194 research outputs found
Macroscopic dynamics of the fusion process
A macroscopic dynamical model has been used to calculate fusion cross sections for a wide number of systems ranging from 16O + 27Al to 40Ar + 165Ho. This model takes into account the reorganization of the densities and the nucleon exchanges. The possible reaction mechanisms after capture of the system into the pocket of the interaction potential are discussed Two processes contribute to fusion : compound nucleus formation and fast fission phenomenon. The calculated fusion cross sections are in overall agreement with the data
Breakup Conditions of Projectile Spectators from Dynamical Observables
Momenta and masses of heavy projectile fragments (Z >= 8), produced in
collisions of 197Au with C, Al, Cu and Pb targets at E/A = 600 MeV, were
determined with the ALADIN magnetic spectrometer at SIS. An analysis of
kinematic correlations between the two and three heaviest projectile fragments
in their rest frame was performed. The sensitivity of these correlations to the
conditions at breakup was verified within the schematic SOS-model. The data
were compared to calculations with statistical multifragmentation models and to
classical three-body calculations. Classical trajectory calculations reproduce
the dynamical observables. The deduced breakup parameters, however, differ
considerably from those assumed in the statistical multifragmentation models
which describe the charge correlations. If, on the other hand, the analysis of
kinematic and charge correlations is performed for events with two and three
heavy fragments produced by statistical multifragmentation codes, a good
agreement with the data is found with the exception that the fluctuation widths
of the intrinsic fragment energies are significantly underestimated. A new
version of the multifragmentation code MCFRAG was therefore used to investigate
the potential role of angular momentum at the breakup stage. If a mean angular
momentum of 0.75/nucleon is added to the system, the energy fluctuations
can be reproduced, but at the same time the charge partitions are modified and
deviate from the data.
PACS numbers: 25.70.Mn, 25.70.Pq, 25.75.Ld, 25.75.-qComment: 38 pages, RevTeX with 21 included figures; Also available from
http://www-kp3.gsi.de/www/kp3/aladin_publications.htm
Poisson-Jacobi reduction of homogeneous tensors
The notion of homogeneous tensors is discussed. We show that there is a
one-to-one correspondence between multivector fields on a manifold ,
homogeneous with respect to a vector field on , and first-order
polydifferential operators on a closed submanifold of codimension 1 such
that is transversal to . This correspondence relates the
Schouten-Nijenhuis bracket of multivector fields on to the Schouten-Jacobi
bracket of first-order polydifferential operators on and generalizes the
Poissonization of Jacobi manifolds. Actually, it can be viewed as a
super-Poissonization. This procedure of passing from a homogeneous multivector
field to a first-order polydifferential operator can be also understood as a
sort of reduction; in the standard case -- a half of a Poisson reduction. A
dual version of the above correspondence yields in particular the
correspondence between -homogeneous symplectic structures on and
contact structures on .Comment: 19 pages, minor corrections, final version to appear in J. Phys. A:
Math. Ge
Nuclear fission: The "onset of dissipation" from a microscopic point of view
Semi-analytical expressions are suggested for the temperature dependence of
those combinations of transport coefficients which govern the fission process.
This is based on experience with numerical calculations within the linear
response approach and the locally harmonic approximation. A reduced version of
the latter is seen to comply with Kramers' simplified picture of fission. It is
argued that for variable inertia his formula has to be generalized, as already
required by the need that for overdamped motion the inertia must not appear at
all. This situation may already occur above T=2 MeV, where the rate is
determined by the Smoluchowski equation. Consequently, comparison with
experimental results do not give information on the effective damping rate, as
often claimed, but on a special combination of local stiffnesses and the
friction coefficient calculated at the barrier.Comment: 31 pages, LaTex, 9 postscript figures; final, more concise version,
accepted for publication in PRC, with new arguments about the T-dependence of
the inertia; e-mail: [email protected]
The systematic study of the influence of neutron excess on the fusion cross sections using different proximity-type potentials
Using different types of proximity potentials, we have examined the trend of
variations of barrier characteristics (barrier height and its position) as well
as fusion cross sections for 50 isotopic systems including various collisions
of C, O, Mg, Si, S, Ca, Ar, Ti and Ni nuclei with condition
for compound systems. The results of our studies reveal that the relationships
between increase of barrier positions and decrease of barrier heights are both
linear with increase of ratio. Moreover, fusion cross sections also
enhance linearly with increase of this ratio.Comment: 28 pages, 7 figures, 5 Table
Fragmentation in Peripheral Heavy-Ion Collisions: from Neck Emission to Spectator Decays
Invariant cross sections of intermediate mass fragments in peripheral
collisions of Au on Au at incident energies between 40 and 150 AMeV have been
measured with the 4-pi multi-detector INDRA. The maximum of the fragment
production is located near mid-rapidity at the lower energies and moves
gradually towards the projectile and target rapidities as the energy is
increased. Schematic calculations within an extended Goldhaber model suggest
that the observed cross-section distributions and their evolution with energy
are predominantly the result of the clustering requirement for the emerging
fragments and of their Coulomb repulsion from the projectile and target
residues. The quantitative comparison with transverse energy spectra and
fragment charge distributions emphasizes the role of hard scattered nucleons in
the fragmentation process.Comment: 5 pages, 5 eps figures, RevTeX4, submitted to Phys. Lett.
