2,044 research outputs found
Omreglering sÄ att (nÀstan) alla blir vinnare
I denna artikel diskuterar vi nÄgra av de konflikter som rÄder kring vattenkraften. En omreglering sÄdan att i princip alla vinner presenteras. Förslaget tillÀmpas pÄ Ljusnan dÀr tvÄ dammar vid utloppet föreslÄs bli utrivna och kraftverksÀgaren kompenseras med en utbyggnad 15 mil uppströms. Lax och andra arter kan dÄ vandra 15 mil uppströms för lek. Vidare förbÀttras rekreationsmöjligheterna för de kringboende
Cabrera-Mott kinetics of oxidation of metal nanowires
The Cabrera-Mott model, implying that oxidation of a metal is limited by the field-facilitated activated jumps of metal ions at the metal-oxide interface, was originally proposed to interpret growth of thin oxide films on planar metal surfaces. Recently, the model was used to describe oxidation of spherical nanoparticles with small radius of curvature. Here, we analyze oxidation of nanowires. The increase of the oxide thickness with increasing time for a nanowire is shown to be slower than that for a nanoparticle with the same radius, but faster than in the case of a planar surface
Towards a working density-functional theory for polymers: First-principles determination of the polyethylene crystal structure
Equilibrium polyethylene crystal structure, cohesive energy, and elastic
constants are calculated by density-functional theory applied with a recently
proposed density functional (vdW-DF) for general geometries [Phys. Rev. Lett.
92, 246401 (2004)] and with a pseudopotential-planewave scheme. The vdW-DF with
its account for the long-ranged van der Waals interactions gives not only a
stabilized crystal structure but also values of the calculated lattice
parameters and elastic constants in quite good agreement with experimental
data, giving promise for successful application to a wider range of polymers.Comment: 4 pages, 3 figure
Influence of van der Waals forces on the adsorption structure of benzene on silicon studied using density functional theory
Two different adsorption configurations of benzene on the Si(001)-(2 x 1) surface, the tight-bridge and butterfly structures, were studied using density functional theory. Several exchange and correlation functionals were used, including the recently developed van der Waals density functional (vdW-DF), which accounts for the effect of van der Waals forces. In contrast to the Perdew-Burke-Ernzerhof (PBE), revPBE, and other generalized-gradient approximation functionals, the vdW-DF finds that, for most coverages, the adsorption energy of the butterfly structure is greater than that of the tight-bridge structure
Superembeddings, Non-Linear Supersymmetry and 5-branes
We examine general properties of superembeddings, i.e., embeddings of
supermanifolds into supermanifolds. The connection between an embedding
procedure and the method of non-linearly realised supersymmetry is clarified,
and we demonstrate how the latter arises as a special case of the former. As an
illustration, the super-5-brane in 7 dimensions, containing a self-dual 3-form
world-volume field strength, is formulated in both languages, and provides an
example of a model where the embedding condition does not suffice to put the
theory on-shell.Comment: plain tex, 28 p
Visualisation of ectomycorrhizal rhizomorph structure using laser scanning confocal microscopy
A method for the observation of the three-dimensional structure of intact ectomycorrhizal rhizomorphs is described. The method is based on a combination of clearing the material with KOH followed by staining with congo red and subsequent imaging under a laser scanning confocal microscope (LSCM). The images obtained are of a much higher three-dimensional resolution than those obtained previously by use of conventional light microscopical techniques. The structure of highly differentiated and undifferentiated rhizomorphs is described. Applications of the method are briefly discussed
Comparison of near-interface traps in AlO/4H-SiC and AlO/SiO/4H-SiC structures
Aluminum oxide (Al2O3) has been grown by atomic layer deposition on n-type
4H-SiC with and without a thin silicon dioxide (SiO2) intermediate layer. By
means of Capacitance Voltage and Thermal Dielectric Relaxation Current
measurements, the interface properties have been investigated. Whereas for the
samples with an interfacial SiO2 layer the highest near-interface trap density
is found at 0.3 eV below the conduction band edge, Ec, the samples with only
the Al2O3 dielectric exhibit a nearly trap free region close to Ec. For the
Al2O3/SiC interface, the highest trap density appears between 0.4 to 0.6 eV
below Ec. The results indicate the possibility for SiC-based MOSFETs with Al2O3
as the gate dielectric layer in future high performance devices.Comment: 3 figures. Applied Physics Letters, accepted for publicatio
Nonlinear propagation of light in Dirac matter
The nonlinear interaction between intense laser light and a quantum plasma is
modeled by a collective Dirac equation coupled with the Maxwell equations. The
model is used to study the nonlinear propagation of relativistically intense
laser light in a quantum plasma including the electron spin-1/2 effect. The
relativistic effects due to the high-intensity laser light lead, in general, to
a downshift of the laser frequency, similar to a classical plasma where the
relativistic mass increase leads to self-induced transparency of laser light
and other associated effects. The electron spin-1/2 effects lead to a frequency
up- or downshift of the electromagnetic (EM) wave, depending on the spin state
of the plasma and the polarization of the EM wave. For laboratory solid density
plasmas, the spin-1/2 effects on the propagation of light are small, but they
may be significant in super-dense plasma in the core of white dwarf stars. We
also discuss extensions of the model to include kinetic effects of a
distribution of the electrons on the nonlinear propagation of EM waves in a
quantum plasma.Comment: 9 pages, 2 figure
Size-Dependent Kinetics of Hydriding and Dehydriding of Pd Nanoparticles
Using a new indirect nanoplasmonic sensing method with subsecond resolution, we have studied hydriding and dehydriding kinetics of Pd nanoparticles in the size range 1.8-5.4 nm. Strong particle-size effects are observed. The scaling of the hydriding and dehydriding time scales satisfies power and power-exponential laws. The former (with an exponent of 2.9) is in perfect agreement with Monte Carlo simulations of diffusion-controlled hydriding kinetics. The latter is explained by the effect of surface tension on hydrogen desorption from the surface layer. The approach is generalizable to other reactant-nanoparticle systems
Numerical simulations of the Fourier transformed Vlasov-Maxwell system in higher dimensions --- Theory and applications
We present a review of recent developments of simulations of the
Vlasov-Maxwell system of equations using a Fourier transform method in velocity
space. In this method, the distribution functions for electrons and ions are
Fourier transformed in velocity space, and the resulting set of equations are
solved numerically. In the original Vlasov equation, phase mixing may lead to
an oscillatory behavior and sharp gradients of the distribution function in
velocity space, which is problematic in simulations where it can lead to
unphysical electric fields and instabilities and to the recurrence effect where
parts of the initial condition recur in the simulation. The particle
distribution function is in general smoother in the Fourier transformed
velocity space, which is desirable for the numerical approximations. By
designing outflow boundary conditions in the Fourier transformed velocity
space, the highest oscillating terms are allowed to propagate out through the
boundary and are removed from the calculations, thereby strongly reducing the
numerical recurrence effect. The outflow boundary conditions in higher
dimensions including electromagnetic effects are discussed. The Fourier
transform method is also suitable to solve the Fourier transformed Wigner
equation, which is the quantum mechanical analogue of the Vlasov equation for
classical particles.Comment: 41 pages, 19 figures. To be published in Transport Theory and
Statistical Physics. Proceedings of the VLASOVIA 2009 Workshop, CIRM, Luminy,
Marseilles, France, 31 August - 4 September 200
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