492 research outputs found
Bewirtschaftungseffekte auf Wurzelbiomasse und Kohlenstoff-Rhizodeposition von Mais in zwei Schweizer Langzeitversuchen
Below ground carbon (BGC) inputs by agricultural plants into the soil are an important variable in soil carbon (C) modelling. The sources for BGC inputs are dead root biomass and C release by living roots (C rhizodeposition). Since management effects on BGC inputs are not profoundly understood, we address the following research questions in this research project: (i) What are the proportions of root biomass and C rhizodeposition of the total BGC input in the topsoil and subsoil under maize cultivation at different sites? (ii) Does long-term fertilization practice affect total root biomass, root distribution, shoot/root ratios, and C rhizodeposition of maize? Results obtained from field experiments in 2013 on two Swiss long-term experimental sites (âDOKâ near Basel and âZOFEâ in Zurich) reveal no significant differences between total root biomasses and total C rhizodeposition of maize in different management treatments. While the proportion of topsoil (0-0.25 m) root biomass of the total (0-0.75 m) root biomass increases on the âDOKâ site, the below ground/above ground C ratios decrease on both sites with increasing management intensity (trends only)
Molecular states in carbon nanotube double quantum dots
We report electrical transport measurements through a semiconducting
single-walled carbon nanotube (SWNT) with three additional top-gates. At low
temperatures the system acts as a double quantum dot with large inter-dot
tunnel coupling allowing for the observation of tunnel-coupled molecular states
extending over the whole double-dot system. We precisely extract the tunnel
coupling and identify the molecular states by the sequential-tunneling line
shape of the resonances in differential conductance.Comment: 5 pages, 4 figure
Integrable theory of quantum transport in chaotic cavities
The problem of quantum transport in chaotic cavities with broken
time-reversal symmetry is shown to be completely integrable in the universal
limit. This observation is utilised to determine the cumulants and the
distribution function of conductance for a cavity with ideal leads supporting
an arbitrary number of propagating modes. Expressed in terms of solutions
to the fifth Painlev\'e transcendent and/or the Toda lattice equation, the
conductance distribution is further analysed in the large- limit that
reveals long exponential tails in the otherwise Gaussian curve.Comment: 4 pages; final version to appear in Physical Review Letter
The 1/3-shot noise suppression in diffusive nanowires
We report low-temperature shot noise measurements of short diffusive Au wires
attached to electron reservoirs of varying sizes. The measured noise
suppression factor compared to the classical noise value
strongly depends on the electric heat conductance of the reservoirs. For small
reservoirs injection of hot electrons increases the measured noise and hence
the suppression factor. The universal 1/3-suppression factor can only
asymptotically be reached for macroscopically large and thick electron
reservoirs. A heating model based on the Wiedemann-Franz law is used to explain
this effect.Comment: 10 figure
Shot noise in ferromagnet--normal metal systems
A semiclassical theory of the low frequency shot noise in ferromagnet -
normal metal systems is formulated. Non-collinear magnetization directions of
the ferromagnetic leads, arbitrary junctions and the elastic and inelastic
scattering regimes are considered. The shot noise is governed by a set of
mesoscopic parameters that are expressed in terms of the microscopic details of
the junctions in the circuit. Explicit results in the case of ballistic,
tunnel, and diffusive junctions are evaluated. The shot noise, the current and
the Fano factor are calculated for a double barrier ferromagnet - normal metal
- ferromagnet system. It is demonstrated that the shot noise can have a
non-monotonic behavior as a function of the relative angle between the
magnetizations of the ferromagnetic reservoirs.Comment: 17 pages, 7 figure
Shot Noise by Quantum Scattering in Chaotic Cavities
We have experimentally studied shot noise of chaotic cavities defined by two
quantum point contacts in series. The cavity noise is determined as 1/4*2e|I|
in agreement with theory and can be well distinguished from other contributions
to noise generated at the contacts. Subsequently, we have found that cavity
noise decreases if one of the contacts is further opened and reaches nearly
zero for a highly asymmetric cavity.Comment: 4 pages, 4 figures, REVTe
Systematic approach to statistics of conductance and shot-noise in chaotic cavities
Applying random matrix theory to quantum transport in chaotic cavities, we
develop a novel approach to computation of the moments of the conductance and
shot-noise (including their joint moments) of arbitrary order and at any number
of open channels. The method is based on the Selberg integral theory combined
with the theory of symmetric functions and is applicable equally well for
systems with and without time-reversal symmetry. We also compute higher-order