Perioperative morbidity of radical trachelectomy with lymphadenectomy in early-stage cervical cancer: a French prospective multicentric cohort.
The aim of this study was to determine the predictive factors of postoperative morbidity of patients who have undergone a radical trachelectomy (RT) for early-stage cervical cancer and to assess the oncologic outcomes.
We retrospectively analysed the data of 2 prospective trials on sentinel node biopsy for cervical cancer (SENTICOL I and II). Patients having a RT for early-stage cervical cancer with negative sentinel lymph node and safe margins, were included.
Forty-nine patients met the inclusion criteria. Forty-five patients had a laparoscopic-assisted vaginal technique and 4 patients a total laparoscopic technique. The median age was 32 years (range, 22-46 years). 83.7% of patients had a stage IB1 disease. There were 63.3% squamous cell carcinomas and 34.7% adenocarcinomas. The median follow-up was 46 months (range, 1-85 months). Two patients (3.3%) had a severe postoperative complication (Clavien-Dindo ≥III and/or CTCAE ≥3). The main postoperative complications were urinary (28.6%), lymphovascular (26.5%) and neurologic (14.3%). On a multivariate analysis, postoperative complications were significantly associated with history of pelvic surgery and IB1 International Federation of Gynecology and Obstetrics stage. Inclusion in high surgical skills centers decrease the risk of postoperative complications. During the follow-up, 3 patients (6.1%) had a local recurrence and one patient died from a breast cancer. Between group with complications and group without any complications, overall survival and recurrence-free survival did not significantly differ at 5-year of follow-up.
RT has few severe postoperative complications and appears as a safe alternative to spare fertility of young patients. To guarantee best surgical outcomes, patients should be referred to expert center
Behavioral Response Study on Seismic Airgun and Vessel Exposures in Narwhals
One of the last pristine marine soundscapes, the Arctic, is exposed to increasing anthropogenic activities due to climate-induced decrease in sea ice coverage. In this study, we combined movement and behavioral data from animal-borne tags in a controlled sound exposure study to describe the reactions of narwhals, Monodon monoceros, to airgun pulses and ship noise. Sixteen narwhals were live captured and instrumented with satellite tags and Acousonde acoustic-behavioral recorders, and 11 of them were exposed to airgun pulses and vessel sounds. The sound exposure levels (SELs) of pulses from a small airgun (3.4 L) used in 2017 and a larger one (17.0 L) used in 2018 were measured using drifting recorders. The experiment was divided into trials with airgun and ship-noise exposure, intertrials with only ship-noise, and pre- and postexposure periods. Both trials and intertrials lasted ∼4 h on average per individual. Depending on the location of the whales, the number of separate exposures ranged between one and eight trials or intertrials. Received pulse SELs dropped below 130 dB re 1 μPa2 s by 2.5 km for the small airgun and 4–9 km for the larger airgun, and background noise levels were reached at distances of ∼3 and 8–10.5 km, respectively, for the small and big airguns. Avoidance reactions of the whales could be detected at distances >5 km in 2017 and >11 km in 2018 when in line of sight of the seismic vessel. Meanwhile, a ∼30% increase in horizontal travel speed could be detected up to 2 h before the seismic vessel was in line of sight. Applying line of sight as the criterion for exposure thus excludes some potential pre-response effects, and our estimates of effects must therefore be considered conservative. The whales reacted by changing their swimming speed and direction at distances between 5 and 24 km depending on topographical surroundings where the exposure occurred. The propensity of the whales to move towards the shore increased with increasing exposure (i.e., shorter distance to vessels) and was highest with the large airgun used in 2018, where the whales moved towards the shore at distances of 10–15 km. No long-term effects of the response study could be detected
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