523 research outputs found
Full counting statistics for transport through a molecular quantum dot magnet
Full counting statistics (FCS) for the transport through a molecular quantum
dot magnet is studied theoretically in the incoherent tunneling regime. We
consider a model describing a single-level quantum dot, magnetically coupled to
an additional local spin, the latter representing the total molecular spin s.
We also assume that the system is in the strong Coulomb blockade regime, i.e.,
double occupancy on the dot is forbidden. The master equation approach to FCS
introduced in Ref. [12] is applied to derive a generating function yielding the
FCS of charge and current. In the master equation approach, Clebsch-Gordan
coefficients appear in the transition probabilities, whereas the derivation of
generating function reduces to solving the eigenvalue problem of a modified
master equation with counting fields. To be more specific, one needs only the
eigenstate which collapses smoothly to the zero-eigenvalue stationary state in
the limit of vanishing counting fields. We discovered that in our problem with
arbitrary spin s, some quartic relations among Clebsch-Gordan coefficients
allow us to identify the desired eigenspace without solving the whole problem.
Thus we find analytically the FCS generating function in the following two
cases: i) both spin sectors lying in the bias window, ii) only one of such spin
sectors lying in the bias window. Based on the obtained analytic expressions,
we also developed a numerical analysis in order to perform a similar
contour-plot of the joint charge-current distribution function, which have
recently been introduced in Ref. [13], here in the case of molecular quantum
dot magnet problem.Comment: 17 pages, 5 figure
Full counting statistics of information content
We review connections between the cumulant generating function of full
counting statistics of particle number and the R\'enyi entanglement entropy. We
calculate these quantities based on the fermionic and bosonic path-integral
defined on multiple Keldysh contours. We relate the R\'enyi entropy with the
information generating function, from which the probability distribution
function of self-information is obtained in the nonequilibrium steady state. By
exploiting the distribution, we analyze the information content carried by a
single bosonic particle through a narrow-band quantum communication channel.
The ratio of the self-information content to the number of bosons fluctuates.
For a small boson occupation number, the average and the fluctuation of the
ratio are enhanced.Comment: 16 pages, 5 figure
Состояние плазменного гемостаза и морфометрических параметров тромбоцитов при плацентарной недостаточности
БЕРЕМЕННОСТЬПЛАЦЕНТАРНАЯ НЕДОСТАТОЧНОСТЬТРОМБОЦИТЫГЕМОСТА
Correlation effects and the high-frequency spin susceptibility of an electron liquid: Exact limits
Spin correlations in an interacting electron liquid are studied in the
high-frequency limit and in both two and three dimensions. The third-moment sum
rule is evaluated and used to derive exact limiting forms (at both long- and
short-wavelengths) for the spin-antisymmetric local-field factor, . In two dimensions is found to diverge as at long wavelengths,
and the spin-antisymmetric exchange-correlation kernel of time-dependent spin
density functional theory diverges as in both two and three dimensions.
These signal a failure of the local-density approximation, one that can be
redressed by alternative approaches.Comment: 5 page
Fermi-surface reconstruction involving two Van Hove singularities across the antiferromagnetic transition in BaFe2As2
We report an angle-resolved photoemission study of BaFe2As2, a parent
compound of iron-based superconductors. Low-energy tunable excitation photons
have allowed the first observation of a saddle-point singularity at the Z
point, as well as the Gamma point. With antiferromagnetic ordering, both of
these two van Hove singularities come down below the Fermi energy, leading to a
topological change in the innermost Fermi surface around the kz axis from
cylindrical to tear-shaped, as expected from first-principles calculation.
