177,271 research outputs found
Heavy-Ion Fusion Targets with 'Diffuse' Spherical Radiation Converter
No full textSpherically symmetric targets for indirect-drive heavy-ion fusion are studied, in which the fusion capsule is enclosed in a low-density thick spherical shell, where the ion beams are stopped and their energy is converted into thermal radiation. The thermal radiation then drives the implosion of the fusion capsule, with mininum hydrodynamic coupling between the energy deposition region and the ablation layer. The conditions for effective hydrodynamic decoupling have been derived. It is found that with the use of heavy ions with energy about or below 8 GeV, the beam-to-fuel energy coupling efficiency can be as large as in foreseen conventional hohlraums. On the other hand, these targets only allow for a low dynamic range of pulse shaping, which results in rather poor entropy shaping and modest fuel gain. Robust targets have been designed, which achieve energy gain G approximate to 30, when driven by shaped pulses of 12.5 MJ of 8.5 GeV Bi ions. Inclusion of a high-density pusher, which increases the fuel compression leads to higher gain at lower beam energy, but two-dimensional simulations demonstrate the extremely violent instability of the fuel-pusher interface
Spherically Symmetric Radiation Converters for Ion Beam Fusion
No full textThick spherical shells, irradiated nearly symmetrically by ion beams, can convert efficiently ion beam energy to thermal radiation, with parameters of relevance to inertial confinement fusion. The evolution of such radiation converters has been studied by means of an analytic model, in turn validated by 1D radiation hydrodynamic simulations. Expressions are derived for the overall conversion efficiency, the heating time and the radiation temperature as a function of the beam and target parameters. Conditions are also derived for the effective hydrodynamic insulation between the converter and the fusion capsule contained inside the converter. For realistic heavy ion beam parameters (e.g. 6-8 GeV Bi beams, with total energy of 10 MJ and power about 700 TW) such converters can achieve an efficiency adequate for fusion applications, but only allow for a modest dynamic range of pulse shaping
Implosion of Reactor Size, Gas Filled, Spherical Shell Targets Driven by Shaped Pressure Pulses
No full textThe implosion of a family of reactor‐size targets for inertial confinement fusion (ICF) is studied analytically and numerically. The targets consist of a deuterium–tritium (D–T) shell filled with D–T vapor and they are imploded by a multistep pressure pulse designed in such a way that the final hot spot is formed mainly from the initially gaseous fuel. The formation of the hot spot is described by means of a relatively simple model, and scaling laws for the quantities that characterize the state of the initially gaseous part of the fuel prior to ignition are derived. The results of the model are compared with one‐dimensional fluid simulations, and good agreement is found. A parametric study of the fuel energy gain is then presented; the dependence of the gain and of the hot spot convergence ratio on the pulse parameters and on the filling gas density is analyzed. It is also shown that a substantial increase in the gain (for a given target and pulse energy) can be achieved by replacing the last step of the pulse with an exponential ramp
Evaluation of the Time and Frequency Transfer Capabilities of a network of GNSS receivers located in timing laboratories
No full textNear-real time synchronization through a network of GNSS receivers located in timinglaboratories
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Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
ERS-1 Orbits: The Routine Operation and High Precision Products
No full textThe objective of the paper is to summarise the experience of one year of orbit determination and prediction for the ERS-1 spacecraft: firstly, the results of the operational solutions based on S-band ranging and doppler plus fast delivery altimetry will be discussed, and subsequently, higher precision solutions using data from the global laser ranging network. Steady progress has been achieved in improving the latter, in particular through better solutions for station positions, drag, gravity and tides. The development of this offline capability has strengthened considerably the routine orbit determination, and gives high confidence that the requirements for the latter are being satisfied. The paper attempts to quantify the accuracies which have been reached in the European Space Operations Center solutions, and to answer the question: how far are we still from achieving 10 cm radial accuracy for altimeter satellites at 800 km
Ignition Conditions and Fuel Energy Gain of Spark-Ignited and Volume-Ignited ICF Targets
No full textMetaphorical Reasoning in Comprehension And Translation: An Analysis Of Metaphor In Multiple Translations
No full textMetaphor is largely seen as a problem for translation (Philip 2016), but very little empirical research has been conducted to illustrate precisely how it is problematic and – crucially – how translators deal with it in practice. This study seeks to fill the gap: it uses corpus linguistics methods to compare multiple translations prepared by Modern Languages students (EQF level 5, English proficiency C1-C2) over the course of their year-long module on English-to-Italian translation. The translations of each source text are submitted weekly by email and converted into a small corpus to facilitate viewing of examples for comment and analysis in class. By projecting KWIC concordances of the translations for each language item of interest, it is possible to compare similarities and differences between the students’ translations, and to comment on the translation strategies adopted (consciously or otherwise). These include: a tendency for weaker students to translate metaphorical meanings as literal and to translate unfamiliar literal meanings as metaphorical; an overall tendency for metaphors to be flattened out (Baker 1993) and/or simplified (ibid.) in translation, with general terms being used in favour of specific ones, and evaluative/ pragmatic aspects of meaning very often overlooked entirely; explicitation (ibid) of culturally-specific metaphors; and considerable difficulty in detaching meaning from form, particularly by maintaining the source language’s metaphor source domain when a different source domain would be more apt in the target language. The presentation will discuss the relationship between general translation strategies and the translation of metaphor, including examples of the problems identified
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