423 research outputs found
Generation of localized magnetic moments in the charge-density-wave state
We propose a mechanism explaining the generation of localized magnetic
moments in charge-density-wave compounds. Our model Hamiltonian describes an
Anderson impurity placed in a host material exhibiting the charge-density wave.
There is a region of the model's parameter space, where even weak Coulomb
repulsion on the impurity site is able to localize the magnetic moment on the
impurity. The phase diagram of a single impurity at T=0 is mapped. To establish
the connection with experiment thermodynamic properties of a random impurity
ensemble is studied. Magnetic susceptibility of the ensemble diverges at low
temperature; heat capacity as a function of the magnetic field demonstrates
pronounced low field peak. Both features are consistent with experiments on
orthorhombic TaS3 and blue bronze.Comment: 8 pages, 7 figure
Influence of the particle shape on the equilibrium morphologies of supracolloidal magnetic filaments
We investigate the equilibrium morphologies of linear and ring-shaped
magnetic filaments made from crosslinked ferromagnetic spherical or ellipsoidal
colloidal particles. Using Langevin dynamics simulations, we calculate the
radius of gyration and total magnetic moment of a single filament at zero field
and different temperatures, analyzing the influence of the particles shape, the
strength of their magnetic moment and the filament length. Our results show
that, among such parameters, the shape of the particles has the strongest
qualitative impact on the equilibrium behavior of the filaments
Electronic properties of the armchair graphene nanoribbon
We investigate the electronic band structure of an undoped graphene armchair
nanoribbon. We demonstrate that such nanoribbon always has a gap in its
electronic spectrum. Indeed, even in the situations where simple
single-electron calculations predict a metallic dispersion, the system is
unstable with respect to the deformation of the carbon-carbon bonds dangling at
the edges of the armchair nanoribbon. The edge bonds' deformation couples
electron and hole states with equal momentum. This coupling opens a gap at the
Fermi level. In a realistic sample, however, it is unlikely that this
instability could be observed in its pure form. Namely, since chemical
properties of the dangling carbon atoms are different from chemical properties
of the atoms inside the sample (for example, the atoms at the edge have only
two neighbours, besides additional non-carbon atoms might be attached to
passivate unpaired covalent carbon bonds), it is very probable that the bonds
at the edge are deformed due to chemical interactions. This chemically-induced
modification of the nanoribbon's edges can be viewed as an effective field
biasing our predicted instability in a particular direction. Yet by disordering
this field (e.g., through random substitution of the radicals attached to the
edges) we may tune the system back to the critical regime and vary the
electronic properties of the system. For example, we show that electrical
transport through a nanoribbon is strongly affected by such disorder.Comment: 12 pages, 4 figur
Aggregated estimation of the basic parameters of biological production and the carbon budget of Russian terrestrial ecosytems: 2. Net primary production
The estimated net primary production (NPP) of Russian terrestrial ecosystems (annual average over the period from 1988 to 1992) is 9544 Tg of dry matter, or 4353 Tg of carbon. Of the total amount, forests account for approximately 39.2% (here and below, comparisons are made with respect to carbon content); natural grasslands and brushwoods, for 27.6%; farmlands (arable land and cultivated pastures), for 22.0%; and wetlands, for 11.2%. The average NPP density on lands covered with vegetation (1629.8 million hectares in Russia) is 267 g C/m2per year. The highest value (498 g C/m2per year) is characteristic of arable lands. Other land-use/land-cover (LULC) classes have the following NPP densities (in areas covered with vegetation): grasslands and brushwoods, 278 g C/m2; forests, 224 g C/m2; and wetlands, 219 g C/m2per year. In general, Russian terrestrial ecosystems accumulate 59.7% of the total NPP in the aboveground phytomass (47.8% in green parts and 11.9% in wood) and 40.3% in the underground phytomass. The latter parameter differs significantly in different LULC classes and bioclimatic zones. According to calculations, the uncertainty in estimating the total NPP is 11% (a priori confidential probability 0.9)
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