Remaining life assessment of welded pipes containing cracks

The presence of flaws, their size and location in the welded region affects the safe service life of pressure pipes operating at elevated temperature. A remaining life assessment was required to determine the probable remaining safe life of pressure pipes in a high-temperature steam distribution system in which crack-like defects had been identified in many welds. The crack-like defects indicated by NDE lacked the required information to fully identify their locations within the pipe wall. The effect of not knowing complete details of the location of the identified cracks was studied by considering a 360° circumferential crack with initial radial dimension a₀. The crack positions evaluated were: an internal surface crack, an external surface crack, and embedded cracks at various distances from the internal wall of the pipe. Crack growth was modeled using time-dependent fracture mechanics and a newly developed computer code.     

Effect of Silicon Substitution on the Sintering and Microstructure of Hydroxyapatite

The substitution of between 0 and 1.6 wt% silicon (Si-HA) in hydroxyapatite (HA) inhibited densification at low temperatures (1000°–1150°C), with these effects being more significant as the level of silicon substitution was increased. For higher sintering temperatures (1200°–1300°C), the sintered densities of HA and Si-HA compositions were comparable. Examination of the ceramic microstructures by scanning electron microscopy (SEM) showed that silicon substitution also inhibited grain growth at higher sintering temperatures (1200°–1300°C). The negative effect of silicon substitution on the sintering of HA at low temperatures (1000°–1150°C) was reflected in the hardness values of the ceramics. However, for higher sintering temperatures, e.g., 1300°C, where sintered densities were comparable, the hardness values of Si-HA compositions were equal to or greater than that of HA, reflecting the smaller grain sizes observed for the former.     

Study on phosphate and sulphide capacities of CaO-CaCl2 slags

Experiments were carried out at 1175–1350°C to study the phosphate capacity of CaO-CaCl₂ slags and the sulphide capacity was calculated according to the correlation between the two capacities. At 1200°C the logarithm of the phosphate capacity increased from 24.5 to 26.5 with increasing CaO mole fraction from 0 to 0.22 in the slags and it decreased with increasing temperature. Sulphide capacity increased both with increasing CaO mole fraction and temperature. A good linear correlation was found between slag carbonate capacity and phosphate capacity as well as sulphide capacity. Optical basicity was used to evaluate the property of the CaO-CaCl₂ slag in the present study. The value of optical basicity of CaCl₂ is established as 0.63. The correlations of optical basicity with above mentioned three capacities were found to be linear.     

Fast and accurate NURBS fitting for reverse engineering

Fast and accurate fitting of non-uniform rational B-spline (NURBS) curves and surfaces through large sets of measured data is an important problem in applications such as reverse engineering and geometric modelling. This paper presents a method for realising significant improvements in the computational efficiency of this task. The basic idea is that the sparsity structures of the relevant matrices that are specific to the problem of NURBS fitting can be precisely defined and that full exploitation of these structures leads to significant savings in both computational and storage requirements. These savings allow for a large number of control points to be used in order to define the surface and consequently to improve the accuracy of shape representation. The achieved computational complexity is linear in both the number of measured points and the number of control points while the storage requirements of the algorithm are linear with the number of control points only. The complexity analysis, as well as the analysis of actual running times is presented. The results demonstrate that, using this approach, highly complex shapes may be modelled accurately with a single NURBS surface.     

Anisotropy of Charge Transport in a Uniaxially Aligned and Chain‐Extended,High‐Mobility,Conjugated Polymer Semiconductor

Charge transport in the ribbon phase of poly(2,5‐bis(3‐alkylthiophen‐2‐yl)thieno[3,2‐b]thiophene) (PBTTT)—one of the most highly ordered, chain‐extended crystalline microstructures available in a conjugated polymer semiconductor—is studied. Ribbon‐phase PBTTT has previously been found not to exhibit high carrier mobilities, but it is shown here that field‐effect mobilities depend strongly on the device architecture and active interface. When devices are constructed such that the ribbon‐phase films are in contact with either a polymer gate dielectric or an SiO₂ gate dielectric modified by a hydrophobic, self‐assembled monolayer, high mobilities of up to 0.4 cm² V^?1 s^?1 can be achieved, which is comparable to those observed previously in terrace‐phase PBTTT. In uniaxially aligned, zone‐cast films of ribbon‐phase PBTTT the mobility anisotropy is measured for transport both parallel and perpendicular to the polymer chain direction. The mobility anisotropy is relatively small, with the mobility along the polymer chain direction being higher by a factor of 3–5, consistent with the grain size encountered in the two transport directions.     

