2,698 research outputs found
Narrow-escape times for diffusion in microdomains with a particle-surface affinity: Mean-field results
We analyze the mean time t_{app} that a randomly moving particle spends in a
bounded domain (sphere) before it escapes through a small window in the
domain's boundary. A particle is assumed to diffuse freely in the bulk until it
approaches the surface of the domain where it becomes weakly adsorbed, and then
wanders diffusively along the boundary for a random time until it desorbs back
to the bulk, and etc. Using a mean-field approximation, we define t_{app}
analytically as a function of the bulk and surface diffusion coefficients, the
mean time it spends in the bulk between two consecutive arrivals to the surface
and the mean time it wanders on the surface within a single round of the
surface diffusion.Comment: 8 pages, 1 figure, submitted to JC
Compost and digestate: sustainability, benefits, impacts for the environment and for plant production
This proceedings volume contains the papers presented at the CODIS 2008 congress held on 27 - 29 February 2008 in Solothurn (Switzerland).The composting and digestion of biogenic waste materials and the subsequent application of compost and digestate to soil contributes to nutrient recycling and renewable energy production. Moreover, compost and digestate can improve soil fertility and suppress plant diseases. On the other hand, compost and digestate may also contain a variety of pollutants hazardous to soil, such as heavy metals and organic contaminants.Compost and digestate have been thoroughly investigated in the framework of two associated projects entitled Organic Pollutants in Compost and Digestate in Switzerland and Effects of Composts and Digestate on the Environment, Soil Fertility and Plant Health. These projects yielded new insights into the properties of compost and digestate, mainly with regard to biological parameters and the occurrence of both classic and emerging organic pollutants.The CODIS 2008 congress was the final event of these two projects
Quantum Hall fractions for spinless Bosons
We study the Quantum Hall phases that appear in the fast rotation limit for
Bose-Einstein condensates of spinless bosonic atoms. We use exact
diagonalization in a spherical geometry to obtain low-lying states of a small
number of bosons as a function of the angular momentum. This allows to
understand or guess the physics at a given filling fraction nu, ratio of the
number of bosons to the number of vortices. This is also the filling factor of
the lowest Landau level. In addition to the well-known Bose Laughlin state at
nu =1/2 we give evidence for the Jain principal sequence of incompressible
states at nu =p/(p+- 1) for a few values of p. There is a collective mode in
these states whose phenomenology is in agreement with standard arguments coming
e.g. from the composite fermion picture. At filling factor one, the potential
Fermi sea of composite fermions is replaced by a paired state, the Moore-Read
state. This is most clearly seen from the half-flux nature of elementary
excitations. We find that the hierarchy picture does not extend up to the point
of transition towards a vortex lattice. While we cannot conclude, we
investigate the clustered Read-Rezayi states and show evidence for
incompressible states at the expected ratio of flux vs number of Bose
particles.Comment: RevTeX 4, 11 pages, 13 figure
Gesunder Boden - gesunde Pflanzen
Obwohl viele ältere Biobetriebe kleinere Nährstoffgehalte im Boden aufwiesen, waren diese noch nicht ertragsbegrenzend. Die abnehmenden Nährstoffgehalte im Boden und den Pflanzen zeigen, dass regelmässige Bodenanalysen auf dem Biobetrieb nötig sind. Die Suppressivität der Böden hing nicht direkt von den Biojahren ab. Durch die Gestaltung der Fruchtfolge und den Hofdüngereinsatz lässt sie sich aber steigern. Der Zusammenhang zwischen Bewirtschaftung Bodeneigenschaften und der Suppressivität muss genauer untersucht werden
Potential of different composts to improve soil fertility
Composts can influence soil fertility and plant health. These influences can be positive or negative, depending of the quality of the composts. Some practitioners already make use of the positive effects on plant health. For example, they use composts to protect their plants against soil borne diseases in substrate, or to detoxify and reactivate soil after steaming. In order to estimate the potential of Swiss composts to influence
soil fertility and plant health positively, we analyzed one hundred composts representative of the different composting systems and qualities available on the market.
The organic substance and the nutrient content of the composts varied greatly between the composts; the materials of origin were the major factor influencing these values. The respiration rate and enzyme activities also varied greatly, particularly in the youngest composts. These differences become smaller when the composts become more mature. Maturity, the degradation stage of the organic matter, depended not only on the age of the compost, but also on the management of the process. The N-mineralization potential from compost added to soil showed that a high proportion of young composts immobilized the nitrogen in the soil. This problem was hardly correlated with the materials of origin, but with the management of the first stage of the composting
process. Especially composts which had become too dry in this period lost their ammonia-nitrogen, and hence immobilized nitrogen in the soil. Also composts with a low NO3/NH4 ratio, as a rough indicator for an immature compost, immobilized nitrogen in the soil. By contrast, the phytotoxicity of the composts varied very much also in matured composts, showing that the storage of the compost plays a decisive role. While the
majority of compost protected cucumber plants against Pythium ultimum, only a few composts suppressed Rhizoctonia solani in basil. With respect to disease suppression, the management of the maturation process seems to play a major role.
In conclusion, big differences in compost quality and of their impact on soil fertility and on plant health were observed. The management of the composting process seems to influence the quality of the composts to a higher extent than the materials of origin or the composting system. More attention should be paid to biological quality of composts, in order to produce composts with more beneficial effects on crops
Frequency comparisons and absolute frequency measurements of 171Yb+ single-ion optical frequency standards
We describe experiments with an optical frequency standard based on a laser
cooled Yb ion confined in a radiofrequency Paul trap. The
electric-quadrupole transition from the ground state to the
state at the wavelength of 436 nm is used as the reference
transition. In order to compare two Yb standards, separate
frequency servo systems are employed to stabilize two probe laser frequencies
to the reference transition line centers of two independently stored ions. The
experimental results indicate a relative instability (Allan standard deviation)
of the optical frequency difference between the two systems of only, so that shifts in the sub-hertz range can be
resolved. Shifts of several hertz are observed if a stationary electric field
gradient is superimposed on the radiofrequency trap field. The absolute optical
transition frequency of Yb at 688 THz was measured with a cesium atomic
clock at two times separated by 2.8 years. A temporal variation of this
frequency can be excluded within a relative uncertainty of yr. Combined with recently published values for the constancy
of other transition frequencies this measurement provides a limit on the
present variability of the fine structure constant at the level of
yr.Comment: 12 pages, 5 figures, Proceedings of MPLP'04, Novosibirsk, August
22.-27., 200
Impact of soil management practices on soil fertility and disease suppressiveness
Soil management practices are targeted to provide adequate crop nutrition and to ensure durable soil fertility and to avoid negative environmental impacts. Soil management also aims to reduce pest and disease pressure on crops. Organic farming is believed to increase soil suppressiveness towards soil-borne diseases as well aerial diseases. In this paper we will discuss the potential of soil manage-ment as a tool to improve disease suppressiveness in practice
Vibrational Tamm states at the edges of graphene nanoribbons
We study vibrational states localized at the edges of graphene nanoribbons.
Such surface oscillations can be considered as a phonon analog of Tamm states
well known in the electronic theory. We consider both armchair and zigzag
graphene stripes and demonstrate that surface modes correspond to phonons
localized at the edges of the graphene nanoribbon, and they can be classified
as in-plane and out-of-plane modes. In addition, in armchair nanoribbons
anharmonic edge modes can experience longitudinal localization in the form of
self-localized nonlinear modes, or surface breather solitons.Comment: 10 pages, 10 figure
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