6,091 research outputs found
Mechanisms for Direct Breakup Reactions
We review some simple mechanisms of breakup in nuclear reactions. We mention
the spectator breakup, which is described in the post-form DWBA. The relation
to other formulations is also indicated. An especially important mechanism is
Coulomb dissociation. It is a distinct advantage that the perturbation due to
the electric field of the nucleus is exactly known. Therefore firm conclusions
can be drawn from such measurements. Some new applications of Coulomb
dissociation for nuclear astrophysics are discussed.Comment: 17 pages, 5 figures, to appear in the proceedings of the RCNP-TMU
Symposium on Spins in Nuclear and Hadronic Reactions, October 16-18 199
A planetary eclipse map of CoRoT-2a. Comprehensive lightcurve modeling combining rotational-modulation and transits
We analyze the surface structure of the planet host star CoRoT-2a using a
consistent model for both the `global' (i.e., rotationally modulated)
lightcurve and the transit lightcurves, using data provided by the CoRoT
mission. Selecting a time interval covering two stellar rotations and six
transits of the planetary companion CoRoT-2b, we adopt a `strip' model of the
surface to reproduce the photometric modulation inside and outside the transits
simultaneously. Our reconstructions show that it is possible to achieve
appropriate fits for the entire sub-interval using a low-resolution surface
model with 36 strips. The surface reconstructions indicate that the brightness
on the eclipsed section of the stellar surface is (6 +/- 1) % lower than the
average brightness of the remaining surface. This result suggests a
concentration of stellar activity in a band around the stellar equator similar
to the behavior observed on the Sun.Comment: accepted by A&A on 12/09/200
Spectral observations of X Persei: Connection between H-alpha and X-ray emission
We present spectroscopic observations of the Be/X-ray binary X Per obtained
during the period 1999 - 2018. Using new and published data, we found that
during "disc-rise" the expansion velocity of the circumstellar disc is 0.4 -
0.7 km/s. Our results suggest that the disc radius in recent decades show
evidence of resonant truncation of the disc by resonances 10:1, 3:1, and 2:1,
while the maximum disc size is larger than the Roche lobe of the primary and
smaller than the closest approach of the neutron star. We find correlation
between equivalent width of H-alpha emission line () and the X-ray
flux, which is visible when . The
correlation is probably due to wind Roche lobe overflow.Comment: Accepted for publication in Astronomy & Astrophysic
Planetary eclipse mapping of CoRoT-2a. Evolution, differential rotation, and spot migration
The lightcurve of CoRoT-2 shows substantial rotational modulation and
deformations of the planet's transit profiles caused by starspots. We
consistently model the entire lightcurve, including both rotational modulation
and transits, stretching over approximately 30 stellar rotations and 79
transits. The spot distribution and its evolution on the noneclipsed and
eclipsed surface sections are presented and analyzed, making use of the high
resolution achievable under the transit path.
We measure the average surface brightness on the eclipsed section to be
(5\pm1) % lower than on the noneclipsed section. Adopting a solar spot
contrast, the spot coverage on the entire surface reaches up to 19 % and a
maximum of almost 40 % on the eclipsed section. Features under the transit
path, i.e. close to the equator, rotate with a period close to 4.55 days.
Significantly higher rotation periods are found for features on the noneclipsed
section indicating a differential rotation of . Spotted
and unspotted regions in both surface sections concentrate on preferred
longitudes separated by roughly 180 deg.Comment: Paper accepted by A&A 17/02/2010. For a better resolution paper
please visit my homepage:
http://www.hs.uni-hamburg.de/EN/Ins/Per/Huber/index.htm
Mimicry and ultrastructural analogy between the semi-aquatic grasshopper Paulinia acuminata (Orthoptera: Pauliniidae) and its foodplant, the water-fern Salvinia auriculata (Filicatae: Salviniaceae)
The semi-aquatic grasshopper Paulinia acuminata is mimetically protected by a striking similarity to its foodplant, the floating fern Salvinia auriculata. A SEM study of the cuticula of young grasshopper nymphs and the Salvinia leaf surface reveals a similar ultrastructure of epicuticular waxes which makes both organisms extremely water repellent
Religiosity and Sexual Risk Behaviors Among Latina Adolescents: Trends from 1995 to 2008
Purpose: The purpose of this study was to determine trends in the influence of religiosity on sexual activity of Latina adolescents in the United States from 1995 to 2008 and to determine if differences existed between the Mexican American and other Latina groups.