These singularities may provide an additional instability for the Fermi surface
of the superconductors derived from BaFe2As2.Comment: 14 pages, 4 figures, 1 tabl
Overdensities of Y-dropout Galaxies from the Brightest-of-Reionizing Galaxies Survey: A Candidate Protocluster at Redshift z~8
Theoretical and numerical modeling of dark-matter halo assembly predicts that
the most luminous galaxies at high redshift are surrounded by overdensities of
fainter companions. We test this prediction with HST observations acquired by
our Brightest of Reionizing Galaxies (BoRG) survey, which identified four very
bright z~8 candidates as Y-dropout sources in four of the 23 non-contiguous
WFC3 fields observed. We extend here the search for Y-dropouts to fainter
luminosities (M_* galaxies with M_AB\sim-20), with detections at >5sigma
confidence (compared to >8sigma confidence adopted earlier) identifying 17 new
candidates. We demonstrate that there is a correlation between number counts of
faint and bright Y-dropouts at >99.84% confidence. Field BoRG58, which contains
the best bright z\sim8 candidate (M_AB=-21.3), has the most significant
overdensity of faint Y-dropouts. Four new sources are located within 70arcsec
(corresponding to 3.1 comoving Mpc at z=8) from the previously known brighter
z\sim8 candidate. The overdensity of Y-dropouts in this field has a physical
origin to high confidence (p>99.975%), independent of completeness and
contamination rate of the Y-dropout selection. We modeled the overdensity by
means of cosmological simulations and estimate that the principal dark matter
halo has mass M_h\sim(4-7)x10^11Msun (\sim5sigma density peak) and is
surrounded by several M_h\sim10^11Msun halos which could host the fainter
dropouts. In this scenario, we predict that all halos will eventually merge
into a M_h>2x10^14Msun galaxy cluster by z=0. Follow-up observations with
ground and space based telescopes are required to secure the z\sim8 nature of
the overdensity, discover new members, and measure their precise redshift.Comment: Minor revision: ApJ accepted [17 pages (emulateapj style), 7 figures,
2 tables
Residual Kondo effect in quantum dot coupled to half-metallic ferromagnets
We study the Kondo effect in a quantum dot coupled to half-metallic
ferromagnetic electrodes in the regime of strong on-dot correlations. Using the
equation of motion technique for nonequilibrium Green functions in the slave
boson representation we show that the Kondo effect is not completely suppressed
for anti-parallel leads magnetization. In the parallel configuration there is
no Kondo effect but there is an effect associated with elastic cotunneling
which in turn leads to similar behavior of the local (on-dot) density of states
(LDOS) as the usual Kondo effect. Namely, the LDOS shows the temperature
dependent resonance at the Fermi energy which splits with the bias voltage and
the magnetic field. Moreover, unlike for non-magnetic or not fully polarized
ferromagnetic leads the only minority spin electrons can form such resonance in
the density of states. However, this resonance cannot be observed directly in
the transport measurements and we give some clues how to identify the effect in
such systems.Comment: 15 pages, 8 figures, accepted for publication in J. Phys.: Condens.
Mat
s-Process Nucleosynthesis in Carbon Stars
We present the first detailed and homogeneous analysis of the s-element
content in Galactic carbon stars of N-type. Abundances of Sr,Y, Zr (low-mass
s-elements, or ls) and of Ba, La, Nd, Sm and Ce (high-mass s-elements, hs) are
derived using the spectral synthesis technique from high-resolution spectra.
The N-stars analyzed are of nearly solar metallicity and show moderate
s-element enhancements, similar to those found in S stars, but smaller than
those found in the only previous similar study (Utsumi 1985), and also smaller
than those found in supergiant post-AGB stars. This is in agreement with the
present understanding of the envelope s-element enrichment in giant stars,
which is increasing along the spectral sequence M-->MS-->S-->SC-->C during the
AGB phase. We compare the observational data with recent -process
nucleosynthesis models for different metallicities and stellar masses. Good
agreement is obtained between low mass AGB star models (M < 3 M_o) and
s-elements observations. In low mass AGB stars, the 13C(alpha, n)16O reaction
is the main source of neutrons for the s-process; a moderate spread, however,
must exist in the abundance of 13C that is burnt in different stars. By
combining information deriving from the detection of Tc, the infrared colours
and the theoretical relations between stellar mass, metallicity and the final
C/O ratio, we conclude that most (or maybe all) of the N-stars studied in this
work are intrinsic, thermally-pulsing AGB stars; their abundances are the
consequence of the operation of third dredge-up and are not to be ascribed to
mass transfer in binary systems.Comment: 31 pages, 10 figures, 6 tables. Accepted in Ap
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