9,442 research outputs found
Neutron Transfer Dynamics and Doorway to Fusion in Time-Dependent Hartree-Fock Theory
We analyze the details of mass exchange in the vicinity of the Coulomb
barrier for heavy-ion collisions involving neutron-rich nuclei using the
time-dependent Hartree-Fock (TDHF) theory. We discuss the time-dependence of
transfer and show that the potential barriers seen by individual
single-particle states can be considerably different than the effective barrier
for the two interacting nuclei having a single center-of-mass. For this reason
we observe a substantial transfer probability even at energies below the
effective barrier.Comment: 6 pages, 9 figure
Probing onset of strong localization and electron-electron interactions with the presence of direct insulator-quantum Hall transition
We have performed low-temperature transport measurements on a disordered
two-dimensional electron system (2DES). Features of the strong localization
leading to the quantum Hall effect are observed after the 2DES undergoes a
direct insulator-quantum Hall transition with increasing the perpendicular
magnetic field. However, such a transition does not correspond to the onset of
strong localization. The temperature dependences of the Hall resistivity and
Hall conductivity reveal the importance of the electron-electron interaction
effects to the observed transition in our study.Comment: 9 pages, 4 figure
IMAGES II. A surprisingly low fraction of undisturbed rotating spiral disks at z~0.6: The morpho-kinematical relation 6 Gyrs ago
We present a first combined analysis of the morphological and dynamical
properties for the Intermediate MAss Galaxy Evolution Sequence (IMAGES) sample.
It is a representative sample of 52 z~0.6 galaxies with Mstell from 1.5 to 15
10^10Msun and possessing 3D resolved kinematics and HST deep imaging in at
least two broad band filters. We aim at evaluate robustly the evolution of
rotating spirals since z~0.6, as well as to test the different schemes for
classifying galaxies morphologically. We used all the information provided by
multi-band images, color maps and 2 dimensional light fitting to assign to each
object a morphological class. We divided our sample between spiral disks,
peculiar objects, compact objects and mergers. Using our morphological
classification scheme, 4/5 of identified spirals are rotating disks and more
than 4/5 of identified peculiar galaxies show complex kinematics, while
automatic classification methods such as Concentration-Asymmetry and GINI-M20
severely overestimate the fraction of relaxed disk galaxies. Using this
methodology, we find that the fraction of rotating spirals has increased by a
factor ~ 2 during the last 6 Gyrs, a much higher fraction that found previously
based on morphologies alone. These rotating spiral disks are forming stars very
rapidly, doubling their stellar masses over the last 6 Gyrs, while most of
their stars have been formed few Gyrs earlier, which reveals the presence of a
large gas supply. Because they are likely the progenitors of local spirals, we
can conjecture how their properties are evolving. Their disks show some
evidence for an inside-out growth and the gas supply/accretion is not made
randomly as the disk need to be stable in order to match the local disk
properties.Comment: Typos corrected, reference adde
Near-barrier Fusion and Breakup/Transfer induced by Weakly Bound and Exotic Halo Nuclei
The influence on the fusion process of coupling to collective degrees of
freedom has been explored. The significant enhancement of the fusion cross
section at sub-barrier energies was compared to predictions of one-dimensional
barrier penetration models. This was understood in terms of the dynamical
processes arising from strong couplings to collective inelastic excitations of
the target and projectile. However, in the case of reactions where at least one
of the colliding nuclei has a sufficiently low binding energy, for breakup to
become an important process, conflicting model predictions and experimental
results have been reported in the literature. Excitation functions for sub- and
near-barrier total (complete + incomplete) fusion cross sections have been
measured for the Li+Co reactions. Elastic scattering as well as
breakup/transfer yields have also been measured at several incident energies.
Results of Continuum-Discretized Coupled-Channel ({\sc Cdcc}) calculations
describe reasonably well the experimental data for both reactions at and above
the barrier. A systematic study of He induced fusion reactions with a
three-body {\sc Cdcc} method is presented. The relative importance of breakup
and bound-state structure effects on total fusion (excitation functions) is
particularly investigated. The four-body {\sc Cdcc} model is being currently
developed.Comment: 8 pages, 3 figures; espcrc1 style; Invited Talk given at IX Int.Conf.
on Nucleus-Nucleus Collisions, Rio de Janeiro Aug.2006; submitted to
Nucl.Phys.
