669 research outputs found
Geodesic motions versus hydrodynamic flows in a gravitating perfect fluid: Dynamical equivalence and consequences
Stimulated by the methods applied for the observational determination of
masses in the central regions of the AGNs, we examine the conditions under
which, in the interior of a gravitating perfect fluid source, the geodesic
motions and the general relativistic hydrodynamic flows are dynamically
equivalent to each other. Dynamical equivalence rests on the functional
similarity between the corresponding (covariantly expressed) differential
equations of motion and is obtained by conformal transformations. In this case,
the spaces of the solutions of these two kinds of motion are isomorphic. In
other words, given a solution to the problem "hydrodynamic flow in a perfect
fluid", one can always construct a solution formally equivalent to the problem
"geodesic motion of a fluid element" and vice versa. Accordingly, we show that,
the observationally determined nuclear mass of the AGNs is being overestimated
with respect to the real, physical one. We evaluate the corresponding
mass-excess and show that it is not always negligible with respect to the mass
ofthe central dark object, while, under circumstances, can be even larger than
the rest-mass of the circumnuclear gas involved.Comment: LaTeX file, 22 page
Novel Techniques for Constraining Neutron-Capture Rates Relevant for r-Process Heavy-Element Nucleosynthesis
The rapid-neutron capture process ( process) is identified as the producer
of about 50\% of elements heavier than iron. This process requires an
astrophysical environment with an extremely high neutron flux over a short
amount of time ( seconds), creating very neutron-rich nuclei that are
subsequently transformed to stable nuclei via decay. One key
ingredient to large-scale -process reaction networks is radiative
neutron-capture () rates, for which there exist virtually no data for
extremely neutron-rich nuclei involved in the process. Due to the current
status of nuclear-reaction theory and our poor understanding of basic nuclear
properties such as level densities and average -decay strengths,
theoretically estimated () rates may vary by orders of magnitude and
represent a major source of uncertainty in any nuclear-reaction network
calculation of -process abundances. In this review, we discuss new
approaches to provide information on neutron-capture cross sections and
reaction rates relevant to the process. In particular, we focus on
indirect, experimental techniques to measure radiative neutron-capture rates.
While direct measurements are not available at present, but could possibly be
realized in the future, the indirect approaches present a first step towards
constraining neutron-capture rates of importance to the process.Comment: 62 pages, 24 figures, accepted for publication in Progress in
Particle and Nuclear Physic
A Simple Synchro – Modal Decision Support Tool for the Piraeus Container Terminal
AbstractThe concept of Synchro modality is effectively an evolution of a multimodal supply chain. It integrates different transport modes and gives shippers and logistics service providers the freedom to deploy different modes of transportation in the same chain and in a flexible way so as to gain the desired outcome according to their priorities in a certain trip. Time, costs and emissions are certainly the three most relevant parameters when talking about a multimodal transportation chain. In most cases the logistics provider has set priorities to conform with, and obviously above mentioned constrains influence each other in an adverse way. With the development of ICT technologies and systems installed on board and on shore and with a simple decision support system fed with input from tracking and tracing systems or traffic monitoring systems, one can easily and flexibly plan his transportation job and maintain his set priority while in parallel keeping the remaining two parameters in control. Down times for example could be eliminated and efficiency gains could be achieved with decreased environmental footprint.The Port of Piraeus is the largest Greek seaport and one of the largest ports in the Mediterranean Sea basin. It exhibits an impressive container traffic growth rate over the last 4 years triggered by its partial privatization and a recently completed hinterland connection to the rail network, which associated the port with the South-Eastern European corridor e.g. the route Far Eastern ports–Piraeus–Prague.The current paper will present an easy to use simple tool to continuously assess even during the transportation event all the alternative modes for a given destination in terms of time cost and emissions. An analytical fully parameterized model will be the basis for this tool which will be run for the chain Shanghai–Piraeus–Prague. The overall scenario is as follows: A container ship is arriving from China to the Piraeus Container Terminal. One of its containers is destined to an inland Enterprise in Prague. The most common way for transportation to Prague is rail, but also truck could be an alternative solution and of course a combination of a Short Sea Shipping part to Thessaloniki and then truck or train to Prague. Emphasis in the calculations will be given to emissions for all the modes and relations will be shown with time and cost.The tool developed is based on the case study above, being however open architecture software it can be expanded and applied to other ports and routes. The final outcome will be an easy and user friendly tool with the possibility to alter different input parameters and receive quickly a useful decision support system for the shipper or the logistics providers. Finally, there are two loops foreseen for the runs of the program. The required input parameters at each stage are either directly fed to the program if available (e.g vessels ETA and position through GPS, VTS, ETC) or calculated if this is not the case
Exploiting neutron-rich radioactive ion beams to constrain the symmetry energy
The Modular Neutron Array (MoNA) and 4 Tm Sweeper magnet were used to measure
the free neutrons and heavy charged particles from the radioactive ion beam
induced 32Mg + 9Be reaction. The fragmentation reaction was simulated with the
Constrained Molecular Dynamics model(CoMD), which demonstrated that the
of the heavy fragments and free neutron multiplicities were observables
sensitive to the density dependence of the symmetry energy at sub-saturation
densities. Through comparison of these simulations with the experimental data
constraints on the density dependence of the symmetry energy were extracted.
