441 research outputs found
Constrained Molecular Dynamics II: a N-body approach to nuclear systems
In this work we illustrate the basic development of the constrained molecular
dynamics applied to the N-body problem in nuclear physics. The heavy
computational taskes related to quantum effects, to the presence of the "hard
core" repulsive interaction have been worked out by defining a set of
transformations based on the concept of impulsive forces. In particular in the
implemented version II of the Constrained Molecular Dynamics model the problem
related to the non conservation of the total angular momentum has been solved.
This problem can affect others semiclassical microscopic approaches as due to
the "hard core" repulsive interaction or to the use of stochastic forces. The
effect of the restored conservation law on the fusion cross section for
40Ca+40Ca system is also briefly discussed.Comment: Tex version 3.1459 (Web2C 7.3.1);main text+fig.cap in .tex 13 page;
+4 figures .ps;the order and the numerical label of the figure files reflect
the figure numbers in the main tex and captions, Submited to Journal of
computational physic
Seismic and aseismic deformation along the East African Rift System from a reanalysis of the GPS velocity field of Africa
International audienceThe improvement of the geodetic coverage within the African Plate over the last decade together with an extended GPS position time-series allows improved accuracy in determining the velocity field than prior geodetic studies. Using this new velocity field of the whole African continent, the best model proposed here remains consistent with previous studies including the existence of two small plates along the East African Rift System (EARS, Victoria and Rovuma).We focus specifically on the velocities along this plate boundary by estimating both the geodetic and the seismic moment rate.Whereas we use a scalar form of the Kostrov relation to calculate the geodetic moment rate, the seismic moment rate is obtained by integrating the cumulative truncated Gutenberg-Richter earthquake distribution of local events in the 39-yr-long worldwide catalogue, using a maximum likelihood method. This statistical method allows us to take into account the probable incompleteness of the existing catalogue and to assume the seismic moment rate calculated from this short catalogue to be representative of the long-term seismic deformation. The comparison of geodetic and seismic energy release sheds light on the variations of mechanical behaviour related to intracontinental extension along the EARS. The southward increase, observed along the rift, of the proportion of geodetic moment seismically accommodated suggests a significant control of the thermal structure associated with different states of rifting evolution
How does the elastic scattering of 12C + 20Ne compare with that of 16O + 16O ?
Excitation functions for 5 exit channels of the 12C + 20Ne system are given in the range 22-28 MeV centre of mass incident energy. An important structure is observed in the elastic scattering excitation functions taken at 90° and 130° (C.M.). This structure, which reminds one of the 16O + 16O case, is studied in terms of angular momentum matching. An angular distribution taken at 24.7 MeV (C.M.) is also presented. The direct channel absorption is shown to be intermediate between the 16O + 16O and 18O + 18O cases
DISTRIBUTIONS ISOTOPIQUES DES PRODUITS DE TRANSFERTS TRĂS INĂLASTIQUES ENTRE IONS LOURDS
On compare les distributions isotopiques expérimentales des produits de transfert trÚs inélastiques obtenus par les réactions 40Ca (284 MeV) + 40Ca et 40Ar (295 MeV) + 232Th
Lower Crustal Earthquakes in the March 2018 Sequence Along the Western Margin of Afar
During the evolution of continental rift systems, extension is thought to progressively focus in-rift to the future breakup boundary while faults along the rift margins progressively deactivate. However, observational constraints on how strain is partitioned between rift axis and rift margins are still lacking. The Afar rift records the latest stages of rifting and incipient continental breakup. Here, we analyzed the recent MW 5.2 earthquake on the Western Afar Margin on March 24, 2018 and the associated seismic sequence of >500 earthquakes using 24 temporary seismic stations deployed during 2017â2018. We show seismicity occurring at lower crustal depths, from âŒ15 to âŒ30 km, with focal mechanisms and relocated earthquakes highlighting both west-dipping and east-dipping normal faults. We tested earthquake depth using InSAR by processing six independent interferograms using Sentinel-1 data acquired from both ascending and descending tracks. None of them shows evidence of surface deformation. We tested possible ranges of depth by producing forward models for a fault located at progressively increasing depths. Models show that surface deformation is not significant for fault slip at depths greater than 15 km, in agreement with the hypocentral depth of 19 km derived from seismic data for the largest earthquake. Due to the localized nature of deep earthquakes near hot springs coupled with subsurface evidence for magmatism, we favor an interpretation of seismicity induced by migrating fluids such as magma or CO2. We suggest that deep fluid migration can occur at the rifted-margin influencing seismicity during incipient continental rupture
