Sensor placement for structural damage detection with modal data

A new method is presented for prioritizing sensor locations for structural health monitoring (SHM). In view of the needs of SHM and damage detection,sensor locations are optimized for the purpose of both sensitivity for local damages and independence of the target mode. However,the two different optimization criterions lead to an inconsistency of the optimal result. Considering the structural response changes that result from damage,the relationship between the structural response and damage is deduced from the structural motion equation by a quasi-analytical mode. Based on the harmony between damage identifiability and mode observability,an object function is set up,including the information of mode independence and damage sensitivity. Utilizing the technique of singular value decomposition,an interior algorithm for the optimum sensor placement is proposed with the multiple objective criterions of minimizing the condition number of coefficient matrix and maximizing the fisher information matrix. A numerical example shows that this approach can effectively avoid the contradiction between the two different optimization criterions. Comparing with the result of single object,the result of damage detection from the optical sensor locations is much more accurate.     

Hard pure carbon coatings from a voltage-assisted arc

A simple apparatus is described that produces hard carbon coatings by accelerating ions produced by a carbon arc operating in vacuum. Coatings up to 1.1 μm thick have been produced on a variety of metals and semiconductors.     

Choice of scatterer crystals to optimize the performance of Compton polarimeters

The response of two-crystal Compton γ-ray polarimeters is compared in various 90° scattering geometries. The main factors affecting the quality of the data are the size of the scatterer crystal and its Compton profile.     

Cryogenic test of a superconducting half-wave resonator for the acceleration of heavy ions

We present the results of cryogenic tests on a superconducting half-wave resonator for the acceleration of heavy ions. The resonator was built out of OFHC copper and electroplated with 1.5 μm of Pb without chemical polish of the Pb surface. Measured properties include a low level Q of 4 × 10⁸ and a power dissipation of 6 W at 4 MV/m giving an energy gain of 1 MV per unit change to a particle of velocity 0.16 c.     

Temperature dependence of BGO-CsI(Tl) phoswich detector properties

We have studied the variations of the performances, and particularly the discrimination efficiency, of a BGO-CsI(Tl) phoswich detector in the temperature range 2.5–40°C.The scintillation decay time evaluation has been carried out by means of a double constant fraction discriminator and a time to amplitude converter on 1 μs shaped pulses. Good discrimination between BGO and CsI(Tl) events has been obtained over the whole temperature range, even though small efficiency variations are present because of the relative displacement of the acceptance window of the discriminator due to the decay time dependence on temperature. A criterium to minimize this effect, useful in particular for the BGO-CsI(Tl) phoswich, has been developed.     

A detection system using drift chambers for the SPES4 spectrometer at Laboratoire National Saturne

We describe the “drift chamber” detection setup of SPES4, the 4 GeV/c spectrometer at Laboratoire National Saturne. The particle identification is performed by combining magnetic rigidity selection with energy loss and time of flight measurements. This allows to separate analysed isotopes from Z = 1 to at least Z = 10 up to a rigidity of 4 GeV/c. A charge resolution of ΔZ_rms = 0.1 and a time resolution of Δt_rms = 120 ps for ¹⁸Ne at about 3 GeV/c per Z are easily obtained. Two sets of multiwire drift chambers are used to measure and reconstruct the particle trajectories at the output of the system. A position resolution better than Δx_rms = 160 μm can be achieved in the focal plane. This corresponds to a momentum resolution of Δδ_rms = 0.22 × 10⁻⁴. The performances of SPES4 (Δδ_rms = 2.2 × 10⁻⁴) can then be wholly exploited.     

The preparation and characterization of a Ni-3 wt.% U reference fission product source for super phenix

The fabrication and quality control of Ni-3 wt.% U (93% ²³⁵U) alloy rods (diameter: 8 mm, total length: 8 m) used as a reference fission product source (RFPS) are described. This RFPs is needed for the calibration of the fuel element rupture detector which is used for the continuous monitoring of the delayed neutron activity in the primary sodium of the Super Phenix fast neutron reactor. Special care was taken to obtain a sufficient alloy purity, a bright surface finish and a homogeneous ²³⁵U content on the surface of the rods. Finally the usefulness of the RFPS in Super Phenix has been demonstrated.     

Estimation of shielding failure number of transmission lines for different trace configurations using leader progression analysis

The electrogeometric model (EGM) is a technique used for analyzing the termination of lightning flashes on transmission lines and masts, etc. When using the EGM for modeling the lightning stroke to transmission lines, the power line has normally been represented by a set of horizontal wire and both the sag of the wire, the existence of the towers and effect of uneven way have been ignored. This approach has serious short comings including inability to determine the percentage of the strokes terminating on the towers, failure to correctly predict the effect of height, and giving an approximate value for the number of collected strokes. This paper presents the development of a method for estimating the shielding failure number of power transmission lines in different trace configurations by using the charge simulation method. The effects of towers, sags of conductors, and a perfectly conducting ground are represented in 3-D computation. In addition, the stepwise descending nature of a downward negative leader–streamer systems taken into account by using an appropriate progression model. Upward leader inception and propagation is also modeled utilizing critical equivalent streamer-length criterion. The method is applied to compute the shielding failure of power transmission line for different trace configurations. In this paper the 3-D method is extended by modeling the effect of sloppy trace, trees on both and one side of the transmission line with extensive simulation results. Also, in this paper the effect of variation of tree height, its distance from transmission line and the number of trees on SFN are analyzed and results are shown in curves.