cumulants and perform their detailed analysis. In particular, we establish an
explicit form of the leading asymptotic of the cumulants in the limit of the
large channel numbers. We derive further a general Pfaffian representation for
the corresponding distribution functions. The Edgeworth expansion based on the
first four cumulants is found to reproduce fairly accurately the distribution
functions in the bulk even for a small number of channels. As the latter
increases, the distributions become Gaussian-like in the bulk but are always
characterized by a power-law dependence near their edges of support. Such
asymptotics are determined exactly up to linear order in distances from the
edges, including the corresponding constants.Comment: 14 pages, 4 figures, 3 table
Can filesharers be triggered by economic incentives? Results of an experiment
Illegal filesharing on the internet leads to considerable financial losses for artists and copyright owners as well as producers and sellers of music. Thus far, measures to contain this phenomenon have been rather restrictive. However, there are still a considerable number of illegal systems, and users are able to decide quite freely between legal and illegal downloads because the latter are still difficult to sanction. Recent economic approaches account for the improved bargaining position of users. They are based on the idea of revenue-splitting between professional sellers and peers. In order to test such an innovative business model, the study reported in this article carried out an experiment with 100 undergraduate students, forming five small peer-to-peer networks.The networks were confronted with different economic conditions.The results indicate that even experienced filesharers hold favourable attitudes towards revenue-splitting.They seem to be willing to adjust their behaviour to different economic conditions
The effect of cigarette smoke exposure on the development of inflammation in lungs, gut and joints of TNFÎARE mice
The inflammatory cytokine TNF-alpha is a central mediator in many immune-mediated diseases, such as Crohn's disease (CD), spondyloarthritis (SpA) and chronic obstructive pulmonary disease (COPD). Epidemiologic studies have shown that cigarette smoking (CS) is a prominent common risk factor in these TNF-dependent diseases. We exposed TNF Delta ARE mice; in which a systemic TNF-alpha overexpression leads to the development of inflammation; to 2 or 4 weeks of air or CS. We investigated the effect of deregulated TNF expression on CS-induced pulmonary inflammation and the effect of CS exposure on the initiation and progression of gut and joint inflammation. Upon 2 weeks of CS exposure, inflammation in lungs of TNF Delta ARE mice was significantly aggravated. However, upon 4 weeks of CS-exposure, this aggravation was no longer observed. TNF Delta ARE mice have no increases in CD4+ and CD8+ T cells and a diminished neutrophil response in the lungs after 4 weeks of CS exposure. In the gut and joints of TNF Delta ARE mice, 2 or 4 weeks of CS exposure did not modulate the development of inflammation. In conclusion, CS exposure does not modulate gut and joint inflammation in TNF Delta ARE mice. The lung responses towards CS in TNF Delta ARE mice however depend on the duration of CS exposure
Multi-objective calibration of RothC using measured carbon stocks and auxiliary data of a long-term experiment in Switzerland
Interactions between model parameters and low spatiotemporal resolution of available data mean that conventional soil organic carbon (SOC) models are often affected by equifinality, with consequent uncertainty in SOC forecasts. Estimation of belowground C inputs is another major source of uncertainty in SOC modelling. Models are usually calibrated on SOC stocks and fluxes from longâterm experiments (LTEs), whereas other point data are not used for constraining the model parameters. We used data from an agricultural longâterm (> 65 years) fertilization experiment to test a multiâobjective parameter estimation approach on the RothC model, combining SOC data from different fertilization treatments with microbial biomass, basal respiration and Zimmermannâs fractions data. We also compared two methods to estimate the belowground C inputs: a conventional scaling of belowground biomass from crop harvest yield and an alternative approach based on constant belowground C for cereals measured experimentally in the field. The resulting posterior parameter distributions still suffered from some equifinality; the most stable C pool kinetic constants and composition of exogenous organic matter were the most sensitive parameters. The use of fixed belowground C inputs for cereals improved the model performance, reducing the importance of treatmentâspecific parameters and processes. The introduction of microbial biomass and basal respiration data was effective for increasing determination of the calibration, but also suggested a change in the model structure: the microbial biomass pool, which is proportional to the C inputs in the traditional models, could be represented by different microbial physiology functions
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