25,697 research outputs found
Rotation in the ZAMS: Be and Bn stars
We show that Be stars belong to a high velocity tail of a single B-type star
rotational velocity distribution in the MS. This implies that: 1) the number
fraction N(Be)/N(Be+B) is independent of the mass; 2) Bn stars having ZAMS
rotational velocities higher than a given limit might become Be stars.Comment: 3 pages ; to appear in the proceedings of the Sapporo meeting on
active OB stars ; ASP Conference Series ; eds: S. Stefl, S. Owocki and A.
Okazak
Raman response of Stage-1 graphite intercalation compounds revisited
We present a detailed in-situ Raman analysis of stage-1 KC8, CaC6, and LiC6
graphite intercalation compounds (GIC) to unravel their intrinsic finger print.
Four main components were found between 1200 cm-1 and 1700 cm-1, and each of
them were assigned to a corresponding vibrational mode. From a detailed line
shape analysis of the intrinsic Fano-lines of the G- and D-line response we
precisely determine the position ({\omega}ph), line width ({\Gamma}ph) and
asymmetry (q) from each component. The comparison to the theoretical calculated
line width and position of each component allow us to extract the
electron-phonon coupling constant of these compounds. A coupling constant
{\lambda}ph < 0.06 was obtained. This highlights that Raman active modes alone
are not sufficient to explain the superconductivity within the electron-phonon
coupling mechanism in CaC6 and KC8.Comment: 6 pages, 3 figures, 2 table
Graph theoretical structures in logic programs and default theories
In this paper we present a graph representation of logic programs and default theories. We show that many of the semantics proposed for logic programs can be expressed in terms of notions emerging from graph theory, establishing in this way a link between the fields. Namely the stable models, the partial stable models, and the well-founded semantics correspond respectively to the kernels, semikernels and the initial acyclic part of the associated graph. This link allows us to consider both theoretical problems (existence, uniqueness) and computational problems (tractability, algorithms, approximations) from a more abstract and rather combinatorial point of view. It also provides a clear and intuitive understanding about how conflicts between rules are resolved within the different semantics. Furthermore, we extend the basic framework developed for logic programs to the case of Default Logic by introducing the notions of partial, deterministic and well-founded extensions for default theories. These semantics capture different ways of reasoning with a default theory
Spin interference and Fano effect in electron transport through a mesoscopic ring side-coupled with a quantum dot
We investigate the electron transport through a mesoscopic ring side-coupled
with a quantum dot(QD) in the presence of Rashba spin-orbit(SO) interaction. It
is shown that both the Fano resonance and the spin interference effects play
important roles in the electron transport properties. As the QD level is around
the Fermi energy, the total conductance shows typical Fano resonance line
shape. By applying an electrical gate voltage to the QD, the total transmission
through the system can be strongly modulated. By threading the mesoscopic ring
with a magnetic flux, the time-reversal symmetry of the system is broken, and a
spin polarized current can be obtained even though the incident current is
unpolarized.Comment: 5 pages, 5 figure
Three-body hadron systems with strangeness
Recently, many efforts are being put in studying three-hadron systems made of
mesons and baryons and interesting results are being found. In this talk, I
summarize the main features of the formalism used to study such three hadron
systems with strangeness within a framework built on the basis of
unitary chiral theories and solution of the Faddeev equations. In particular, I
present the results obtained for the , and
systems and their respective coupled channels. In the first case, we find four
's and two 's with spin-parity , in the 1500-1800
MeV region, as two meson-one baryon s-wave resonances. In the second case, a
around 1900 MeV is found. For the last one a kaon close to 1420
MeV is formed, which can be identified with K(1460).Comment: Proceeding written for the HYP2012 conferenc
High Spectral and Spatial Resolution Observations of the PDR Emission in the NGC2023 Reflection Nebula with SOFIA and APEX
We have mapped the NGC 2023 reflection nebula in [CII] and CO(11--10) with
the heterodyne receiver GREAT on SOFIA and obtained slightly smaller maps in
13CO(3--2), CO(3--2), CO(4--3), CO(6--5), and CO(7--6) with APEX in Chile. We
use these data to probe the morphology, kinematics, and physical conditions of
the C II region, which is ionized by FUV radiation from the B2 star HD37903.
The [CII] emission traces an ellipsoidal shell-like region at a position angle
of ~ -50 deg, and is surrounded by a hot molecular shell. In the southeast,
where the C II region expands into a dense, clumpy molecular cloud ridge, we
see narrow and strong line emission from high-J CO lines, which comes from a
thin, hot molecular shell surrounding the [CII] emission. The [CII] lines are
broader and show photo evaporating gas flowing into the C II region. Based on
the strength of the [13CII] F=2--1 line, the [CII] line appears to be somewhat
optically thick over most of the nebula with an optical depth of a few. We
model the physical conditions of the surrounding molecular cloud and the PDR
emission using both RADEX and simple PDR models. The temperature of the CO
emitting PDR shell is ~ 90 -- 120 K, with densities of 10^5 -- 10^6 cm^-3, as
deduced from RADEX modeling. Our PDR modeling indicates that the PDR layer
where [CII] emission dominates has somewhat lower densities, 10^4 to a few
times 10^5 cm^-3Comment: Accepted by A&
Boson stars in massive dilatonic gravity
We study equilibrium configurations of boson stars in the framework of a
class scalar-tensor theories of gravity with massive gravitational scalar
(dilaton). In particular we investigate the influence of the mass of the
dilaton on the boson star structure. We find that the masses of the boson stars
in presence of dilaton are close to those in general relativity and they are
sensitive to the ratio of the boson mass to the dilaton mass within a typical
few percent. It turns out also that the boson star structure is mainly
sensitive to the mass term of the dilaton potential rather to the exact form of
the potential.Comment: 9 pages, latex, 9 figures, one figure dropped, new comments added,
new references added, typos correcte
Probing the electron-phonon coupling in ozone-doped graphene by Raman spectroscopy
We have investigated the effects of ozone treatment on graphene by Raman
scattering. Sequential ozone short-exposure cycles resulted in increasing the
doping levels as inferred from the blue shift of the 2 and peak
frequencies, without introducing significant disorder. The two-phonon 2 and
2 Raman peak intensities show a significant decrease, while, on the
contrary, the one-phonon G Raman peak intensity remains constant for the whole
exposure process. The former reflects the dynamics of the photoexcited
electrons (holes) and, specifically, the increase of the electron-electron
scattering rate with doping. From the ratio of 2 to 2 intensities, which
remains constant with doping, we could extract the ratio of electron-phonon
coupling parameters. This ratio is found independent on the number of layers up
to ten layers. Moreover, the rate of decrease of 2 and 2 intensities
with doping was found to slowdown inversely proportional to the number of
graphene layers, revealing the increase of the electron-electron collision
probability
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