Stimulus duration, neural adaptation, and sweep visual evoked potential acuity estimates

PURPOSE: Results in several studies have suggested that the visual evoked potential (VEP) amplitude can vary with stimulus duration. The purpose of this study was to determine whether acuity estimates obtained by extrapolation of the sweep VEP are altered by this adaptation effect. METHODS: Sweep VEP data were obtained from 16 healthy observers under binocular viewing conditions. Data were acquired with a commercially available VEP unit using standard electrode recording techniques. Three sweeps (high spatial frequencies, medium spatial frequencies, and low spatial frequencies) were run. The subjects' visual acuity at the monitor distance was 6/6 for the high spatial frequency sweep. For the medium and low spatial frequency sweeps, the subjects were dioptrically blurred to 6/15 (medium spatial frequencies) or 6/30 (low spatial frequencies) at the monitor distance. Each sweep consisted of six spatial frequencies (contrast 80%; temporal frequency (TF) = 7.5 Hz; screen luminance = 100 candela [cd]/m2). For each spatial frequency, the stimulus duration was 8 seconds, partitioned into 1-second bins. A minimum of eight sweeps were obtained per subject. An acuity estimate was obtained for each second's data by fitting a line to the high spatial frequencies (excluding noise) and extrapolating this line to the x-axis. With this technique, estimates could not be obtained for 29 of 384 possible acuities. RESULTS: The sweep VEP acuities for the 16 subjects did not change significantly over the 8 seconds of data collection for the high, medium, or low spatial frequency sweep (repeated measures analysis of variance [ANOVA]: high, P = 0.25; medium, P = 0.50; low, P = 0.23). In any given subject, there was a 1- to 2-octave range in acuity estimates over the 8 seconds of stimulus presentation (high, 1.23+/-0.417 octaves; medium, 1.41+/-0.593 octaves; low, 1.52+/-0.475 octaves; mean +/- SD). CONCLUSIONS: These results suggest that there is not a significant change in sweep VEP acuity estimates over an 8-second stimulus presentation. Thus, neural adaptation does not significantly affect the clinical use of the sweep VEP.     

A preliminary study of the prognostic role of electromyography in laryngeal paralysis

Confidence in the reliability of laryngeal electromyography to predict recovery is critical if this tool is to be used to select the type and timing of surgical intervention. The characteristics of electromyography of 14 patients with unilateral vocal fold paralysis were assessed to determine which factor or combination of factors would be most useful in determining prognosis. We examined the duration, amplitude, waveform morphology, root-mean-square, and time interval from onset to electromyography recording. The results supported the concept that electromyography recordings are valuable in determining prognosis if performed before 6 months and preferably within 6 weeks of onset of laryngeal paralysis. A positive prognosis for laryngeal recovery was indicated when the following electromyography features were present in the immobile vocal fold: (1) normal motor unit waveform morphology, (2) overall electromyography activity characterized by a root-mean-square value greater than 40 microV in any one task, and (3) no electrical silence during voluntary tasks. On the basis of this criteria our overall correct prognostic rate was 89%.     

Effect of novel mixed ETA/ETB antagonists on responses to ET-1 in human small muscular pulmonary arteries

Selective ETA and ETB receptor antagonists do not fully inhibit responses to ET-1 in human small pulmonary arteries. Here, we have compared the influence of the novel mixed ETA/ETB antagonists SB/217242, SB/234551 and SB/209670 on ET-1-mediated vasoconstriction in these vessels. ET-1 was a potent vasoconstrictor (pEC50: 8.14+/-0.05, n=5) and the concentration-response curve to ET-1 was biphasic in nature. All three mixed antagonists (1 microM) inhibited the responses to ET-1, abolishing the biphasic form of the concentration response curve. The order of potency was SB 209670>SB 234551>/=SB 217242 with estimated pKb values of 8.0+/-0.20, 6.8+/-0.17 and 6. 6+/-0.11 respectively (n=3-5).     

A note on first-order projections and games

We show how the fact that there is a first-order projection from the problem transitive closure (TC) to some other problem Ω enables us to automatically deduce that a natural game problem, , whose instances are labelled instances of Ω, is complete for PSPACE (via log-space reductions). Our analysis is strongly dependent upon the reduction from TC to Ω being a logical projection in that it fails should the reduction be, for example, a log-space reduction or a quantifier-free first-order translation.     

Associating versus proposing or associating what we propose: Comment on Gawronski and Bodenhausen (2006).

This commentary on the article by B. Gawronski and G. V. Bodenhausen (see record 2006-10465-003) highlights the strengths of the associative-propositional evaluation model. It then describes problems in proposing a qualitative separation between propositional and associative processes. Propositional processes are instead described as associative. Propositions are ordered associations, whereas many other associations do not depend on the order of the involved elements. Implications of this alternative definition for the phenomenology of thought and for social psychology are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)