3,381 research outputs found
Dynamical Mean-Field Study of the Ferromagnetic Transition Temperature of a Two-Band Model for Colossal Magnetoresistance Materials
The ferromagnetic (FM) transition temperature (Tc) of a two-band
Double-Exchange (DE) model for colossal magnetoresistance (CMR) materials is
studied using dynamical mean-field theory (DMFT), in wide ranges of coupling
constants, hopping parameters, and carrier densities. The results are shown to
be in excellent agreement with Monte Carlo simulations. When the bands overlap,
the value of Tc is found to be much larger than in the one-band case, for all
values of the chemical potential within the energy overlap interval. A nonzero
interband hopping produces an additional substantial increase of Tc, showing
the importance of these nondiagonal terms, and the concomitant use of multiband
models, to boost up the critical temperatures in DE-based theories.Comment: 4 pages, 4 eps figure
Generalized quantum measurements and local realism
The structure of a local hidden variable model for experiments involving
sequences of measurements rigorously is analyzed. Constraints imposed by local
realism on the conditional probabilities of the outcomes of such measurement
schemes are explicitly derived. The violation of local realism in the case of
``hidden nonlocality'' is illustrated by an operational example.Comment: Revtex, 12 pages; Some modifications of introduction has been made; a
note stating that part of results had been obtained earlier by other authors,
has been added; one postscript figure available at request from
[email protected]
A platform for crowdsourcing corpora for argumentative
One problem that Argument Mining (AM) is facing is the difficultyof obtaining suitable annotated corpora. We propose a web-basedplatform, BookSafari, that allows crowdsourcing of annotated cor-pora forrelation-based AMfrom users providing reviews for booksand exchanging opinions about these reviews to facilitate argumen-tative dialogue. The annotations amount to pairwise argumentativerelations ofattackandsupportbetween opinions and between opin-ions and reviews. As a result of the annotations, reviews and opinionsform structured debates which can be understood as bipolar argu-mentation frameworks. The platform also empowers annotationsof the same pairs by multiple annotators and can support differentmeasures of inter-annotator agreement and corpora selection
Quantum Thermalization With Couplings
We study the role of the system-bath coupling for the generalized canonical
thermalization [S. Popescu, et al., Nature Physics 2,754(2006) and S. Goldstein
et al., Phys. Rev. Lett. 96, 050403(2006)] that reduces almost all the pure
states of the "universe" [formed by a system S plus its surrounding heat bath
] to a canonical equilibrium state of S. We present an exactly solvable, but
universal model for this kinematic thermalization with an explicit
consideration about the energy shell deformation due to the interaction between
S and B. By calculating the state numbers of the "universe" and its subsystems
S and B in various deformed energy shells, it is found that, for the
overwhelming majority of the "universe" states (they are entangled at least),
the diagonal canonical typicality remains robust with respect to finite
interactions between S and B. Particularly, the kinematic decoherence is
utilized here to account for the vanishing of the off-diagonal elements of the
reduced density matrix of S. It is pointed out that the non-vanishing
off-diagonal elements due to the finiteness of bath and the stronger
system-bath interaction might offer more novelties of the quantum
thermalization.Comment: 4 pages, 2 figure
Lidar Remote Sensing for Characterizing Forest Vegetation - Special Issue. Foreword
The Silvilaser 2009 conference held in College Station, Texas, USA, was the ninth conference in the Silvilaser series, which started in 2002 with the international workshop on using lidar (Light Detection and Ranging) for analyzing forest structure, held in Victoria, British Columbia, Canada. Following the Canadian workshop, subsequent forestry-lidar conferences took place in Australia, Sweden, Germany, USA, Japan, Finland, and the United Kingdom (UK). By the time this Silvilaser 2009 special issue of PE&RS is published, the 10th international conference will have been held in Freiburg, Germany, and planning will be ongoing for the 11th meeting to take place in Tasmania, Australia, in October 2011. Papers presented at the 2005 conference held in Blacksburg, Virginia, USA, were assembled in a special issue of PE&RS published in December 2006. Other special issues resulting from previous conferences were published in journals such as the Canadian Journal of Remote Sensing (2003), the Scandinavian Journal of Forest Research (2004), and Japan s Journal of Forest Planning (2008). Given the conference history and the much longer record of publications on lidar applications for estimating forest biophysical parameters, which dates back to the early 1980s, we may consider lidar an established remote sensing technology for characterizing forest canopy structure and estimating forest biophysical parameters. Randy Wynne, a professor at Virginia Tech and the final keynote speaker at Silvilaser 2009, made the case that it was time to push 30 years of research into operations, along the lines of what has already been done to good effect in the Scandinavian countries. In Randy s words, it s time to "Just do it!" This special issue includes a selection of papers presented during the 2009 Silvilaser conference, which consisted of eight sections as follows: (1) biomass and carbon stock estimates, (2) tree species and forest type classification, (3) data fusion and integration, (4, 5, and 6) forest inventory, (7) silvicultural and ecological applications, and (8) terrestrial lidar applications. Within the constraint limiting the number of papers that could be fitted into the special issue we attempted to select those papers that best represented these conference topics and sections, giving special consideration to studies using forestry lidar data collected from each of the three platforms -- terrestrial, airborne, and spaceborne. Reflecting the international participation and reach of the conference, the studies presented here took place in the USA, Canada, Taiwan, the UK, and China
Application of AFLPs to characterize somaclonal variation in anther-derived grapevines
The AFLP (amplified fragment length polymorphism) technique was used to characterize genetic variation in grapevine (Vitis vinifera L.) regenerated from anther culture. 12 plants obtained by direct embryogenesis from cv. Valerien, and twelve plants obtained by indirect embryogenesis from cv. Mission were evaluated by AFLP. For each genotype the results were analyzed in comparison to control, represented by one field-grown plant (anther-donor). In contrast to cv. Mission, where no difference in polymorph pattern was observed in the DNA restricted with PstI/MseI, in cv. Valerien we found bands with different distribution among anther-derived plants and between them and the mother plant. When the DNA samples were digested with EcoRI in combination with methylation sensitive restriction enzymes MspI or HpaII, the AFLP products showed a higher polymorphism in cv. Mission with respect to the number of specific bands in correlation with the age of culture at the moment of regeneration from anthers. Direct embryogenesis from anther culture of cv. Valerien was associated with genetic variation induced in a very early stage of in vitro culture, while the indirect somatic embryogenesis, specific for cv. Mission and/or long-term culture was accompanied by changes in the methylation status. There is some evidence that all the analyzed grapevine somaclones regenerated from in vitro-cultured anthers are genetically distinct from the original cultivars.