Lower Crustal Earthquakes in the March 2018 Sequence Along the Western Margin of Afar
During the evolution of continental rift systems, extension is thought to progressively focus in-rift to the future breakup boundary while faults along the rift margins progressively deactivate. However, observational constraints on how strain is partitioned between rift axis and rift margins are still lacking. The Afar rift records the latest stages of rifting and incipient continental breakup. Here, we analyzed the recent M
W 5.2 earthquake on the Western Afar Margin on March 24, 2018 and the associated seismic sequence of >500 earthquakes using 24 temporary seismic stations deployed during 2017â2018. We show seismicity occurring at lower crustal depths, from âŒ15 to âŒ30 km, with focal mechanisms and relocated earthquakes highlighting both west-dipping and east-dipping normal faults. We tested earthquake depth using InSAR by processing six independent interferograms using Sentinel-1 data acquired from both ascending and descending tracks. None of them shows evidence of surface deformation. We tested possible ranges of depth by producing forward models for a fault located at progressively increasing depths. Models show that surface deformation is not significant for fault slip at depths greater than 15 km, in agreement with the hypocentral depth of 19 km derived from seismic data for the largest earthquake. Due to the localized nature of deep earthquakes near hot springs coupled with subsurface evidence for magmatism, we favor an interpretation of seismicity induced by migrating fluids such as magma or CO
2. We suggest that deep fluid migration can occur at the rifted-margin influencing seismicity during incipient continental rupture.
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Plate-Boundary Kinematics of the Afrera Linkage Zone (Afar) From InSAR and Seismicity
International audienceStudying the mechanisms of interaction between rift segments is key to understanding the kinematics of plate boundaries in continental rifts. However, the spatial and temporal evolution of deformation at rift linkage zones is rarely observed directly. Here, we combine InSAR data spanning 2005â2010 and 2014â2019 from ENVISAT and Sentinel-1 satellites, respectively, with local seismicity from the Afar rift to investigate the plate-boundary kinematics of the Afrera linkage zone, the junction between the Erta Ale and Tat Ali magmatic segments in Northern Afar (Ethiopia). We obtain time-series of cumulative InSAR Line-Of-Sight (LOS) displacements that show deformation is accommodated by a series of active en-echelon faults striking âŒNS and characterized by normal slip associated with a left-lateral strike-slip component. Additionally, we observe spatial variation in fault behavior with stick-slip and creep. The faults in the center of the linkage zone behave primarily in a stick-slip mode (with abrupt fault displacements up to âŒ40 mm) and fault motions are associated with earthquakes of ML > 5. Conversely, faults at the edge of the linkage zone, near the magmatic segments, show creep and some stick-slip behavior (with cumulative LOS displacement up to âŒ30â40 mm over a âŒ5-year period) accompanied by low-level seismicity. Some of the creeping faults are also spatially associated with hydrothermal springs. We interpret that the temporal behavior of the faults in the linkage zone is controlled by the interplay between tectonic extension, high heat flows, and fluid circulation near the magmatic segments where creeping of some faults is favored
Precision mass measurements of very short-lived, neutron-rich Na isotopes using a radiofrequency spectrometer
Mass measurements of high precision have been performed on sodium isotopes out to Na using a new technique of radiofrequency excitation of ion trajectories in a homogeneous magnetic field. This method, especially suited to very short-lived nuclides, has allowed us to significantly reduce the uncertainty in mass of the most exotic Na isotopes: a relative error of 5x10 was achieved for Na having a half-life of only 30.5 ms and 9x10 for the weakly produced Na. Verifying and minimizing binding energy uncertainties in this region of the nuclear chart is important for clarification of a long standing problem concerning the strength of the =20 magic shell closure. These results are the fruit of the commissioning of the new experimental program Mistral
The unexpected Mayotte 2018â2020 seismic sequence: a reappraisal of the regional seismicity of the Comoros
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