Methods: The sample comprised the subset of unmarried, 15–21-year-old (mean 17 years) Latina female respondents in the 1995 (n=267), 2002 (n=306), and 2006–2008 (n=400) National Survey of Family Growth (NSFG) datasets. Associations between religiosity (importance of religion and service attendance) and history of ever having sex, number of sex partners, and age of sexual debut were investigated.
Results: Less than one half of Latinas in 1995 (44%) and in 2006–2008 (44%) reported that religion was very important to them, whereas in 2002, 50% reported it was important. Only in 1995 did Latinas who viewed religion as very important have a significantly lower level of sexual initiation. In 1995 and in 2006–2008, Latinas who held religion as very important had significantly fewer partners. In all three cohorts, the higher religious importance group had higher virgin survival rates. Across cohorts, approximately one third of respondents reported frequent religious attendance. In all cohorts, frequent attenders were less likely to have had sex, had fewer partners, and had older age at sexual debut. The survival rate as virgins for Mexican origin Latinas was higher in 1995 and 2002 compared to non-Mexican Latinas but was almost the same in 2006–2008.
Conclusions: Religiosity had a protective association with sexual activity among Latina adolescents. The association of importance of religion with sexual activity has diminished from 1995 to 2008, however, whereas the importance of service attendance has remained stable. The influence of religion was more apparent among the Latinas of Mexican origin, but this greater influence also diminished by 2006–2008
Fishtail effect and vortex dynamics in LiFeAs single crystals
We investigate the fishtail effect, critical current density () and
vortex dynamics in LiFeAs single crystals. The sample exhibits a second peak
(SP) in the magnetization loop only with the field c-axis. We calculate a
reasonably high , however, values are lower than in 'Ba-122' and
'1111'-type FeAs-compounds. Magnetic relaxation data imply a strong pinning
which appears not to be due to conventional defects. Instead, its behavior is
similar to that of the triplet superconductor SrRuO. Our data suggest
that the origin of the SP may be related to a vortex lattice phase transition.
We have constructed the vortex phase diagram for LiFeAs on the
field-temperature plane.Comment: 5 pages, 5 figure
Le degre d'interdependance internationale des prix en France et en Italie = The degree of international interdependence affecting prices in France and in Italy. II/367/1/72-F, May 1972
Pairing correlations in N~Z pf-shell nuclei
We perform Shell Model Monte Carlo calculations to study pair correlations in
the ground states of nuclei with masses A=48-60. We find that ,
proton-neutron correlations play an important, and even dominant
role, in the ground states of odd-odd nuclei, in agreement with
experiment. By studying pairing in the ground states of Fe, we
observe that the isovector proton-neutron correlations decrease rapidly with
increasing neutron excess. In contrast, both the proton, and trivially the
neutron correlations increase as neutrons are added.
We also study the thermal properties and the temperature dependence of pair
correlations for Mn and Fe as exemplars of odd-odd and even-even
nuclei. While for Fe results are similar to those obtained for
other even-even nuclei in this mass range, the properties of Mn at low
temperatures are strongly influenced by isovector neutron-proton pairing. In
coexistence with these isovector pair correlations, our calculations also
indicate an excess of isoscalar proton-neutron pairing over the mean-field
values. The isovector neutron-proton correlations rapidly decrease with
temperatures and vanish for temperatures above keV, while the isovector
correlations among like nucleons persist to higher temperatures. Related to the
quenching of the isovector proton-neutron correlations, the average isospin
decreases from 1, appropriate for the ground state, to 0 as the temperature
increases
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