Quantum privacy amplification and the security of quantum cryptography over noisy channels
Existing quantum cryptographic schemes are not, as they stand, operable in
the presence of noise on the quantum communication channel. Although they
become operable if they are supplemented by classical privacy-amplification
techniques, the resulting schemes are difficult to analyse and have not been
proved secure. We introduce the concept of quantum privacy amplification and a
cryptographic scheme incorporating it which is provably secure over a noisy
channel. The scheme uses an `entanglement purification' procedure which,
because it requires only a few quantum Controlled-Not and single-qubit
operations, could be implemented using technology that is currently being
developed. The scheme allows an arbitrarily small bound to be placed on the
information that any eavesdropper may extract from the encrypted message.Comment: 13 pages, Latex including 2 postcript files included using psfig
macro
The Crossover from Impurity to Valence Band in Diluted Magnetic Semiconductors: The Role of the Coulomb Attraction by Acceptor
The crossover between an impurity band (IB) and a valence band (VB) regime as
a function of the magnetic impurity concentration in models for diluted
magnetic semiconductors (DMS) is studied systematically by taking into
consideration the Coulomb attraction between the carriers and the magnetic
impurities. The density of states and the ferromagnetic transition temperature
of a Spin-Fermion model applied to DMS are evaluated using Dynamical Mean-Field
Theory (DMFT) and Monte Carlo (MC) calculations. It is shown that the addition
of a square-well-like attractive potential can generate an IB at small enough
Mn doping for values of the exchange that are not strong enough
to generate one by themselves. We observe that the IB merges with the VB when
where is a function of and the Coulomb attraction strength
. Using MC calculations, we demonstrate that the range of the Coulomb
attraction plays an important role. While the on-site attraction, that has been
used in previous numerical simulations, effectively renormalizes for all
values of , an unphysical result, a nearest-neighbor range attraction
renormalizes only at very low dopings, i.e., until the bound holes wave
functions start to overlap. Thus, our results indicate that the Coulomb
attraction can be neglected to study Mn doped GaSb, GaAs, and GaP in the
relevant doping regimes, but it should be included in the case of Mn doped GaN
that is expected to be in the IB regime.Comment: 8 pages, 4 Postscript figures, RevTex
Compositional characterisation of the Themis family
Context. It has recently been proposed that the surface composition of icy
main-belt asteroids (B-,C-,Cb-,Cg-,P-,and D-types) may be consistent with that
of chondritic porous interplanetary dust particles (CPIDPs). Aims. In the light
of this new association, we re-examine the surface composition of a sample of
asteroids belonging to the Themis family in order to place new constraints on
the formation and evolution of its parent body. Methods. We acquired NIR
spectral data for 15 members of the Themis family and complemented this dataset
with existing spectra in the visible and mid-infrared ranges to perform a
thorough analysis of the composition of the family. Assuming end-member
minerals and particle sizes (<2\mum) similar to those found in CPIDPs, we used
a radiative transfer code adapted for light scattering by small particles to
model the spectral properties of these asteroids. Results. Our best-matching
models indicate that most objects in our sample possess a surface composition
that is consistent with the composition of CP IDPs.We find ultra-fine grained
Fe-bearing olivine glasses to be among the dominant constituents. We further
detect the presence of minor fractions of Mg-rich crystalline silicates. The
few unsuccessfully matched asteroids may indicate the presence of interlopers
in the family or objects sampling a distinct compositional layer of the parent
body. Conclusions. The composition inferred for the Themis family members
suggests that the parent body accreted from a mixture of ice and anhydrous
silicates (mainly amorphous) and subsequently underwent limited heating. By
comparison with existing thermal models that assume a 400km diameter
progenitor, the accretion process of the Themis parent body must have occurred
relatively late (>4Myr after CAIs) so that only moderate internal heating
occurred in its interior, preventing aqueous alteration of the outer shell.Comment: 9 pages, 5 figures, accepted for publication in A&
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