760 research outputs found
How tight are the limits to land and water use? - Combined impacts of food demand and climate change
In the coming decades, world agricultural systems will face serious transitions. Population growth, income and lifestyle changes will lead to considerable increases in food demand. Moreover, a rising demand for renewable energy and biodiversity protection may restrict the area available for food production. On the other hand, global climate change will affect production conditions, for better or worse depending on regional conditions. In order to simulate these combined effects consistently and in a spatially explicit way, we have linked the Lund-Potsdam-Jena Dynamic Global Vegetation Model (LPJ) with a "Management model of Agricultural Production and its Impact on the Environment" (MAgPIE). LPJ represents the global biosphere with a spatial resolution of 0.5 degree. MAgPIE covers the most important agricultural crop and livestock production types. A prototype has been developed for one sample region. In the next stage this will be expanded to several economically relevant regions on a global scale, including international trade. The two models are coupled through a layer of productivity zones. In the paper we present the modelling approach, develop first joint scenarios and discuss selected results from the coupled modelling system
Ramanujan sums for signal processing of low frequency noise
An aperiodic (low frequency) spectrum may originate from the error term in
the mean value of an arithmetical function such as M\"obius function or
Mangoldt function, which are coding sequences for prime numbers. In the
discrete Fourier transform the analyzing wave is periodic and not well suited
to represent the low frequency regime. In place we introduce a new signal
processing tool based on the Ramanujan sums c_q(n), well adapted to the
analysis of arithmetical sequences with many resonances p/q. The sums are
quasi-periodic versus the time n of the resonance and aperiodic versus the
order q of the resonance. New results arise from the use of this
Ramanujan-Fourier transform (RFT) in the context of arithmetical and
experimental signalsComment: 11 pages in IOP style, 14 figures, 2 tables, 16 reference
Mechanical Strength Degradation of Graphite Fiber Reinforced Thermoset Composites Due to Porosity
The mechanical strength of composite laminates is sensitive to the presence of porosity. Porosity in laminates is generally considered to be a random distribution of voids incurred during the manufacture process. Larger, interlaminar voids typically result from trapped air or moisture; smaller, intralaminar voids may occur between fibers due to improper wetting or the release of volatile gases during the cure cycle. Porosity has its greatest effects on matrix-dominated mechanical properties such as compressive strength, transverse tensile strength and interlaminar shear strength (ILSS). Judd and Wright [1] have surveyed the existing data and made an appraisal of the effects of voids on the mechanical properties of composites. In a study of porosity in filament wound/CVD carbon-carbon composite [2], the transverse tensile strength was found to decrease exponentially with increasing porosity and followed an empirical equation often attributed to Ryshkewitch [3] and Duckworth [4]: Ï = ÏmaxeBP (1) where Ïmax is the strength at zero porosity, P is the volume fraction of porosity, and B (a negative number) is an empirical constant that depends on pore size, shape, and orientation. More recently Yoshida et. al
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How tight are the limits to land and water use? - Combined impacts of food demand and climate change
In the coming decades, world agricultural systems will face serious transitions. Population growth, income and lifestyle changes will lead to considerable increases in food demand. Moreover, a rising demand for renewable energy and biodiversity protection may restrict the area available for food production. On the other hand, global climate change will affect production conditions, for better or worse depending on regional conditions. In order to simulate these combined effects consistently and in a spatially explicit way, we have linked the Lund-Potsdam-Jena Dynamic Global Vegetation Model (LPJ) with a "Management model of Agricultural Production and its Impact on the Environment" (MAgPIE). LPJ represents the global biosphere with a spatial resolution of 0.5 degree. MAgPIE covers the most important agricultural crop and livestock production types. A prototype has been developed for one sample region. In the next stage this will be expanded to several economically relevant regions on a global scale, including international trade. The two models are coupled through a layer of productivity zones. In the paper we present the modelling approach, develop first joint scenarios and discuss selected results from the coupled modelling system
