7,851 research outputs found
Isospin-breaking interactions studied through mirror energy differences
Background: Information on charge-dependent (i.e., isospin-non-conserving) interactions is extracted from excited states of mirror nuclei.
Purpose: Specifically, the purpose of the study is to extract effective isovector (Vpp 12Vnn) interactions which, in general, can either be of Coulomb or nuclear origin.
Methods: A comprehensive shell-model description of isospin-breaking effects is used to fit data on mirror energy differences in the A = 42\u201354 region. The angular-momentum dependence of isospin-breaking interactions was determined from a systematic study of mirror energy differences.
Results: The results reveal a significant isovector term, with a very strong spin dependence, beyond that expected of a two-body Coulomb interaction.
Conclusions: The isospin-breaking terms that are extracted have a J dependence that is not consistent with the known CSB properties of the bare nucleon-nucleon interaction
Observer techniques for estimating the state-of-charge and state-of-health of VRLABs for hybrid electric vehicles
The paper describes the application of observer-based state-estimation techniques for the real-time prediction of state-of-charge (SoC) and state-of-health (SoH) of lead-acid cells. Specifically, an approach based on the well-known Kalman filter, is employed, to estimate SoC, and the subsequent use of the EKF to accommodate model non-linearities to predict battery SoH. The underlying dynamic behaviour of each cell is based on a generic Randles' equivalent circuit comprising of two-capacitors (bulk and surface) and three resistors, (terminal, transfer and self-discharging). The presented techniques are shown to correct for offset, drift and long-term state divergence-an unfortunate feature of employing stand-alone models and more traditional coulomb-counting techniques. Measurements using real-time road data are used to compare the performance of conventional integration-based methods for estimating SoC, with those predicted from the presented state estimation schemes. Results show that the proposed methodologies are superior with SoC being estimated to be within 1% of measured. Moreover, by accounting for the nonlinearities present within the dynamic cell model, the application of an EKF is shown to provide verifiable indications of SoH of the cell pack
State-of-charge and state-of-health prediction of lead-acid batteries for hybrid electric vehicles using non-linear observers
The paper describes the application of state-estimation techniques for the real-time prediction of state-of-charge (SoC) and state-of-health (SoH) of lead-acid cells. Approaches based on the extended Kalman filter (EKF) are presented to provide correction for offset, drift and state divergence - an unfortunate feature of more traditional coulomb-counting techniques. Experimental results are employed to demonstrate the relative attributes of the proposed methodolog
Sensitivity of the r-process to nuclear masses
The rapid neutron capture process (r-process) is thought to be responsible
for the creation of more than half of all elements beyond iron. The scientific
challenges to understanding the origin of the heavy elements beyond iron lie in
both the uncertainties associated with astrophysical conditions that are needed
to allow an r-process to occur and a vast lack of knowledge about the
properties of nuclei far from stability. There is great global competition to
access and measure the most exotic nuclei that existing facilities can reach,
while simultaneously building new, more powerful accelerators to make even more
exotic nuclei. This work is an attempt to determine the most crucial nuclear
masses to measure using an r-process simulation code and several mass models
(FRDM, Duflo-Zuker, and HFB-21). The most important nuclear masses to measure
are determined by the changes in the resulting r-process abundances. Nuclei
around the closed shells near N=50, 82, and 126 have the largest impact on
r-process abundances irrespective of the mass models used.Comment: 5 pages, 4 figures, accepted in European Physical Journal
Empirical Evaluation of the Parallel Distribution Sweeping Framework on Multicore Architectures
In this paper, we perform an empirical evaluation of the Parallel External
Memory (PEM) model in the context of geometric problems. In particular, we
implement the parallel distribution sweeping framework of Ajwani, Sitchinava
and Zeh to solve batched 1-dimensional stabbing max problem. While modern
processors consist of sophisticated memory systems (multiple levels of caches,
set associativity, TLB, prefetching), we empirically show that algorithms
designed in simple models, that focus on minimizing the I/O transfers between
shared memory and single level cache, can lead to efficient software on current
multicore architectures. Our implementation exhibits significantly fewer
accesses to slow DRAM and, therefore, outperforms traditional approaches based
on plane sweep and two-way divide and conquer.Comment: Longer version of ESA'13 pape
Electromagnetic Dipole Strength in Transitional Nuclei
Electromagnetic dipole absorption cross-sections of transitional nuclei with
large-amplitude shape fluctuations are calculated in a microscopic way by
introducing the concept of Instantaneous Shape Sampling. The concept bases on
the slow shape dynamics as compared to the fast dipole vibrations. The
elctromagnetic dipole strength is calculated by means of RPA for the
instantaneous shapes, the probability of which is obtained by means of IBA.
Very good agreement with the experimental absorption cross sections near the
nucleon emission threshold is obtained.Comment: 4 pages, 4 figure
The footprint of cometary dust analogs: I. Laboratory experiments of low-velocity impacts and comparison with Rosetta data
Cometary dust provides a unique window on dust growth mechanisms during the
onset of planet formation. Measurements by the Rosetta spacecraft show that the
dust in the coma of comet 67P/Churyumov-Gerasimenko has a granular structure at
size scales from sub-um up to several hundreds of um, indicating hierarchical
growth took place across these size scales. However, these dust particles may
have been modified during their collection by the spacecraft instruments. Here
we present the results of laboratory experiments that simulate the impact of
dust on the collection surfaces of COSIMA and MIDAS, instruments onboard the
Rosetta spacecraft. We map the size and structure of the footprints left by the
dust particles as a function of their initial size (up to several hundred um)
and velocity (up to 6 m/s). We find that in most collisions, only part of the
dust particle is left on the target; velocity is the main driver of the
appearance of these deposits. A boundary between sticking/bouncing and
fragmentation as an outcome of the particle-target collision is found at v ~ 2
m/s. For velocities below this value, particles either stick and leave a single
deposit on the target plate, or bounce, leaving a shallow footprint of
monomers. At velocities > 2 m/s and sizes > 80 um, particles fragment upon
collision, transferring up to 50 per cent of their mass in a rubble-pile-like
deposit on the target plate. The amount of mass transferred increases with the
impact velocity. The morphologies of the deposits are qualitatively similar to
those found by the COSIMA instrument.Comment: 14 pages, 12 figures, accepted for publication in MNRA
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