The PICASSO experiment reports an improved limit for the existence of cold dark matter WIMPs interacting via spin-dependent interactions with nuclei.The experiment is installed in the Sudbury Neutrino Observatory at a depth of 2070 m. With superheated C 4 F 10 droplets as the active material, and an exposure of 1.98±0.19 kgd, no evidence for a WIMP signal was found. For a WIMP mass of 29 GeV/c 2 , limits on the spin-dependent cross section on protons of σ p = 1.31 pb and on neutrons of σ n = 21.5 pb have been obtained at 90% C.L. In both cases, some new parameter space in the region of WIMP masses below 20 GeV/c 2 has now been ruled out. The results of these measurements are also presented in terms of limits on the effective WIMP-proton and neutron coupling strengths a p and a n .

We present results of systematic studies of the radiation response of superheated liquid droplet detectors, which are used in the PICASSO dark matter search experiment. This detection technique is based on the phase transitions of superheated liquid Freon droplets dispersed and trapped in a polymerized gel. Phase transitions can be induced by nuclear recoils following particle interactions and, in particular, interactions with Weakly Interacting Massive Particles (WIMPs). These detectors are threshold devices since a minimal energy deposition is necessary to induce a phase transition and their sensitivity to various types of radiation depends strongly on the operating temperature and pressure. The sensitivity to neutrons, a-particles and g-rays was determined as a function of these operating parameters and the results are compared with simulations. In particular, we present a complete characterization of the response of detector modules already in use for a dark matter search at the SNO site to detect WIMPs and discuss possible background sources. r

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Additive manufacturing (AM) is projected to require 60,000 jobs in the UK by 2025, but there are a series of barriers to the industrial application. One of the most problematic is non-comprehensive knowledge in design for AM (DfAM). This study aims to test the effect of two undergraduate DfAM teaching approaches. A visual and audial approach (design lecture) and a kinaesthetic, problem-based learning (PBL) approach (manufacturing laboratory) were compared against technical and participant perspective criteria to assess the learning, engagement, and self-efficacy of the students. The participants were set a DfAM challenge; to redesign a bracket. The technical merits of the designs were evaluated after teaching through a design lecture alone or after a design lecture and manufacturing-laboratory. The participant’s perspective was evaluated at the end of the study. The groups who undertook both the design lecture and manufacturing laboratory showed a mean technical mark of 100% for criteria (C) 13 (“Parts have been consolidated into one part”), 91.7% for C14 (“The bracket is hollowed where possible”) and 100% for C16 (“Manufacture was successful”). These technical marks demonstrate a statistically significant increase over those of the groups who undertook the design lecture alone. The participant evaluation reinforced this result; the manufacturing laboratory was chosen more frequently in answer to questions on applicability (Q13 = 83%), preparedness (Q15 = 83%), and gaining confidence in DfAM (Q31 = 74%). This study demonstrates the importance of PBL in DfAM, both to increase technical aptitude of the student (creativity and manufacturing) and their perspective on their own learning and self-efficacy.