337 research outputs found
On Granger-causality and the effect of interventions in time series
No full textWe combine two approaches to causal reasoning. Granger-causality, on the one hand, is popular in fields like econometrics, where randomised experiments are not very common. Instead information about the dynamic development of a system is explicitly modelled and used to define potentially causal relations. On the other hand, the notion of causality as effect of interventions is predominant in fields like medical statistics or computer science. In this paper, we consider the effect of external, possibly multiple and sequential, interventions in a system of multivariate time series, the Granger-causal structure of which is taken to be known. We address the following questions: under what assumptions about the system and the interventions does Granger-causality inform us about the effectiveness of interventions, and when does the possibly smaller system of observable times series allow us to estimate this effect? For the latter we derive criteria that can be checked graphica lly and are in the same spirit as Pearl''s back-door and front-door criteria (Pearl 1995).econometrics;
Towards the polarization of DT molecules
No full textInternational audienceThe polarization of D and T nuclei should increase the reactivity of DT molecules in HIIF processes. At IPN Orsay, we have developed the static polarization of HD samples using “brute force” (BF). It has been demonstrated, that the ageing technique or the double distillation allow to get nuclear relaxation times larger than 1 h, even at 1.5 K and 1 T. It is advocated that it is possible to achieve by RF the conventional Dynamic Nuclear Polarization (DNP) of the proton and the deuteron contained in the HD molecule, using HD samples distilled at Orsay and suitably irradiated. The persistence after irradiation of the long nuclear relaxation times resulting from the double distillation has already been demonstrated. If feasible, the DNP of HD would ope
ETUDE DES REACTIONS 3H(p, p)3H, 3He(p, p)3He et 3H(p, n)3He à Ep = 156 MeV
No full textLes sections efficaces différentielles ont été mesurées
sur des cibles gazeuses de 3H et de 3He à basse
température. Les réactions (p, p) ont été étudiées entre 16° et 178°
(CM) et la réaction (p, n) entre 109° et 178° (CM). On constate que
la section efficace de 3H(p, n)3He est de l'ordre de
quatre fois plus petite que celles de diffusion élastique. Les calculs
théoriques préliminaires ne rendent pas compte de cette différence.Differential cross sections have been measured, using
tritium and 3He gazeous targets at low temperature. (p, p) reactions
have been studied from 16° to 178° (CM) and reaction form 109°
to 178° (CM). In backward angles, the 3H(p, n)3He
cross section is about four times smaller than the elastic scattering ones.
Theoritical preliminary calculations do not explain this difference
Inertial confinement fusion fast ignition with ultra-relativistic electron beams
No full textInertial confinement fusion fast ignition at very high relativistic electron beam energy is systematically explored through a possible combination of various stopping mechanisms including strong Langmuir turbulence, elastic, and inelastic electron interactions with target particles. A specific attention is given to final state interaction through catalysis by negative pion
Inferring Time-Varying Treatment Effects from Observational Data: Lessons for Clinical Trials
No full textPersistence of the Polarization in a Fusion Process
No full textWe propose an experiment to test the persistence of the polarization in a fusion process, using a petawatt laser hitting a polarized HD target. The polarized protons and deuterons heated in the plasma induced by the laser have a significant probability to fuse producing a 3He and a γ ray or a neutron in the final state. The angular distribution of the radiated γ rays and the change in the correponding total cross section are related to the polarization persistence, but the resulting signal turns out to be weak. By comparison, the neutrons are produced hadronically with a larger cross section and are much easier to detect experimentally. A significant reduction of the cross section by parallel polarization of the deuterons is reliably predicted by the theory. Therefore, it is expected that the corresponding signal on the neutron counting rate could be seen experimentally
Polarization: A must for fusion
No full textThe complete polarization of DT fuel would increase the fusion reactivity by 50% in magnetic as well as in inertial confinements. The persistence of polarization in a fusion process could be tested, using a terawatt laser hitting a polarized HD target. The polarized deuterons heated in the plasma induced by the laser can fuse producing a 3He and a neutron in the final state. The angular distribution of the emitted neutrons and the change in the corresponding total Cross Section (CS) can sign the polarization persistence. The polarization of solid H2, D2 or T2 Hydrogen isotopes is very difficult. However, it has been possible to polarize HD, a hetero-molecular form of Hydrogen, by static polarization, at very low temperature and very high field. The radioactivity of DT molecules forbids there high polarization by the static method, therefore one has to develop the Dynamic Nuclear Polarization (DNP) by RF transitions. The DNP of HD has been investigated in the past. The magnetic properties of HD and DT molecules are very similar, it is therefore expected that any polarization result obtained with HD could be extrapolated to DT
- …
