Eddy current testing of AGR fuel cladding

The scope of the presented study was to investigate feasibility of Eddy Current Testing (ECT) for detection in storage of inter-granular attack (IGA) cracking and general clad thinning of irradiated fuel cladding from Advanced Gas-cooled Reactors (AGR). The impact of the storage environment, particularly the effect of immersion in water compared to measurements in air, has also been investigated. A miniature EC probe was developed to induce eddy currents in a pin and to read out EC response. The transducer was robotically moved along the AGR pin and multi-frequency EC responses were acquired using a spectrum analyser. Main results of the experimental investigation are the following: even very small artificial defects such as short EDM notches of depth of 100μm produce distinguishable EC response; localised clad thinning of depth of 100μm and above produces considerable EC response levels; effect of water environment on the EC response is negligible; effect of anti-stacking grooves on the EC response is considerable

Robotic ultrasonic testing of AGR fuel cladding

The purpose of the presented work was to undertake experimental trials to demonstrate the potential capabilities of an in-situ robotic ultrasonic scanning technique for measuring and monitoring loss of the cladding wall thickness in fuel pins of Advanced Gas-cooled Reactors (AGR) using inactive (i.e. non-radioactive) samples. AGR fuel pins are stainless steel cylindrical ribbed pipes of length circa of 1000 mm, inner diameter of the rod being circa 15 mm and wall thickness of circa 300µm. Spent AGR fuel pins are stored in a water pond and thus may be prone to corrosion and stresscorrosion cracking under adverse conditions. An ultrasonic immersion transducer with central frequency of 25MHz was used to measure wall thickness of the AGR fuel cladding using a frequency domain technique. Cylindrical ultrasonic scan of the samples 2 was performed using industrial robotic arm KUKA KR 5 arc HW. Also, very short (2.5mm long) and shallow (100µm in depth) crack-like defects were detected using time-domain technique

A Model for the Elasticity of Compressed Emulsions

We present a new model to describe the unusual elastic properties of compressed emulsions. The response of a single droplet under compression is investigated numerically for different Wigner-Seitz cells. The response is softer than harmonic, and depends on the coordination number of the droplet. Using these results, we propose a new effective inter-droplet potential which is used to determine the elastic response of a monodisperse collection of disordered droplets as a function of volume fraction. Our results are in excellent agreement with recent experiments. This suggests that anharmonicity, together with disorder, are responsible for the quasi-linear increase of $G$ and $\Pi$ observed at $\varphi_c$.Comment: RevTeX with psfig-included figures and a galley macr

Risk Tolerance, Self-Interest, and Social Preferences

We use an experimental method to investigate whether systematic relationships exist across distinct aspects of individual preferences: risk aversion in monetary outcomes, altruism in a twoperson context, and social preferences in a larger group context. Individual preferences across these three contexts are measured, and there is no possibility for risk sharing, wealth effects, or updating expectations of the population choices. We find that social preferences are related to demographic variables, including years of education, gender, and age. Perhaps most importantly, self allocation in a two-person dictator game is related to social preferences in a group context. Participants who are more generous in a dictator game are more likely to vote against their selfinterest in a group decision-making task which we interpret to be expressions of social preferences

A Search for Dark Higgs Bosons

Recent astrophysical and terrestrial experiments have motivated the proposal of a dark sector with GeV-scale gauge boson force carriers and new Higgs bosons. We present a search for a dark Higgs boson using 516 fb-1 of data collected with the BABAR detector. We do not observe a significant signal and we set 90% confidence level upper limits on the product of the Standard Model-dark sector mixing angle and the dark sector coupling constant.Comment: 7 pages, 5 postscript figures, published version with improved plots for b/w printin

Search for anomalous t t-bar production in the highly-boosted all-hadronic final state

A search is presented for a massive particle, generically referred to as a Z', decaying into a t t-bar pair. The search focuses on Z' resonances that are sufficiently massive to produce highly Lorentz-boosted top quarks, which yield collimated decay products that are partially or fully merged into single jets. The analysis uses new methods to analyze jet substructure, providing suppression of the non-top multijet backgrounds. The analysis is based on a data sample of proton-proton collisions at a center-of-mass energy of 7 TeV, corresponding to an integrated luminosity of 5 inverse femtobarns. Upper limits in the range of 1 pb are set on the product of the production cross section and branching fraction for a topcolor Z' modeled for several widths, as well as for a Randall--Sundrum Kaluza--Klein gluon. In addition, the results constrain any enhancement in t t-bar production beyond expectations of the standard model for t t-bar invariant masses larger than 1 TeV.Comment: Submitted to the Journal of High Energy Physics; this version includes a minor typo correction that will be submitted as an erratu

Search for the standard model Higgs boson in the H to ZZ to 2l 2nu channel in pp collisions at sqrt(s) = 7 TeV

A search for the standard model Higgs boson in the H to ZZ to 2l 2nu decay channel, where l = e or mu, in pp collisions at a center-of-mass energy of 7 TeV is presented. The data were collected at the LHC, with the CMS detector, and correspond to an integrated luminosity of 4.6 inverse femtobarns. No significant excess is observed above the background expectation, and upper limits are set on the Higgs boson production cross section. The presence of the standard model Higgs boson with a mass in the 270-440 GeV range is excluded at 95% confidence level.Comment: Submitted to JHE

Measurement of the t t-bar production cross section in the dilepton channel in pp collisions at sqrt(s) = 7 TeV

The t t-bar production cross section (sigma[t t-bar]) is measured in proton-proton collisions at sqrt(s) = 7 TeV in data collected by the CMS experiment, corresponding to an integrated luminosity of 2.3 inverse femtobarns. The measurement is performed in events with two leptons (electrons or muons) in the final state, at least two jets identified as jets originating from b quarks, and the presence of an imbalance in transverse momentum. The measured value of sigma[t t-bar] for a top-quark mass of 172.5 GeV is 161.9 +/- 2.5 (stat.) +5.1/-5.0 (syst.) +/- 3.6(lumi.) pb, consistent with the prediction of the standard model.Comment: Replaced with published version. Included journal reference and DO

Combined search for the quarks of a sequential fourth generation

Results are presented from a search for a fourth generation of quarks produced singly or in pairs in a data set corresponding to an integrated luminosity of 5 inverse femtobarns recorded by the CMS experiment at the LHC in 2011. A novel strategy has been developed for a combined search for quarks of the up and down type in decay channels with at least one isolated muon or electron. Limits on the mass of the fourth-generation quarks and the relevant Cabibbo-Kobayashi-Maskawa matrix elements are derived in the context of a simple extension of the standard model with a sequential fourth generation of fermions. The existence of mass-degenerate fourth-generation quarks with masses below 685 GeV is excluded at 95% confidence level for minimal off-diagonal mixing between the third- and the fourth-generation quarks. With a mass difference of 25 GeV between the quark masses, the obtained limit on the masses of the fourth-generation quarks shifts by about +/- 20 GeV. These results significantly reduce the allowed parameter space for a fourth generation of fermions.Comment: Replaced with published version. Added journal reference and DO