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Biogeochemical potential of biomass pyrolysis systems for limiting global warming to 1.5â°C
Negative emission (NE) technologies are recognized to play an increasingly relevant role in strategies limiting mean global warming to 1.5â°C as specified in the Paris Agreement. The potentially significant contribution of pyrogenic carbon capture and storage (PyCCS) is, however, highly underrepresented in the discussion. In this study, we conduct the first quantitative assessment of the global potential of PyCCS as a NE technology based on biomass plantations. Using a process-based biosphere model, we calculate the land use change required to reach specific climate mitigation goals while observing biodiversity protection guardrails. We consider NE targets of 100â300âGtC following socioeconomic pathways consistent with a mean global warming of 1.5â°C as well as the option of additional carbon balancing required in case of failure or delay of decarbonization measures. The technological opportunities of PyCCS are represented by three tracks accounting for the sequestration of different pyrolysis products: biochar (as soil amendment), bio-oil (pumped into geological storages) and permanent-pyrogas (capture and storage of CO2 from gas combustion). In addition, we analyse how the gain in land induced by biochar-mediated yield increases on tropical cropland may reduce the pressure on land. Our results show that meeting the 1.5â°C goal through mitigation strategies including large-scale NE with plantation-based PyCCS may require conversion of natural vegetation to biomass plantations in the order of 133â3280 Mha globally, depending on the applied technology and the NE demand. Advancing towards additional bio-oil sequestration reduces land demand considerably by potentially up to 60%, while the benefits from yield increases account for another 3%â38% reduction (equalling 82â362 Mha). However, when mitigation commitments are increased by high balancing claims, even the most advanced PyCCS technologies and biochar-mediated co-benefits cannot compensate for delayed action towards phasing-out fossil fuels
Excitated state properties of 20-chloro-chlorophyll a
The excited-state and lasing properties of 20-chloro-chlorophyll a in ether solution were compared to those of chlorophyll a. Desactivation parameters and cross-sections were obtained from non-linear absorption spectroscopy in combination with a physico-mathematical methods package. The Cl substituent at C-20 (1) increases both intersystem crossing and internal conversion, (2) produces a blue-shift of the S1 absorption spectrum, and (3) leads to pronounced photochemistry
Health expenditure of employees versus self-employed individuals; a 5-year study.
It is unclear to what extent selfâemployed choose to become selfâemployed.
This study aimed to compare the health care expendituresâas a proxy for
healthâof selfâemployed individuals in the year before they started their
business, to that of employees. Differences by sex, age, and industry were
studied. In total, 5,741,457 individuals aged 25â65 years who were listed in the
tax data between 2010 and 2015 with data on their health insurance claims
were included. Selfâemployed and employees were stratified according to sex,
age, household position, personal income, region, and industry for each of the
years covered. Weighted linear regression was used to compare health care
expenditures in the preceding (year xâ1) between selfâemployed and employees (in year x). Compare
FAST CARS: Engineering a Laser Spectroscopic Technique for Rapid Identification of Bacterial Spores
Airborne contaminants, e.g., bacterial spores, are usually analyzed by time
consuming microscopic, chemical and biological assays. Current research into
real time laser spectroscopic detectors of such contaminants is based on e.g.
resonant Raman spectroscopy. The present approach derives from recent
experiments in which atoms and molecules are prepared by one (or more) coherent
laser(s) and probed by another set of lasers. The connection with previous
studies based on "Coherent Anti-Stokes Raman Spectroscopy" (CARS) is to be
noted. However generating and utilizing maximally coherent oscillation in
macromolecules having an enormous number of degrees of freedom is much more
challenging. This extension of the CARS technique is called FAST CARS
(Femtosecond Adaptive Spectroscopic Techniques for Coherent Anti-Stokes Raman
Spectroscopy), and the present paper proposes and analyses ways in which it
could be used to rapidly identify pre-selected molecules in real time.Comment: 43 pages, 21 figures; replacement with references added. Submitted to
the Proceedings of National Academy of Science
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