22,925 research outputs found
How does breakup influence the total fusion of Li at the Coulomb barrier?
Total (complete + incomplete) fusion excitation functions of Li on
Co and Bi targets around the Coulomb barrier are obtained using
a new continuum discretized coupled channel (CDCC) method of calculating
fusion. The relative importance of breakup and bound-state structure effects on
total fusion is particularly investigated. The effect of breakup on fusion can
be observed in the total fusion excitation function. The breakup enhances the
total fusion at energies just around the barrier, whereas it hardly affects the
total fusion at energies well above the barrier. The difference between the
experimental total fusion cross sections for Li on Co is notably
caused by breakup, but this is not the case for the Bi target.Comment: 9 pages, 9 figures, Submitted to Phys. Rev.
Transient lateral photovoltaic effect in patterned metal-oxide-semiconductor films
The time dependent transient lateral photovoltaic effect has been studied
with us time resolution and with chopping frequencies in the kHz range, in
lithographically patterned 21 nm thick, 5, 10 and 20 um wide and 1500 um long
Co lines grown over naturally passivated p-type Si (100). We have observed a
nearly linear dependence of the transitorial response with the laser spot
position. A transitorial response with a sign change in the laser-off stage has
been corroborated by numerical simulations. A qualitative explanation suggests
a modification of the drift-diffusion model by including the in uence of a
local inductance. Our findings indicate that the microstructuring of position
sensitive detectors could improve their space-time resolution.Comment: 4 pages, 4 figure
Relating breakup and incomplete fusion of weakly-bound nuclei through a classical trajectory model with stochastic breakup
A classical dynamical model that treats break-up stochastically is presented
for low energy reactions of weakly-bound nuclei. The three-dimensional model
allows a consistent calculation of breakup, incomplete and complete fusion
cross sections. The model is assessed by comparing the breakup observables with
CDCC quantum mechanical predictions, which are found to be in reasonable
agreement. Through the model, it is demonstrated that the breakup probability
of the projectile as a function of its distance from the target is of primary
importance for understanding complete and incomplete fusion at energies near
the Coulomb barrier.Comment: Accepted in Physical Review Letter
Near-barrier Fusion Induced by Stable Weakly Bound and Exotic Halo Light Nuclei
The effect of breakup is investigated for the medium weight
Li+Co system in the vicinity of the Coulomb barrier. The strong
coupling of breakup/transfer channels to fusion is discussed within a
comparison of predictions of the Continuum Discretized Coupled-Channels model
which is also applied to He+Co a reaction induced by the borromean
halo nucleus He.Comment: 6 pages, 3 figures. A talk given at the FUSION06: International
Conference on Reaction Mechanisms and Nuclear Structure at the Coulomb
barrier, March 19-23, 2006, San Servolo, Venezia, Ital
The massive multiple system HD 64315
The O6 Vn star HD 64315 is believed to belong to the star-forming region
known as NGC 2467, but previous distance estimates do not support this
association. We explore the multiple nature of this star with the aim of
determining its distance, and understanding its connection to NGC 2467. A total
of 52 high-resolution spectra have been gathered over a decade. We use their
analysis, in combination with the photometric data from All Sky Automated
Survey and Hipparcos catalogues, to conclude that HD 64315 is composed of at
least two spectroscopic binaries, one of which is an eclipsing binary. HD 64315
contains two binary systems, one of which is an eclipsing binary. The two
binaries are separated by 0.09 arcsec (or 500 AU) if the most likely distance
to the system, around 5 kpc, is considered. The presence of fainter companions
is not excluded by current observations. The non-eclipsing binary (HD 64315
AaAb) has a period of 2.70962901+/-0.00000021 d. Its components are hotter than
those of the eclipsing binary, and dominate the appearance of the system. The
eclipsing binary (HD 64315 BaBb) has a shorter period of 1.0189569+/-0.0000008
d. We derive masses of 14.6+-2.3 M for both components of the BaBb
system. They are almost identical; both stars are overfilling their respective
Roche lobes, and share a common envelope in an overcontact configuration. The
non-eclipsing binary is a detached system composed of two stars with spectral
types around O6 V with minimum masses of 10.8 M and 10.2 M, and
likely masses aprox. 30 M. HD 64315 provides a cautionary tale about
high-mass star isolation and multiplicity. Its total mass is likely above 90
M,but it seems to have formed without an accompanying cluster. It
contains one the most massive overcontact binaries known, a likely merger
progenitor in a very wide multiple system.Comment: 14 pages, 13 figures, 8 Table
Active galactic nuclei synapses: X-ray versus optical classifications using artificial neural networks
(Abridged) Many classes of active galactic nuclei (AGN) have been defined
entirely throughout optical wavelengths while the X-ray spectra have been very
useful to investigate their inner regions. However, optical and X-ray results
show many discrepancies that have not been fully understood yet. The aim of
this paper is to study the "synapses" between the X-ray and optical
classifications.
For the first time, the new EFLUXER task allowed us to analyse broad band
X-ray spectra of emission line nuclei (ELN) without any prior spectral fitting
using artificial neural networks (ANNs). Our sample comprises 162 XMM-Newton/pn
spectra of 90 local ELN in the Palomar sample. It includes starbursts (SB),
transition objects (T2), LINERs (L1.8 and L2), and Seyferts (S1, S1.8, and S2).
The ANNs are 90% efficient at classifying the trained classes S1, S1.8, and
SB. The S1 and S1.8 classes show a wide range of S1- and S1.8-like components.
We suggest that this is related to a large degree of obscuration at X-rays. The
S1, S1.8, S2, L1.8, L2/T2/SB-AGN (SB with indications of AGN), and SB classes
have similar average X-ray spectra within each class, but these average spectra
can be distinguished from class to class. The S2 (L1.8) class is linked to the
S1.8 (S1) class with larger SB-like component than the S1.8 (S1) class. The L2,
T2, and SB-AGN classes conform a class in the X-rays similar to the S2 class
albeit with larger fractions of SB-like component. This SB-like component is
the contribution of the star-formation in the host galaxy, which is large when
the AGN is weak. An AGN-like component seems to be present in the vast majority
of the ELN, attending to the non-negligible fraction of S1-like or S1.8-like
component. This trained ANN could be used to infer optical properties from
X-ray spectra in surveys like eRosita.Comment: 15 pages, 7 figures, accepted for publication in A&A. Appendix B only
in the full version of the paper here:
https://dl.dropboxusercontent.com/u/3484086/AGNSynapsis_OGM_online.pd
Correlations between reflected and transmitted intensity patterns emerging from opaque disordered media
The propagation of monochromatic light through a scattering medium produces
speckle patterns in reflection and transmission, and the apparent randomness of
these patterns prevents direct imaging through thick turbid media. Yet, since
elastic multiple scattering is fundamentally a linear and deterministic
process, information is not lost but distributed among many degrees of freedom
that can be resolved and manipulated. Here we demonstrate experimentally that
the reflected and transmitted speckle patterns are correlated, even for opaque
media with thickness much larger than the transport mean free path, proving
that information survives the multiple scattering process and can be recovered.
The existence of mutual information between the two sides of a scattering
medium opens up new possibilities for the control of transmitted light without
any feedback from the target side, but using only information gathered from the
reflected speckle.Comment: 6 pages, 4 figure
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