Superconducting UCN Polarizer for a New EDM Spectrometer
A test experiment has shown that the number of ultracold neutrons (UCN) of one polarization state, transmitted through a 100 μm Al foil when placed in a 5 T magnetic field, is greater by 3.8 times. The increased transmission is due to the higher velocity of the UCN passing through the foil.
Towards a new measurement of the neutron electric dipole moment
Precision measurements of particle electric dipole moments (EDMs) provide extremely sensitive means to search for non-standard mechanisms of T (or CP) violation. For the neutron EDM, the upper limit has been reduced by eight orders of magnitude in 50 years thereby excluding several CP violation scenarios. We report here on a new effort aiming at improving the neutron EDM limit by two orders of magnitude, down to a level of 3 × 10−28 e·cm. The two central elements of the approach are the use of the higher densities which will be available at the new dedicated spallation UCN source at the Paul Scherrer Institute, and the optimization of the in-vacuum Ramsey resonance technique, with storage chambers at room temperature, to reach new limits of sensitivity.
Centrifuge modelling of effects of shield tunnels on existing tunnels in soft clay
With the rapid development of the subway network,the phenomena of shield tunnels going across the adjacent tunnels are becoming more and more common.The interaction between shield tunneling and nearby tunnels is more complicated than the ordinary shield tunneling in intact soil strata.Based on the project of Shanghai Bund Passage crossing Metro Line 2,the method of centrifuge modeling together with the field measurement is employed to study the effects shield tunneling on nearby strata and existing tunnels.In centrifugal model tests,the effects simulation techniques considering the unloading of excavation,ground loss and grouting are developed to analyze the longitudinal settlement of the shield tunnel and the existing tunnel induced by the shield tunneling.Besides,the deformation distribution and settlement curves of the existing tunnels during shield construction are studied by using the monitoring data.