197,354 research outputs found
Polarized Fusion: An Idea More Than Thirty Years Old! What Are We Waiting For?
No full textThe present status of the fusion research is strictly connected to government
investments on the corresponding research projects like ITER, or the proposed
IGNITOR and DEMO reactors. The production of energy by nuclear fusion is a perfect
option that could give “breath” to the planet. Recent agreements on limiting the
global climate change and plans for our future life on the planet require the reduction
of energy production by carbon-based resources. But even the use of nuclear
resources by fission implicates a non negligible risk for our civilization, either by
disasters like in Chernobyl or in Fukushima, or by the release of the fission products
into environment. CO2 emissions into the atmosphere and the growing and developing
population urgently require to put more effort into fusion programs worldwide.
An additional option for any fusion program could be the use of polarized fuel. It
still requires intense effort on the development of the necessary technologies, but it
is a realistic option to increase the energy output of different types of fusion reactors
and to increase the cost efficiency. First of all we would like to give an overview on
the current situation in energy production and recent climate development. Secondly,
we would like to provide an introduction to the contents of this volume, devoted to
nuclear fusion using polarized fuels
Nuclear Fusion with Polarized Fuel
No full textThis book offers a detailed examination of the latest work on the potential of polarized fuel to realize the vision of energy production by nuclear fusion. It brings together contributions from nuclear physicists and fusion physicists with the aims of fostering exchange of information between the two communities, describing the current status in the field, and examining new ideas and projects under development.
It is evident that polarized fuel can offer huge improvements for the first generation of fusion reactors and open new technological possibilities for future generations, including neutron lean reactors, which could be the most popular and sustainable energy production option to avoid environmental problems. Nevertheless, many questions must be resolved before polarized fuel can be used for energy production in the different reactor types. Readers will find this book to be a stimulating source of information on the key issues. It is based on contributions from leading scientists delivered at the meetings “Nuclear Fusion with Polarized Nucleons” (Trento, November 2013) and “PolFusion” (Ferrara, July 2015)
Polarized Fusion. Can Polarization Help to Increase the Energy Output of Fusion Reactors?
No full textSince more than 60 years scientists are working on the idea to produce energy from
nuclear fusion of light particles like the Hydrogen isotopes. In the meantime, the
energy output of e.g. tokamak reactors was increased by five orders and modern
experiments like JET are approaching the border for energy production. The international
ITER collaboration is preparing the first fusion reactor that will produce
about ten times more energy, compared to the energy that is needed to run the
experiment. Today, the laser-induced inertial fusion reached the same level and
experiments at the National Ignition Facility (NIF) in California, USA, demonstrate
a ratio between produced and induced energy about one at the end of 2013.1
In parallel, it is discussed since 1970 to use nuclear polarized fuel to increase the
total cross sections of the different fusion reactions.2 The energy gain of fusion reactors
does not depend linearly on the total cross section. Depending on the different
concepts for nuclear fusion, magnetic confinement or inertial fusion, the energy gain
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R. Engels & G. Ciullo
is improved above average. M. Temporal et al. have shown, e.g., that the energy
gain of laser-induced inertial fusion might be increased by a factor four, or that
the necessary laser power can be reduced by 20 %, if the nuclear fuel was polarized
before.3 The downsized laser power will reduce the costs of the corresponding
project by a reasonable amount. In addition, the differential cross sections can be
modified so that it will be possible to focus the ejectiles, e.g. the neutrons, on special
wall areas. In a tokamak this can be used to concentrate the neutron flux to special
outer parts of the blanket, where the cooling can be improved and the neutrons be
used for Tritium production via the exothermic reaction 6Li+n → 4He+t.4 At the
same time, less cooling is needed for the inner parts of the blanket that allows to
bring the magnetic field coils closer to the fusion plasma. The increased magnetic
field in the plasma will increase the energy gain additionally. Another option of
polarized fuel is a new kind of plasma diagnostic inside a tokamak. In combination
with modern Nuclear Magnetic Resonance technologies (NMR) anisotropies in the
plasma can be measured to learn more about the different plasma mode
How much can large-scale Video-On-Demand benefit from users' cooperation?
No full textWe propose an analytical framework to tightly characterize the scaling laws for the additional bandwidth that servers must supply to guarantee perfect service in peer-assisted Video-on-Demand systems, taking into account essential aspects such as peer churn, bandwidth heterogeneity, and Zipf-like video popularity. Our results reveal that the catalog size and the content popularity distribution have a huge effect on the system performance. We show that users' cooperation can effectively reduce the servers' burden for a wide range of system parameters, confirming to be an attractive solution to limit the costs incurred by content providers as the system scales to large populations of user
The PolFusion Experiment: Measurement of the d-d-Fusion Spin-Dependence
No full textA double-polarized dd-fusion experiment is under preparation at PNPI,
Gatchina. The experimental program includes themeasurements of the asymmetry in
the differential cross section of the reactions d_pol + d_pol → 3He + n and d_pol + d_pol → t + p. The spin-correlation coefficients Cz,z and Czz,zz will be measured to determine
the quintet-state suppression factors for both reactions, for which quite different
theoretical predictions were made and which are very important for the design of
future neutron-lean fusion reactors. The total cross sectionmodification for polarized
d–d fusion will also be investigated. An increase by a factor of 1.5 was already
deduced for the d + 3He and the d + t reactions. The experimental setup and the
future upgrade plans are described
Energy-Aware Base Stations: The Effect of Planning, Management, and Femto Layers
No full textWe compare the performance of three base station management schemes on three different network topologies. In addition, we explore the effect of offloading traffic to heterogeneous femtocell layer upon energy savings taking into account the increase of base station switch-off time intervals. Fairness between mobile operator and femtocell owners is maintained since current femtocell technologies present flat power consumption curves with respect to served traffic. We model two different user-to-femtocell association rules in order to capture realistic and maximum gains from the heterogeneous network. To provide accurate findings and a holistic overview of the techniques, we explore a real urban district where channel estimations and power control are modeled using deterministic algorithms. Finally, we explore energy efficiency metrics that capture savings in the mobile network operator, the required watts per user and watts per bitrate. It is found that the newly established pseudo distributed management scheme is the most preferable solution for practical implementations and together with the femotcell layer the network can handle dynamic load control that is regarded as the basic element of future demand response programs
Recurrent lacunar strokes in a patient with small vessel disease: rare but not negligible cause of Foix-Chavany-Marie syndrome
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