6,725 research outputs found
Evidence of 1D behaviour of He confined within carbon-nanotube bundles
We present the first low-temperature thermodynamic investigation of the
controlled physisorption of He gas in carbon single-wall nanotube (SWNT)
samples. The vibrational specific heat measured between 100 mK and 6 K
demonstrates an extreme sensitivity to outgassing conditions. For bundles with
a few number of NTs the extra contribution to the specific heat, C,
originating from adsorbed He at very low density displays 1D behavior,
typical for He atoms localized within linear channels as grooves and
interstitials, for the first time evidenced. For larger bundles, C
recovers the 2D behaviour akin to the case of He films on planar
substrates (grafoil).Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let
Non-Collinear Ferromagnetic Luttinger Liquids
The presence of electron-electron interactions in one dimension profoundly
changes the properties of a system. The separation of charge and spin degrees
of freedom is just one example. We consider what happens when a system
consisting of a ferromagnetic region of non-collinearity, i.e. a domain wall,
is coupled to interacting electrons in one-dimension (more specifically a
Luttinger liquid). The ferromagnetism breaks spin charge separation and the
presence of the domain wall introduces a spin dependent scatterer into the
problem. The absence of spin charge separation and the effects of the electron
correlations results in very different behaviour for the excitations in the
system and for spin-transfer-torque effects in this model.Comment: 6 pages, submitted to Journal of Physics: Conference Series for JEMS
201
Nonequilibrium fluctuation-dissipation relations for one- and two-particle correlation functions in steady-state quantum transport
We study the non-equilibrium (NE) fluctuation-dissipation (FD) relations in
the context of quantum thermoelectric transport through a two-terminal
nanodevice in the steady-state. The FD relations for the one- and two-particle
correlation functions are derived for a model of the central region consisting
of a single electron level. Explicit expressions for the FD relations of the
Green's functions (one-particle correlations) are provided. The FD relations
for the current-current and charge-charge (two-particle) correlations are
calculated numerically. We use self-consistent NE Green's functions
calculations to treat the system in the absence and in the presence of
interaction (electron-phonon) in the central region. We show that, for this
model, there is no single universal FD theorem for the NE steady state. There
are different FD relations for each different class of problems. We find that
the FD relations for the one-particle correlation function are strongly
dependent on both the NE conditions and the interactions, while the FD
relations of the current-current correlation function are much less dependent
on the interaction. The latter property suggests interesting applications for
single-molecule and other nanoscale transport experiments.Comment: This revised version is now accepted for publication in the Journal
of Chemical Physics (March 2014). arXiv admin note: text overlap with
arXiv:1305.507
Adsorption and Specific-Heat Studies of Monolayer and Submonolayer Films of He3 and He4
A study has been made of the adsorption of He3 and He4 at 4°K on a substrate consisting of a monolayer of argon adsorbed on a sintered copper sponge. The isotherms display distinct steps indicating the completion of first and second adsorbed layers. Comparisons among the adsorption isotherms of helium and of Ar and N2 at 77.4°K yield a self-consistent set of molecular areas. Measurements have been made of the specific heat of five submonolayer coverages of He3 and He4 on Ar-plated Cu sponge. The heat capacities of nearly complete monolayers vary as T2 from 0.3 to 4°K, yielding two-dimensional Debye temperatures Theta (He4)=28±1°K, and Theta (He3)=31±1°K. At lower coverages the molar heat capacities increase and develop contributions linear in T below 1°K. At an intermediate coverage, the heat capacity of He4 exhibits a broad and pronounced maximum near 3°K. Possible mechanisms for the linear terms and the maximum are discussed briefly. Evidence for considerable mobility of He atoms along the surface is adduced from the temperature and coverage dependence of the heat capacity. The T2 behavior for the complete monolayers yields an upper limit of ~10^-11 sec for the lifetime of a He atom in any individual adsorption site, consistent with a theoretical estimate
Generalized information entropies depending only on the probability distribution
Systems with a long-term stationary state that possess as a spatio-temporally
fluctuation quantity can be described by a superposition of several
statistics, a "super statistics". We consider first, the Gamma, log-normal and
-distributions of . It is assumed that they depend only on , the
probability associated with the microscopic configuration of the system. For
each of the three distributions we calculate the Boltzmann factors and
show that they coincide for small variance of the fluctuations. For the Gamma
distribution it is possible to calculate the entropy in a closed form,
depending on , and to obtain then an equation relating with . We also propose, as other examples, new entropies close related with the
Kaniadakis and two possible Sharma-Mittal entropies. The entropies presented in
this work do not depend on a constant parameter but on . For the
-Gamma distribution and its corresponding Boltzmann factor
and the associated entropy, we show the validity of the saddle-point
approximation. We also briefly discuss the generalization of one of the four
Khinchin axioms to get this proposed entropy.Comment: 13 pages, 3 figure
Does Luttinger liquid behaviour survive in an atomic wire on a surface?
We form a highly simplified model of an atomic wire on a surface by the
coupling of two one-dimensional chains, one with electron-electron interactions
to represent the wire and and one with no electron-electron interactions to
represent the surface. We use exact diagonalization techniques to calculate the
eigenstates and response functions of our model, in order to determine both the
nature of the coupling and to what extent the coupling affects the Luttinger
liquid properties we would expect in a purely one-dimensional system. We find
that while there are indeed Luttinger liquid indicators present, some residual
Fermi liquid characteristics remain.Comment: 14 pages, 7 figures. Submitted to J Phys
Land cover classification using multi-temporal MERIS vegetation indices
The spectral, spatial, and temporal resolutions of Envisat's Medium Resolution Imaging Spectrometer (MERIS) data are attractive for regional- to global-scale land cover mapping. Moreover, two novel and operational vegetation indices derived from MERIS data have considerable potential as discriminating variables in land cover classification. Here, the potential of these two vegetation indices (the MERIS global vegetation index (MGVI), MERIS terrestrial chlorophyll index (MTCI)) was evaluated for mapping eleven broad land cover classes in Wisconsin. Data acquired in the high and low chlorophyll seasons were used to increase inter-class separability. The two vegetation indices provided a higher degree of inter-class separability than data acquired in many of the individual MERIS spectral wavebands. The most accurate landcover map (73.2%) was derived from a classification of vegetation index-derived data with a support vector machine (SVM), and was more accurate than the corresponding map derived from a classification using the data acquired in the original spectral wavebands
Universal low-energy properties of three two-dimensional particles
Universal low-energy properties are studied for three identical bosons
confined in two dimensions. The short-range pair-wise interaction in the
low-energy limit is described by means of the boundary condition model. The
wave function is expanded in a set of eigenfunctions on the hypersphere and the
system of hyper-radial equations is used to obtain analytical and numerical
results. Within the framework of this method, exact analytical expressions are
derived for the eigenpotentials and the coupling terms of hyper-radial
equations. The derivation of the coupling terms is generally applicable to a
variety of three-body problems provided the interaction is described by the
boundary condition model. The asymptotic form of the total wave function at a
small and a large hyper-radius is studied and the universal logarithmic
dependence in the vicinity of the triple-collision point is
derived. Precise three-body binding energies and the scattering length
are calculated.Comment: 30 pages with 13 figure
Classical rotational inertia of solid helium 4
The observation of reduced rotational inertia in a cell containing solid
helium 4 has been interpreted as evidence for superfluidity of the solid. An
alternative explanation is slippage of the solid at the container wall due to
grain boundary premelting between the solid and dense adsorbed layers at the
container wall. We calculate the range of film thickness and the viscous drag,
and find that the slippage can account for the observations.Comment: 4 pages, 1 figur
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