360 research outputs found
Mode-selective coupling of coherent phonons to the Bi2212 electronic band structure
Cuprate superconductors host a multitude of low-energy optical phonons. Using
time- and angle-resolved photoemission spectroscopy, we study coherent phonons
in BiSrCaYCuO. Sub-meV
modulations of the electronic band structure are observed at frequencies of
and THz. For the dominant mode at 3.94 THz, the
amplitude of the band energy oscillation weakly increases as a function of
momentum away from the node. Theoretical calculations allow identifying the
observed modes as CuO-derived phonons. The Bi- and Sr-derived
modes which dominate Raman spectra in the relevant frequency range are
absent in our measurements. This highlights the mode-selectivity for phonons
coupled to the near-Fermi-level electrons, which originate from CuO
planes and dictate thermodynamic properties.Comment: 7 pages, 3 figure
How are soil use and management reflected by soil organic matter characteristics: a spectroscopic approach
We studied the quantitative and qualitative changes of soil organic matter (SOM) due to different land
uses (arable versus grassland) and treatments (organic manure and mineral fertilizer) within an agricultural crop rotation in a long-term field experiment, conducted since 1956 at Ultuna, Sweden, on a Eutric
Cambisol. The organic carbon (OC) content of the grassland plot was 1.8 times greater than that of the
similarly fertilized Ca(NO3)
2 treated cropped plots. The comparison of two dispersion techniques (a lowenergy sonication and a chemical dispersion which yield inherent soil aggregates) showed that increasing
OC contents of the silt-sized fractions were not matched by a linear increase of silt-sized aggregates. This
indicated saturation of the aggregates with OC and a limited capacity of particles to protect OC
physically. Thermogravimetric analyses suggested an increase of free organic matter with increasing
OC contents. Transmission FT-IR spectroscopy showed relative enrichment of carboxylic, aromatic,
CH and NH groups in plots with increasing OC contents. The silt-sized fractions contained the largest
SOM pool and, as revealed by 13C NMR spectroscopy, were qualitatively more influenced by the plant
residue versus manure input than the clay fractions. Alkyl and O-alkyl C in the silt-sized fractions
amounted to 57.4% of organic carbon in the animal manure treated plots and 50–53% in the other
treatments.We thank the Austrian Science Fund (Fonds zur FĂ–rderung
der wissenschaftlichen Forschung) for funding this bilateral
project.Peer reviewe
Visions of a more precise soil biology
Includes bibliographical references (pages 389-390).Soils have often been viewed as a black box. Soil biology is difficult to study with the precision we would wish, due to the presence of considerable soil heterogeneity, a huge diversity of organisms, and a plethora of interacting processes taking place in a complex physical-chemical environment. We have isolated a tiny fraction of the known organisms, and the possible interactions of soil parent materials, landscape, land use, depth and time with the biota mean that we are to some extent still fumbling in the dark. There have been great advances, but we argue that the pace of advance could be faster. To progress, science needs new theory and concepts but also acceptable methodologies. Coherent and generally accepted theoretical knowledge exists in many areas, but there is a shortage of valid and exact methods to test new and sometimes even old hypotheses. New methods add knowledge, but they also can add to the confusion if they are not tied to the existing knowledge base. We speculate on how to improve soil biology through improving the way we perform and interpret research. Can we deal with soil variability? Can we measure the critical variables with adequate precision to test our hypotheses? Can we avoid reinventing the wheel? Can we find a balance between the freedom to test new and maybe even controversial ideas and the control and direction of research required by society?
Life cycle modelling of environmental impacts of application of processed organic municipal solid waste on agricultural land (EASEWASTE)
A model capable of quantifying the potential environmental impacts of agricultural application of composted or anaerobically digested source-separated organic municipal solid waste (MSW) is presented. In addition to the direct impacts, the model accounts for savings by avoiding the production and use of commercial fertilizers. The model is part of a larger model, Environmental Assessment of Solid Waste Systems and Technology (EASEWASTE), developed as a decisionsupport model, focusing on assessment of alternative waste management options. The environmental impacts of the land application of processed organic waste are quantified by emission coefficients referring to the composition of the processed waste and related to specific crop rotation as well as soil type. The model contains several default parameters based on literature data, field experiments and modelling by the agro-ecosystem model, Daisy. All data can be modified by the user allowing application of the model to other situations. A case study including four scenarios was performed to illustrate the use of the model. One tonne of nitrogen in composted and anaerobically digested MSW was applied as fertilizer to loamy and sandy soil at a plant farm in western Denmark. Application of the processed organic waste mainly affected the environmental impact categories global warming (0.4–0.7 PE), acidification (–0.06 (saving)–1.6 PE), nutrient enrichment (–1.0 (saving)–3.1 PE), and toxicity. The main contributors to these categories were nitrous oxide formation (global warming), ammonia volatilization (acidification and nutrient enrichment), nitrate losses (nutrient enrichment and groundwater contamination), and heavy metal input to soil (toxicity potentials). The local agricultural conditions as well as the composition of the processed MSW showed large influence on the environmental impacts. A range of benefits, mainly related to improved soil quality from long-term application of the processed organic waste, could not be generally quantified with respect to the chosen life cycle assessment impact categories and were therefore not included in the model. These effects should be considered in conjunction with the results of the life cycle assessment
Persistent order due to transiently enhanced nesting in an electronically excited charge density wave
Non-equilibrium conditions may lead to novel properties of materials with
broken symmetry ground states not accessible in equilibrium as vividly
demonstrated by non-linearly driven mid-infrared active phonon excitation.
Potential energy surfaces of electronically excited states also allow to
direct nuclear motion, but relaxation of the excess energy typically excites
fluctuations leading to a reduced or even vanishing order parameter as
characterized by an electronic energy gap. Here, using femtosecond time- and
angle-resolved photoemission spectroscopy, we demonstrate a tendency towards
transient stabilization of a charge density wave after near-infrared
excitation, counteracting the suppression of order in the non-equilibrium
state. Analysis of the dynamic electronic structure reveals a remaining energy
gap in a highly excited transient state. Our observation can be explained by a
competition between fluctuations in the electronically excited state, which
tend to reduce order, and transiently enhanced Fermi surface nesting
stabilizing the order
Nitrogen and sulphur management: challenges for organic sources in temperate agricultural systems
A current global trend towards intensification or specialization of agricultural enterprises has been accompanied by increasing public awareness of associated environmental consequences. Air and water pollution from losses of nutrients, such as nitrogen (N) and sulphur (S), are a major concern. Governments have initiated extensive regulatory frameworks, including various land use policies, in an attempt to control or reduce the losses. This paper presents an overview of critical input and loss processes affecting N and S for temperate climates, and provides some background to the discussion in subsequent papers evaluating specific farming systems. Management effects on potential gaseous and leaching losses, the lack of synchrony between supply of nutrients and plant demand, and options for optimizing the efficiency of N and S use are reviewed. Integration of inorganic and organic fertilizer inputs and the equitable re-distribution of nutrients from manure are discussed. The paper concludes by highlighting a need for innovative research that is also targeted to practical approaches for reducing N and S losses, and improving the overall synchrony between supply and demand
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