The advantage of radioactive ion beams as a probe of the symmetry energy is
demonstrated through examination of CoMD calculations for stable and
radioactive beam induced reactions
Integrating children's perspectives in policy-making to combat poverty and social exclusion experienced by single-parent families: a transnational comparative approach
This is the final report of a research project that addressed social exclusion and poverty as it relates to single parent families and their children in particular. The rising numbers of single parent families and
children throughout the EU and the increased likelihood that these families will live in poverty and experience many different forms of social exclusion in their daily lives brings in sharp focus the need to address the issue as an urgent one in our efforts to eradicate poverty and social exclusion. The focus on the children of single parent
families seeks to rectify a long-standing problem in our knowledge and understanding of single parent families and the social problems they face, namely, the fact that little, if anything, is known about how these children experience and understand their lives as members of these families. The research set out to contribute to policy development and the transnational exchange of best practice by adding a much-neglected dimension on single parent families. The project used a cross-national comparative qualitative research design and methods (Mangen 1999) which involved all partners in the design of each research phase
including the analysis; partners were England, Cyprus and Greece
Search for unbound 15Be states in the 3n+12Be channel
15Be is expected to have low-lying 3/2+ and 5/2+ states. A first search did
not observe the 3/2+ [A. Spyrou et al., Phys. Rev. C 84, 044309 (2011)],
however, a resonance in 15Be was populated in a second attempt and determined
to be unbound with respect to 14Be by 1.8(1) MeV with a tentative spin-parity
assignment of 5/2+ [J. Snyder et al., Phys. Rev. C 88, 031303(R) (2013)].
Search for the predicted 15Be 3/2+ state in the three-neutron decay channel. A
two-proton removal reaction from a 55 MeV/u 17C beam was used to populate
neutron-unbound states in 15Be. The two-, three-, and four-body decay energies
of the 12Be + neutron(s) detected in coincidence were reconstructed using
invariant mass spectroscopy. Monte Carlo simulations were performed to extract
the resonance and decay properties from the observed spectra. The low-energy
regions of the decay energy spectra can be described with the first excited
unbound state of 14Be (E_x=1.54 MeV, E_r=0.28 MeV). Including a state in 15Be
that decays through the first excited 14Be state slightly improves the fit at
higher energies though the cross section is small. A 15Be component is not
needed to describe the data. If the 3/2+ state in 15Be is populated, the decay
by three-neutron emission through 14Be is weak, less than or equal to 11% up to
4 MeV. In the best fit, 15Be is unbound with respect to 12Be by 1.4 MeV
(unbound with respect to $14Be by 2.66 MeV) with a strength of 7%.Comment: 6 pages, 5 figures, accepted in Physical Review
Spin-down of Relativistic Stars with Phase Transitions and PSR J0537-6910
Using a highly accurate numerical code, we study the spin down of rotating
relativistic stars, undergoing a quark deconfinement phase transition. Such
phase transitions have been suggested to yield an observable signal in the
braking index of spinning-down pulsars, which is based on a ``backbending''
behaviour of the moment of inertia. We focus on a particular equation of state
that has been used before to study this behaviour, and find that for the
population of normal pulsars the moment of inertia does not exhibit a
backbending behaviour. In contrast, for supramassive millisecond pulsars a very
strong backbending behaviour is found. Essentially, once a quark core appears
in a spinning-down supramassive millisecond pulsar, the star spins up and
continues to do so until it reaches the instability to collapse. This strong
spin-up behaviour makes it easier to distinguish a phase transition in such
pulsars: a negative first time-derivative of the rotational period suffices and
one does not have to measure the braking index. In the spin-up era, the usually
adopted spin-down power law fails to describe the evolution of the angular
velocity. We adopt a general-relativistic spin-down power law and derive the
equations that describe the angular velocity and braking index evolution in
rapidly rotating pulsars.Comment: 10 pages, 10 figures, additional results and conclusions, matches
published versio
Three-body correlations in the ground-state decay of 26O
Background: Theoretical calculations have shown that the energy and angular
correlations in the three-body decay of the two-neutron unbound O26 can provide
information on the ground-state wave function, which has been predicted to have
a dineutron configuration and 2n halo structure.
Purpose: To use the experimentally measured three-body correlations to gain
insight into the properties of O26, including the decay mechanism and
ground-state resonance energy.
Method: O26 was produced in a one-proton knockout reaction from F27 and the
O24+n+n decay products were measured using the MoNA-Sweeper setup. The
three-body correlations from the O26 ground-state resonance decay were
extracted. The experimental results were compared to Monte Carlo simulations in
which the resonance energy and decay mechanism were varied.
Results: The measured three-body correlations were well reproduced by the
Monte Carlo simulations but were not sensitive to the decay mechanism due to
the experimental resolutions. However, the three-body correlations were found
to be sensitive to the resonance energy of O26. A 1{\sigma} upper limit of 53
keV was extracted for the ground-state resonance energy of O26.
Conclusions: Future attempts to measure the three-body correlations from the
ground-state decay of O26 will be very challenging due to the need for a
precise measurement of the O24 momentum at the reaction point in the target
Population of 13Be in a Nucleon Exchange Reaction
The neutron-unbound nucleus 13Be was populated with a nucleon-exchange
reaction from a 71 MeV/u secondary 13B beam. The decay energy spectrum was
reconstructed using invariant mass spectroscopy based on 12Be fragments in
coincidence with neutrons. The data could be described with an s-wave resonance
at E = 0.73(9) MeV with a width of Gamma = 1.98(34) MeV and a d-wave resonance
at E = 2.56(13) MeV with a width of Gamma = 2.29(73) MeV. The observed spectral
shape is consistent with previous one-proton removal reaction measurements from
14B.Comment: Published in Phys. Rev.
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