Probabilistic models to evaluate effectiveness of steel bridge weld fatigue retrofitting by peening

The purpose of this study was to evaluate, with two probabilistic analytical models, the effectiveness of several alternative fatigue management strategies for steel bridge welds. The investigated strategies employed, in various combinations, magnetic particle inspection, gouging and rewelding, and postweld treatment by peening. The analytical models included a probabilistic strain-based fracture mechanics model and a Markov chain model. For comparing the results obtained with the two models, the fatigue life was divided into a small, fixed number of condition states based on crack depth, similar to those often used by bridge management systems to model deterioration due to other processes, such as corrosion and road surface wear. The probabilistic strain-based fracture mechanics model was verified first by comparison with design S-N curves and test data for untreated welds. Next, the verified model was used to determine the probability that untreated and treated welds would be in each condition state in a given year; the probabilities were then used to calibrate transition probabilities for a much simpler Markov chain fatigue model. Then both models were used to simulate a number of fatigue management strategies. From the results of these simulations, the performance of the different strategies was compared, and the accuracy of the simpler Markov chain fatigue model was evaluated. In general, peening was more effective if preceded by inspection of the weld. The Markov chain fatigue model did a reasonable job of predicting the general trends and relative effectiveness of the different investigated strategies

Poly(dimethylsiloxane)-Stabilized Polymer Particles from Radical Dispersion Polymerization in Nonpolar Solvent: Influence of Stabilizer Properties and Monomer Type

Particles used in electrophoretic display applications (EPD) must possess a number of specific properties ranging from stability in a nonaqueous solvent, high reflectivity, low polydispersity, and high charge density to name but a few. The manufacture of such particles is best carried out in the solvent of choice for the EPD. This opens up new interests in the study of nonaqueous dispersion polymerization methods, which deliver polymer particles suspended in low dielectric constant solvents. We explore in this article the use of a poly(dimethylsiloxane) macromonomer for the stabilization of poly(methyl methacrylate) polymer particles in dodecane, a typical solvent of choice for EPDs. The use of this stabilizer is significant for this method as it is directly soluble in the reaction medium as opposed to traditionally used poly(12-hydroxystearic acid)-based stabilizers. Additionally, the present study serves as a baseline for subsequent work, where nonaqueous dispersion polymerization will be used to create polymer particles encapsulating liquid droplets and solid pigment particles. In this article, the influence of the macromonomer molecular weight and concentration on the properties of the synthesized particles is studied. In addition, we investigate the possibility of synthesizing polymer particles from other monomers both as a comonomer for methyl methacrylate and as the only monomer in the process. The influence of macromonomer concentration is also studied throughout all experiments

Active Damping of the E-P Instability at the Los Alamos Proton Storage Ring

A prototype of an analog, transverse (vertical) feedback system for active damping of the two-stream (e-p) instability has been developed and successfully tested at the Los Alamos Proton Storage Ring (PSR). This system was able to improve the instability threshold by approximately 30% (as measured by the change in RF buncher voltage at instability threshold). The feedback system configuration, setup procedures, and optimization of performance are described. Results of several experimental tests of system performance are presented including observations of instability threshold improvement and grow-damp experiments, which yield estimates of instability growth and damping rates. A major effort was undertaken to identify and study several factors limiting system performance. Evidence obtained from these tests suggests that performance of the prototype was limited by higher instability growth rates arising from beam leakage into the gap at lower RF buncher voltage and the onset of instability in the horizontal plane, which had no feedback

A Slow Neutron Polarimeter for the Measurement of Parity-Odd Neutron Rotary Power

We present the design, description, calibration procedure, and an analysis of systematic effects for an apparatus designed to measure the rotation of the plane of polarization of a transversely polarized slow neutron beam as it passes through unpolarized matter. This device is the neutronoptical equivalent of a crossed polarizer/analyzer pair familiar from light optics. This apparatus has been used to search for parity violation in the interaction of polarized slow neutrons in matter. Given the brightness of existing slow neutron sources, this apparatus is capable ofmeasuring a neutron rotary power of dϕ/dz = 1 × 10−7 rad/m

