Test of ID carbon-carbon composite prototype tiles for the SPIDER diagnostic calorimeter

Additional heating will be provided to the thermonuclear fusion experiment ITER by injection of neutral beams from accelerated negative ions. In the SPIDER test facility, under construction at Consorzio RFX in Padova (Italy), the production of negative ions will be studied and optimised. To this purpose the STRIKE (Short-Time Retractable Instrumented Kalorimeter Experiment) diagnostic will be used to characterise the SPIDER beam during short operation (several seconds) and to verify if the beam meets the ITER requirement regarding the maximum allowed beam non-uniformity (below \ub110%). The most important measurements performed by STRIKE are beam uniformity, beamlet divergence and stripping losses. The major components of STRIKE are 16 1D-CFC (Carbon matrix-Carbon Fibre reinforced Composite) tiles, observed at the rear side by a thermal camera. The requirements of the 1D CFC material include a large thermal conductivity along the tile thickness (at least 10 times larger than in the other directions); low specific heat and density; uniform parameters over the tile surface; capability to withstand localised heat loads resulting in steep temperature gradients. So 1D CFC is a very anisotropic and delicate material, not commercially available, and prototypes are being specifically realised. This contribution gives an overview of the tests performed on the CFC prototype tiles, aimed at verifying their thermal behaviour. The spatial uniformity of the parameters and the ratio between the thermal conductivities are assessed by means of a power laser at Consorzio RFX. Dedicated linear and non-linear simulations are carried out to interpret the experiments and to estimate the thermal conductivities; these simulations are described and a comparison of the experimental data with the simulation results is presented

Isoscalar off-shell effects in threshold pion production from pd collisions

We test the presence of pion-nucleon isoscalar off-shell effects in the $pd\to \pi^+ t$ reaction around the threshold region. We find that these effects significantly modify the production cross section and that they may provide the missing strength needed to reproduce the data at threshold.Comment: 6 pages, REVTeX, twocolumn, including 3 figures (Postscript), uses psfig, updated and extended versio

Why is the three-nucleon force so odd?

By considering a class of diagrams which has been overlooked also in the most recent literature on three-body forces, we extract a new contribution to the three-nucleon interaction which specifically acts on the triplet odd states of the two nucleon subsystem. In the static approximation, this 3N-force contribution is fixed by the underlying 2N interaction, so in principle there are no free parameters to adjust. The 2N amplitude however enters in the 3NF diagram in a form which cannot be directly accessed or constrained by NN phase-shift analysis. We conclude that this new 3N-force contribution provides a mechanism which implies that the presence of the third nucleon modifies the p-wave (and possibly the f-wave) components of the 2N subsystem in the triplet-isotriplet channels.Comment: 10 Pages, 7 figures, RevTeX, twocolumn, epsf (updated version with minor changes

The one-pion-exchange three-nucleon force and the AyA_y puzzle

We consider a new three-nucleon force generated by the exchange of one pion in the presence of a 2N correlation. The underlying irreducible diagram has been recently suggested by the authors as a possible candidate to explain the puzzle of the vector analyzing powers $A_y$ and $iT_{11}$ for nucleon-deuteron scattering. Herein, we have calculated the elastic neutron-deuteron differential cross section, $A_y$, $iT_{11}$, $T_{20}$, $T_{21}$, and $T_{22}$ below break-up threshold by accurately solving the Alt-Grassberger-Sandhas equations with realistic interactions. We have also studied how $A_y$ evolves below 30 MeV. The results indicate that this new 3NF diagram provides one possible additional contribution, with the correct spin-isospin structure, for the explanation of the origin of this puzzle.Comment: revised version: We have also studied how Ay evolves below 30 MeV, 4 Pages (twocolumn), 2 figures, uses psfig, RevTe

