1,024 research outputs found
Ground state magnetic dipole moment of 35K
The ground state magnetic moment of 35K has been measured using the technique
of nuclear magnetic resonance on beta-emitting nuclei. The short-lived 35K
nuclei were produced following the reaction of a 36Ar primary beam of energy
150 MeV/nucleon incident on a Be target. The spin polarization of the 35K
nuclei produced at 2 degrees relative to the normal primary beam axis was
confirmed. Together with the mirror nucleus 35S, the measurement represents the
heaviest T = 3/2 mirror pair for which the spin expectation value has been
obtained. A linear behavior of gp vs. gn has been demonstrated for the T = 3/2
known mirror moments and the slope and intercept are consistent with the
previous analysis of T = 1/2 mirror pairs.Comment: 14 pages, 5 figure
Elasto-viscoplastic modeling of subsidence above gas fields in the Adriatic Sea
Abstract. From the analysis of GPS monitoring data collected above gas
fields in the Adriatic Sea, in a few cases subsidence responses have been
observed not to directly correlate with the production trend. Such behavior,
already described in the literature, may be due to several physical
phenomena, ranging from simple delayed aquifer depletion to a much more
complex time-dependent mechanical response of subsurface geomaterials to
fluid withdrawal. In order to accurately reproduce it and therefore to be
able to provide reliable forecasts, in the last years Eni has enriched its
3D finite element geomechanical modeling workflow by adopting an advanced
constitutive model (Vermeer and Neher, 1999), which also considers the
viscous component of the deformation. While the numerical implementation of
such methodology has already been validated at laboratory scale and tested
on synthetic hydrocarbon fields, the work herein presents its first
application to a real gas field in the Adriatic Sea where the phenomenon has
been observed. The results show that the model is capable to reproduce very
accurately both GPS data and other available measurements. It is worth
remarking that initial runs, characterized by the use of model parameter
values directly obtained from the interpretation of mechanical laboratory
tests, already provided very good results and only minor tuning operations
have been required to perfect the model outcomes. Ongoing R&D projects
are focused on a regional scale characterization of the Adriatic Sea basin
in the framework of the Vermeer and Neher model approach
Multifractal properties of return time statistics
Fluctuations in the return time statistics of a dynamical system can be
described by a new spectrum of dimensions. Comparison with the usual
multifractal analysis of measures is presented, and difference between the two
corresponding sets of dimensions is established. Theoretical analysis and
numerical examples of dynamical systems in the class of Iterated Functions are
presented.Comment: 4 pages, 3 figure
Estimate of a spatially variable reservoir compressibility by assimilation of ground surface displacement data
Abstract.
Fluid extraction from producing hydrocarbon reservoirs can cause anthropogenic land subsidence. In
this work, a 3-D finite-element (FE) geomechanical model is used to predict the land surface displacements above
a gas field where displacement observations are available. An ensemble-based data assimilation (DA) algorithm
is implemented that incorporates these observations into the response of the FE geomechanical model, thus re-
ducing the uncertainty on the geomechanical parameters of the sedimentary basin embedding the reservoir. The
calibration focuses on the uniaxial vertical compressibility
c
M
, which is often the geomechanical parameter to
which the model response is most sensitive. The partition of the reservoir into blocks delimited by faults moti-
vates the assumption of a heterogeneous spatial distribution of
c
M
within the reservoir. A preliminary synthetic
test case is here used to evaluate the effectiveness of the DA algorithm in reducing the parameter uncertainty
associated with a heterogeneous
c
M
distribution. A significant improvement in matching the observed data is
obtained with respect to the case in which a homogeneous
c
M
is hypothesized. These preliminary results are
quite encouraging and call for the application of the procedure to real gas fields
Generating a Fractal Butterfly Floquet Spectrum in a Class of Driven SU(2) Systems
A scheme for generating a fractal butterfly Floquet spectrum, first proposed
by Wang and Gong [Phys. Rev. A {\bf 77}, 031405(R) (2008)], is extended to
driven SU(2) systems such as a driven two-mode Bose-Einstein condensate. A new
class of driven systems without a link with the Harper model context is shown
to have an intriguing butterfly Floquet spectrum. The found butterfly spectrum
shows remarkable deviations from the known Hosftadter's butterfly. In addition,
the level crossings between Floquet states of the same parity and between
Floquet states of different parities are studied and highlighted. The results
are relevant to studies of fractal statistics, quantum chaos, coherent
destruction of tunneling, as well as the validity of mean-field descriptions of
Bose-Einstein condensates.Comment: 11 pages, 9 figures, relatively large size, a full-length report of
the findings in arXiv 0906.225
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