A Slow Neutron Polarimeter for the Measurement of Parity-Odd Neutron Rotary Power

We present the design, description, calibration procedure, and an analysis of systematic effects for an apparatus designed to measure the rotation of the plane of polarization of a transversely polarized slow neutron beam as it passes through unpolarized matter. This device is the neutron optical equivalent of a crossed polarizer/analyzer pair familiar from light optics. This apparatus has been used to search for parity violation in the interaction of polarized slow neutrons in matter. Given the brightness of existing slow neutron sources, this apparatus is capable of measuring a neutron rotary power of dϕ/dz = 1 × 10−7 rad/m

Parity violating neutron spin rotation in 4He and H

The weak interaction between nucleons leads to parity violation in various reaction observables. Neutron spin rotation, the rotation of the plane of polarization of a transversely polarized neutron beam passing through unpolarized matter, is an especially clear example of a breakdown in mirror symmetry. The Neutron Spin Rotation (NSR) Collaboration is engaged in an experimental program to observe parity-odd neutron spin rotation. We recently completed the first phase of an experiment to measure parity violating neutron spin rotation in 4He. Our result for the neutron spin rotation angle per unit length in 4He, dφ/dz = (+1.7 ± 9.1(stat.) ± 1.4(sys.)) × 10−7 rad/m, is the most sensitive search for neutron weak optical activity yet performed and represents a significant advance in precision in comparison to past measurements in heavy nuclei. This experiment was performed at the NG-6 slow neutron beamline at the National Institute of Standards and Technology (NIST) Center for Neutron Research. The systematic uncertainty is small enough to proceed to the second phase of the 4He measurement at the new NG-C slow neutron beamline under construction at NIST. The projected intensity of this beam is high enough to see parity odd neutron spin rotation in 4He and to seriously consider a future experiment to measure neutron spin rotation in hydrogen

Active Damping of the E-P Instability at the LANL PSR

A prototype of an analog, transverse (vertical) feedback system for active damping of the two-stream (e-p) instability has been developed and successfully tested at the Los Alamos National Laboratory Proton Storage Ring (PSR). This system was able to improve the instability threshold by approximately 30% (as measured by the change in RF buncher voltage at instability threshold). Evidence obtained from these tests suggests that further improvement in performance is limited by beam leakage into the gap at lower RF buncher voltage and the onset of instability in the horizontal plane, which had no feedback. Here we describe the present system configuration, system optimization, results of several recent experimental tests, and results from studies of factors limiting its performance

General anaesthetic and airway management practice for obstetric surgery in England: a prospective, multi-centre observational study

There are no current descriptions of general anaesthesia characteristics for obstetric surgery, despite recent changes to patient baseline characteristics and airway management guidelines. This analysis of data from the direct reporting of awareness in maternity patients' (DREAMY) study of accidental awareness during obstetric anaesthesia aimed to describe practice for obstetric general anaesthesia in England and compare with earlier surveys and best-practice recommendations. Consenting patients who received general anaesthesia for obstetric surgery in 72 hospitals from May 2017 to August 2018 were included. Baseline characteristics, airway management, anaesthetic techniques and major complications were collected. Descriptive analysis, binary logistic regression modelling and comparisons with earlier data were conducted. Data were collected from 3117 procedures, including 2554 (81.9%) caesarean deliveries. Thiopental was the induction drug in 1649 (52.9%) patients, compared with propofol in 1419 (45.5%). Suxamethonium was the neuromuscular blocking drug for tracheal intubation in 2631 (86.1%), compared with rocuronium in 367 (11.8%). Difficult tracheal intubation was reported in 1 in 19 (95%CI 1 in 16-22) and failed intubation in 1 in 312 (95%CI 1 in 169-667). Obese patients were over-represented compared with national baselines and associated with difficult, but not failed intubation. There was more evidence of change in practice for induction drugs (increased use of propofol) than neuromuscular blocking drugs (suxamethonium remains the most popular). There was evidence of improvement in practice, with increased monitoring and reversal of neuromuscular blockade (although this remains suboptimal). Despite a high risk of difficult intubation in this population, videolaryngoscopy was rarely used (1.9%)