Practical approximation scheme for the pion dynamics in the three-nucleon system

We discuss a working approximation scheme to a recently developed formulation of the coupled piNNN-NNN problem. The approximation scheme is based on the physical assumption that, at low energies, the 2N-subsystem dynamics in the elastic channel is conveniently described by the usual 2N-potential approach, while the explicit pion dynamics describes small, correction-type effects. Using the standard separable-expansion method, we obtain a dynamical equation of the Alt-Grassberger-Sandhas (AGS) type. This is an important result, because the computational techniques used for solving the normal AGS equation can also be used to describe the pion dynamics in the 3N system once the matrix dimension is increased by one component. We have also shown that this approximation scheme treats the conventional 3N problem once the pion degrees of freedom are projected out. Then the 3N system is described with an extended AGS-type equation where the spin-off of the pion dynamics (beyond the 2N potential) is taken into account in additional contributions to the driving term. These new terms are shown to reproduce the diagrams leading to modern 3N-force models. We also recover two sets of irreducible diagrams that are commonly neglected in 3N-force discussions, and conclude that these sets should be further investigated, because a claimed cancellation is questionable.Comment: 18 pages, including 5 figures, RevTeX, Eps

Comparison between two methods of solution of coupled equations for low-energy scattering

Cross sections from low-energy neutron-nucleus scattering have been evaluated using a coupled channel theory of scattering. Both a coordinate-space and a momentum-space formalism of that coupled-channel theory are considered.A simple rotational model of the channel interaction potentials is used to find results using two relevant codes, ECIS97 and MCAS, so that they may be compared. The very same model is then used in the MCAS approach to quantify the changes that occur when allowance is made for effects of the Pauli principle.Comment: 6 pages, 3 figure

A genetic algorithm for resizing and sampling reduction of non-stationary soil chemical attributes optimizing spatial prediction

Aim of study: To evaluate the influence of the parameters of the geostatistical model and the initial sample configuration used in the optimization process; and to propose and evaluate the resizing of a sample configuration, reducing its sample size, for simulated data and for the study of the spatial variability of soil chemical attributes under a non-stationary with drift process from a commercial soybean cultivation area.Area of study: Cascavel, BrazilMaterial and methods: For both, the simulated data and the soil chemical attributes, the Genetic Algorithm was used for sample resizing, maximizing the overall accuracy measure.Main results: The results obtained from the simulated data showed that the practical range did not influence in a relevant way the optimization process. Moreover, the local variations, such as variance or sampling errors (nugget effect), had a direct relationship with the reduction of the sample size, mainly for the smaller nugget effect. For the soil chemical attributes, the Genetic Algorithm was efficient in resizing the sampling configuration, since it generated sampling configurations with 30 to 35 points, corresponding to 29.41% to 34.31% of the initial configuration, respectively. In addition, comparing the optimized and initial configurations, similarities were obtained regarding spatial dependence structure and characterization of spatial variability of soil chemical attributes in the study area.Research highlights: The optimization process showed that it is possible to reduce the sample size, allowing for lesser financial investments with data collection and laboratory analysis of soil samples in future experiments

Analysis of Sub-threshold Short Gamma-ray Bursts in Fermi GBM Data

The Fermi Gamma-ray Burst Monitor (GBM) is currently the most prolific detector of Gamma-Ray Bursts (GRBs). Recently the detection rate of short GRBs (SGRBs) has been dramatically increased through the use of ground-based searches that analyze GBM continuous time tagged event (CTTE) data. Here we examine the efficiency of a method developed to search CTTE data for sub-threshold transient events in temporal coincidence with LIGO/Virgo compact binary coalescence triggers. This targeted search operates by coherently combining data from all 14 GBM detectors by taking into account the complex spatial and energy dependent response of each detector. We use the method to examine a sample of SGRBs that were independently detected by the Burst Alert Telescope on board the Neil Gehrels Swift Observatory, but which were too intrinsically weak or viewed with unfavorable instrument geometry to initiate an on-board trigger of GBM. We find that the search can successfully recover a majority of the BAT detected sample in the CTTE data. We show that the targeted search of CTTE data will be crucial in increasing the GBM sensitivity, and hence the gamma-ray horizon, to weak events such as GRB 170817A. We also examine the properties of the GBM signal possibly associated with the LIGO detection of GW150914 and show that it is consistent with the observed properties of other sub-threshold SGRBs in our sample. We find that the targeted search is capable of recovering true astrophysical signals as weak as the signal associated with GW150914 in the untriggered data.Comment: 10 pages, 9 figures, 1 table, submitted to Ap