7,165 research outputs found
Electron-phonon coupling in metallic carbon nanotubes: Dispersionless electron propagation despite dissipation
A recent study [Rosati, Dolcini, and Rossi, Appl. Phys. Lett. 106, 243101
(2015)] has predicted that, while in semiconducting single-walled carbon
nanotubes (SWNTs) an electronic wave packet experiences the typical spatial
diffusion of conventional materials, in metallic SWNTs its shape remains
essentially unaltered up to micron distances at room temperature, even in the
presence of the electron-phonon coupling. Here, by utilizing a Lindblad-based
density-matrix approach enabling us to account for both dissipation and
decoherence effects, we test such prediction by analyzing various aspects that
were so far unexplored. In particular, accounting for initial nonequilibrium
excitations, characterized by an excess energy , and including both intra-
and interband phonon scattering, we show that for realistically high values of
the electronic diffusion is extremely small and nearly independent of its
energetic distribution, in spite of a significant energy-dissipation and
decoherence dynamics. Furthermore, we demonstrate that the effect is robust
with respect to the variation of the chemical potential. Our results thus
suggest that metallic SWNTs are a promising platform to realise quantum
channels for the non-dispersive transmission of electronic wave packets.Comment: 14 pages, 7 figure
Quintessential Enhancement of Dark Matter Abundance
The presence of a dynamical scalar field in the early universe could significantly affect the `freeze-out' time of particle species. In particular, it was recently shown that an enhancement of the relic abundance of neutralinos can be produced in this way. We examine under which conditions this primordial scalar field could be identified with the Quintessence scalar and find, through concrete examples, that modifications to the standard paradigm are necessary. We discuss two possible variations: the presence of more scalars and the switching on of an interaction
Renormalization Group Approach to Spin Glass Systems
A renormalization group transformation suitable for spin glass models and,
more generally, for disordered models, is presented. The procedure is
non-standard in both the nature of the additional interactions and the coarse
graining transformation, that is performed on the overlap probability measure
(which is clearly non-Gibbsian). Universality classes are thus naturally
defined on a large set of models, going from and Gaussian spin glasses
to Ising and fully frustrated models, and others.Comment: 12 pages, 4 figure
Weak proton capture on 3He
The astrophysical S-factor for the proton weak capture on 3He is calculated
with correlated-hyperspherical-harmonics bound and continuum wave functions
corresponding to realistic Hamiltonians consisting of the Argonne v14 or
Argonne v18 two-nucleon and Urbana-VIII or Urbana-IX three-nucleon
interactions. The nuclear weak charge and current operators have vector and
axial-vector components, that include one- and many-body terms. All possible
multipole transitions connecting any of the p 3He S- and P-wave channels to the
4He bound state are considered. The S-factor at a p 3He center-of-mass energy
of 10 keV, close to the Gamow-peak energy, is predicted to be 10.1 10^{-20} keV
b with the AV18/UIX Hamiltonian, a factor of about 4.5 larger than the value
adopted in the standard solar model. The P-wave transitions are found to be
important, contributing about 40 % of the calculated S-factor. The energy
dependence is rather weak: the AV18/UIX zero-energy S-factor is 9.64 10^{-20}
keV b, only 5 % smaller than the 10 keV result quoted above. The model
dependence is also found to be weak: the zero-energy S-factor is calculated to
be 10.2 10^{-20} keV b with the older AV14/UVIII model, only 6 % larger than
the AV18/UIX result. Our best estimate for the S-factor at 10 keV is therefore
(10.1 \pm 0.6) 10^{-20} keV b, when the theoretical uncertainty due to the
model dependence is included. This value for the calculated S-factor is not as
large as determined in fits to the Super-Kamiokande data in which the hep flux
normalization is free. However, the precise calculation of the S-factor and the
consequent absolute prediction for the hep neutrino flux will allow much
greater discrimination among proposed solar neutrino oscillation solutions.Comment: 54 pages RevTex file, 6 PostScript figures, submitted to Phys. Rev.
SUSY QCD and Quintessence
Recent data point in the direction of a cosmological constant dominated universe. We investigate the role of supersymmetric QCD with N_f 1, the multiscalar dynamics is fully taken into account, showing that a certain degree of flavor symmetry in the initial conditions is necessary in order to attain the required late-time ``tracking'' attractor behavior. A possible solution to the problem of long-range interactions of gravitational strength is proposed. Finally we show how, as a consequence of the interaction with the Standard Model fields, the early cosmological evolution of the scalar fields may be dramatically altered, and the approach to the tracking behavior may become much more efficient
Theoretical Estimation of CO2 Compression and Transport Costs for an Hypothetical Carbon and Capture & Storage Requalification of the Saline Joniche Power Plant Project
SEI S.p.a. presented a project to build a 1320 MW coal-fired power plant in Saline Joniche, on the Southern tip of Calabria Region, Italy, in 2008. A gross early evaluation about the possibility to add CCS (CO2 Capture & Storage) was performed too. The project generated widespread opposition among environmental associations, citizens and local institutions in that period, against the coal use to produce energy, as a consequence of its GHG clima-alterating impact. Moreover the CCS (also named Carbon Capture & Storage or more recently CCUS: Carbon Capture-Usage-Storage) technology was at that time still an unknown and “mysterious” solution for the GHG avoiding to the atmosphere.  The present study concerns the sizing of the compression and transportation system of the CCS section, included in the project presented at the time by SEI Spa; the sizing of the compression station and the pipeline connecting the plant to the possible Fosca01 offshore injection site previously studied as a possible storage solution, as part of a coarse screening of CO2 storage sites in the Calabria Region. This study takes into account the costs of construction, operation and maintenance (O&M) of both the compression plant and the sound pipeline, considering the gross static storage capacity of the Fosca01 reservoir as a whole as previously evaluated
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