Images IV: Strong evolution of the oxygen abundance in gaseous phases of intermediate mass galaxies since z=0.8
Intermediate mass galaxies (logM(Msun)>10) at z~0.6 are the likeliest
progenitors of the present-day numerous population of spirals. There is growing
evidence that they have evolved rapidly since the last 6 to 8 Gyr ago, and
likely have formed a significant fraction of their stellar mass, often showing
perturbed morphologies and kinematics. We have gathered a representative sample
of 88 such galaxies and have provided robust estimates of their gas phase
metallicity. For doing so, we have used moderate spectral resolution
spectroscopy at VLT/FORS2 with unprecedented high S/N allowing to remove biases
coming from interstellar absorption lines and extinction to establish robust
values of R23=([OII]3727 + [OIII]4959,5007)/Hbeta. We definitively confirm that
the predominant population of z~0.6 starbursts and luminous IR galaxies (LIRGs)
are on average, two times less metal rich than the local galaxies at a given
stellar mass. We do find that the metal abundance of the gaseous phase of
galaxies is evolving linearly with time, from z=1 to z=0 and after comparing
with other studies, from z=3 to z=0. Combining our results with the reported
evolution of the Tully Fisher relation, we do find that such an evolution
requires that ~30% of the stellar mass of local galaxies have been formed
through an external supply of gas, thus excluding the close box model. Distant
starbursts & LIRGs have properties (metal abundance, star formation efficiency
& morphologies) similar to those of local LIRGs. Their underlying physics is
likely dominated by gas infall probably through merging or interactions. Our
study further supports the rapid evolution of z~0.4-1 galaxies. Gas exchanges
between galaxies is likely the main cause of this evolution.Comment: 21 pages, 12 figures, A&A, In pres
Modeling transport through single-molecule junctions
Non-equilibrium Green's functions (NEGF) formalism combined with extended
Huckel (EHT) and charging model are used to study electrical conduction through
single-molecule junctions. Analyzed molecular complex is composed of asymmetric
1,4-Bis((2'-para-mercaptophenyl)-ethinyl)-2-acetyl-amino-5-nitro-benzene
molecule symmetrically coupled to two gold electrodes [Reichert et al., Phys.
Rev. Lett. Vol.88 (2002), pp. 176804]. Owing to this model, the accurate values
of the current flowing through such junction can be obtained by utilizing basic
fundamentals and coherently deriving model parameters. Furthermore, the
influence of the charging effect on the transport characteristics is
emphasized. In particular, charging-induced reduction of conductance gap,
charging-induced rectification effect and charging-generated negative value of
the second derivative of the current with respect to voltage are observed and
examined for molecular complex.Comment: 8 pages, 3 figure
IMAGES I. Strong evolution of galaxy kinematics since z=1
(abbreviated) We present the first results of the ESO large program,
``IMAGES'' which aims at obtaining robust measurements of the kinematics of
distant galaxies using the multi-IFU mode of GIRAFFE on the VLT. 3D
spectroscopy is essential to robustly measure the often distorted kinematics of
distant galaxies (e.g., Flores et al. 2006). We derive the velocity fields and
-maps of 36 galaxies at 0.4<z<0.75 from the kinematics of the [OII]
emission line doublet, and generate a robust technique to identify the nature
of the velocity fields based on the pixels of the highest signal-to-noise
ratios (S/N). We have gathered a unique sample of 63 velocity fields of
emission line galaxies (W0([OII]) > 15 A) at z=0.4-0.75, which are a
representative subsample of the population of M_stellar>1.5x10^{10} M_sun
emission line galaxies in this redshift range, and are largely unaffected by
cosmic variance. Taking into account all galaxies -with or without emission
lines- in that redshift range, we find that at least 41+/-7% of them have
anomalous kinematics, i.e., they are not dynamically relaxed. This includes
26+/-7% of distant galaxies with complex kinematics, i.e., they are not simply
pressure or rotationally supported. Our result implies that galaxy kinematics
are among the most rapidly evolving properties, because locally, only a few
percent of the galaxies in this mass range have complex kinematics.Comment: 17 pages, 6 figures, Accepted by A&
Cosmological Models and Latest Observational Data
In this note, we consider the observational constraints on some cosmological
models by using the 307 Union type Ia supernovae (SNIa), the 32 calibrated
Gamma-Ray Bursts (GRBs) at , the updated shift parameter from WMAP
5-year data (WMAP5), and the distance parameter of the measurement of the
baryon acoustic oscillation (BAO) peak in the distribution of SDSS luminous red
galaxies with the updated scalar spectral index from WMAP5. The tighter
constraints obtained here update the ones obtained previously in the
literature.Comment: 10 pages, 5 figures, 1 table, revtex4; v2: discussions added,
accepted by Eur. Phys. J. C; v3: published versio
531 new spectroscopic redshifts from the CDFS and a test on the cosmological relevance of the GOODS-South field
(Abbrev.) This paper prepares a series of papers analysing the Intermediate
MAss Galaxy Evolution Sequence (IMAGES) up to z=1. Intermediate mass galaxies
(MJ <=-20.3) are selected from the Chandra Deep Field South (CDFS) for which we
identify a serious lack of spectroscopically determined redshifts..... We have
spectroscopically identified 691 objects including 580 gal., 7 QSOs, and 104
stars. This study provides 531 new redshifts in the CDFS. It confirms the
presence of several large scale structures in the CDFS. To test the impact of
these structures in the GOODS-South field, we ... compare the evolution of
rest-frame U, B, V and K galaxy luminosity densities to that derived from the
CFRS. The CDFS field shows a significant excess of luminosity densities in the
z=0.5-0.75 range, which increases with the wavelength, reaching up to 0.5 dex
at 2.1 um. Stellar mass and specific star formation evolutions might be
significantly affected by the presence of the peculiar large scale structures
at z= 0.668 and at z= 0.735, that contain a significant excess of evolved,
massive galaxies when compared to other fields. This leads to a clear warning
to results based on the CDFS/GOODS South fields, especially those related to
the evolution of red luminosity densities, i.e. stellar mass density and
specific star formation rate. Photometric redshift techniques, when applied to
that field, are producing quantities which are apparently less affected by
cosmic variance (0.25 dex at 2.1 um), however at the cost of the difficulty in
disentangling between evolutionary and cosmic variance effects.Comment: Accepted for publication in A&A, 19 pages, 13 figure
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