
We measured methane (CH<sub>4</sub>), nitrous oxide (N<sub>2</sub>O) and carbon dioxide
(CO<sub>2</sub>) over a complete wet-dry seasonal cycle at three replicate sites
of each of three land uses: savanna, young pasture and old pasture
(converted from savanna 5–7 and 25–30 yr ago, respectively) in the
Douglas Daly region of Northern Australia. The effect of break of season
rains at the end of the dry season was investigated with two irrigation
experiments.
Land use change from savanna to pasture increased net greenhouse gas fluxes
from the soil. Pasture sites were a weaker sink for CH<sub>4</sub> than savanna
sites and, under wet conditions, old pastures turned from being sinks to a
significant source of CH<sub>4</sub>. Nitrous oxide emissions were generally very
low, in the range of 0 to 5 μg N<sub>2</sub>O-N m<sup>−2</sup> h<sup>−1</sup>, and under
dry conditions soil uptake of N<sub>2</sub>O was apparent. Break of season rains
produced a small, short lived pulse of N<sub>2</sub>O up to 20 μg N<sub>2</sub>O-N m<sup>−2</sup> h<sup>−1</sup>, most evident in pasture soil. Annual cumulative soil
CO<sub>2</sub> fluxes increased after clearing, with savanna (14.6 t CO<sub>2</sub>-C ha<sup>−1</sup> yr<sup>−1</sup>) having the lowest fluxes compared to old pasture
(18.5 t CO<sub>2</sub>-C ha<sup>−1</sup> yr<sup>−1</sup>) and young pasture (20.0 t CO<sub>2</sub>-C ha<sup>−1</sup> yr<sup>−1</sup>). Clearing savanna increased soil-based greenhouse gas
emissions from 53 to ∼ 70 t CO<sub>2</sub>-equivalents, a 30% increase
dominated by an increase in soil CO<sub>2</sub> emissions and shift from soil
CH<sub>4</sub> sink to source. Seasonal variation was clearly driven by soil water
content, supporting the emerging view that soil water content is a more
important driver of soil gas fluxes than soil temperature in tropical
ecosystems where temperature varies little among seasons
An Exploration of the Antecedents to Effective Recommender System Message Design
Recommender Systems (RS) aim to improve users’ decision quality and reduce decision-related effort. Prior research has focused on the impact of the entire system on recommendation acceptance and system use intentions, while largely overlooking the role of message design.
To fill this void, a systematic literature review was undertaken to answer three research questions: (i) What comprises the current knowledge base of antecedents to effective RS message design? (ii) What significant results from past research can inform current scholars and practitioners of optimal RS message design practices? (iii) What are opportunities for future research in revealing guidelines for optimizing RS message design
Constrained analytical interrelations in neutrino mixing
Hermitian squared mass matrices of charged leptons and light neutrinos in the
flavor basis are studied under general additive lowest order perturbations away
from the tribimaximal (TBM) limit in which a weak basis with mass diagonal
charged leptons is chosen. Simple analytical expressions are found for the
three measurable TBM-deviants in terms of perturbation parameters appearing in
the neutrino and charged lepton eigenstates in the flavor basis. Taking
unnatural cancellations to be absent and charged lepton perturbation parameters
to be small, interrelations are derived among masses, mixing angles and the
amount of CP-violation.Comment: To be published in the Springer Proceedings in the Physics Series
under the heading of the XXI DAE-BRNS Symposium (Guwahati, India
MODIS vegetation products as proxies of photosynthetic potential along a gradient of meteorologically and biologically driven ecosystem productivity
© 2016 Author(s). A direct relationship between gross ecosystem productivity (GEP) estimated by the eddy covariance (EC) method and Moderate Resolution Imaging Spectroradiometer (MODIS) vegetation indices (VIs) has been observed in many temperate and tropical ecosystems. However, in Australian evergreen forests, and particularly sclerophyll and temperate woodlands, MODIS VIs do not capture seasonality of GEP. In this study, we re-evaluate the connection between satellite and flux tower data at four contrasting Australian ecosystems, through comparisons of GEP and four measures of photosynthetic potential, derived via parameterization of the light response curve: ecosystem light use efficiency (LUE), photosynthetic capacity (Pc), GEP at saturation (GEPsat), and quantum yield (α) with MODIS vegetation satellite products, including VIs, gross primary productivity (GPPMOD) leaf area index (LAIMOD), and fraction of photosynthetic active radiation (fPARMOD). We found that satellite-derived biophysical products constitute a measurement of ecosystem structure (e.g. leaf area index-quantity of leaves) and function (e.g. leaf level photosynthetic assimilation capacity-quality of leaves), rather than GEP. Our results show that in primarily meteorological-driven (e.g. photosynthetic active radiation, air temperature, and/or precipitation) and relatively aseasonal ecosystems (e.g. evergreen wet sclerophyll forests), there were no statistically significant relationships between GEP and satellite-derived measures of greenness. In contrast, for phenology-driven ecosystems (e.g. tropical savannas), changes in the vegetation status drove GEP, and tower-based measurements of photosynthetic activity were best represented by VIs. We observed the highest correlations between MODIS products and GEP in locations where key meteorological variables and vegetation phenology were synchronous (e.g. semi-arid Acacia woodlands) and low correlation at locations where they were asynchronous (e.g. Mediterranean ecosystems). However, we found a statistical significant relationship between the seasonal measures of photosynthetic potential (Pc and LUE) and VIs, where each ecosystem aligns along a continuum; we emphasize here that knowledge of the conditions in which flux tower measurements and VIs or other remote sensing products converge greatly advances our understanding of the mechanisms driving the carbon cycle (phenology and climate drivers) and provides an ecological basis for interpretation of satellite-derived measures of greenness
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