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Effect of residual stresses of multiple welding repairs on API 5L X52 pipeline steel on stress corrosion cracking (SCC) in a simulated acidic soil solution was studied. Four conditions of repairs of the girth weld were evaluated. The residual stresses were measured through X-ray diffraction (XRD) on the internal side of the pipe in longitudinal and circumferential direction. The circumferential and longitudinal residual stresses values are compressive on the inner surface of the welding joints. The highest residual stresses were measured in the hoop direction reaching values of about 98% of the yielding strength (360 MPa). It was observed that its magnitude increases as move away from weld center line. The effect of residuals stresses in the SCC susceptibility of X52 pipeline steel was evaluated through slow strain rate tests (SSRT) in a simulated acidic soil solution. Relation between mechanical properties obtained from SSRT and residual stresses on the SCC susceptibility was analyzed. Results of SCC index taking account the ratios obtained from the mechanical properties of the welding joints evaluate, showed good SCC resistance in acidic soil solution at low pH. Scanning electron microscopy (SEM) observations showed that the region with high residual stresses prior to generate cracks in the steel due to the combination of soil solution and the strain exerted, should favor pitting formation and not cracking.
In this work slow strain rate tests (SSRT) were used for the evaluation of API 5L X60 in contact with a simulated soil solution called NS4 in order to evaluate stress corrosion cracking (SCC) susceptibility. SSRT were carried out in NS4 solution at room temperature to simulate dilute ground water that has been found to be associated with SCC of low carbon steel pipelines. A strain rate of 1x10-6 sec-1 was used. According to the analysis of SSRT results, the X60 pipeline steel is highly resistant to SCC at the conditions studied. A combine fracture type it was observed: ductile and brittle with a transgranular appearance. Some pits close to the fracture zone were observed. The failure process and mechanism of X60 steel in NS4 solution are controlled by anodic dissolution and hydrogen embrittlement which was revealed with the internal cracks observed in the surface fracture. There is a relation between the strength of the steel and the SCC susceptibility, thus, increasing strength in the steel, the SCC susceptibility increases as a function of the pH solution used.
Manufacturing of high dimension steel rings impose several technological challenges. The lack of understanding of the principles and practices of quenching can result in inadequate hardness, excessive distortion or scrapping of costly machined components. This paper presents the results of an analytical study of the parameters of the quenching operation, among them the fluid dynamics of the agitation in the quenching media. Velocity components of the fluid were measured using an anemometer inside the quenching tank. Uniformity of agitation is compared with a Computational Fluid Dynamics (CFD) simulation. The CFD results revealed the impact of quench tank design, configuration and operation of impellers.
We present the propagation properties of Dirac-electrons in multilayered Period-Doubling (MPDGS) and Silver-Mean (MSMGS) graphene structures. The multilayered graphene structures are built arranging breaking and non-breaking symmetry substrates such as SiC and SiO2 following a given quasirregular substitution rule locating on them a graphene sheet. We have implemented the Transfer Matrix technique to calculate the transmittance of these multilayered graphene structures. This technique allows us to analyze readily the main differences of the transmission properties between MPDGS and MSMGS.
It has become widely accepted that cognitive deficits in schizophrenia are related to functional outcome. However, it remains to be seen whether these associations are relevant for predicting which cases will have a global functional recovery. In this study, we attempt to determine whether global functional recovery (integrating social and occupational outcomes) after first-episode schizophrenia (FES) can be predicted by cognitive variables.
A total of 131 FES patients with functional deficits (n=97) and functional recovery (n=34) as determined at 1-year follow-up were examined. Neuropsychological, sociodemographic, pre-morbid and clinical data at baseline were analysed using independent groups comparisons and a logistic regression method.
Sustained attention and negative symptoms emerged as significant predictors of good global functional outcome. Although the model revealed a high accuracy (91%) in the classification of patients with functional deficits, it was unacceptably low (26%) in the classification of patients with global functional recovery.
The limitations found in the prediction of a favourable global functional outcome may well be an indication for a need to address the role of other factors not commonly included in longitudinal studies of long-term outcomes in schizophrenia.
Cannabis use appears to be a risk factor for schizophrenia. Moreover, cannabis abusers show impaired decision-making capacities, linked to the orbitofrontal cortex (OFC). Although there is substantial evidence that first-episode schizophrenia patients show impairments in cognitive tasks associated with the dorsolateral prefrontal cortex (DLPFC), it is not clear whether decision making is impaired at schizophrenia onset. In this study, we examined the association between antecedents of cannabis abuse and cognitive impairment in cognitive tasks associated with the DLPFC and the OFC in a sample of first-episode patients with schizophrenia-spectrum disorders.
One hundred and thirty-two patients experiencing their first episode of a schizophrenia-spectrum psychosis were assessed with a cognitive battery including DLPFC-related tasks [backward digits, verbal fluency (FAS) and the Trail Making Test (TMT)] and an OFC-related task [the Iowa Gambling Task (GT)]. Performance on these tasks was compared between patients who had and had not abused cannabis before their psychosis onset.
No differences were observed between the two groups on the performance of any of the DLPFC-related tasks. However, patients who had abused cannabis before their psychosis onset showed a poorer total performance on the gambling task and a lower improvement on the performance of the task compared to no-abusers.
Pre-psychotic cannabis abuse is associated with decision-making impairment, but not working memory and executive function impairment, among first-episode patients with a schizophrenia-spectrum psychosis. Further studies are needed to examine the direction of causality of this impairment; that is, does the impairment make the patients abuse cannabis, or does cannabis abuse cause the impairment?
An indirect observation of 90° domain reversal under the influence of a poling field process was undertaken by an x-ray diffraction study in the Pb0.88Eu0.08Ti1™y MnyO3 (y = 0, 0.01, 0.02, and 0.03) piezoelectric anisotropic system. The optimum condition kp → 0 was achieved for y = 0.02 composition. A large percentage of 90° domain rotation was necessary, but not a sufficient condition for the ultrahigh electromechanical anisotropy manifestation. A large microstrain originated by structural defects in unpoled samples seemed to play a crucial role in the attainment of this piezoelectric anisotropy. A breaking in the translational periodicity due to induced vacancy in Pb and O sites by Eu3+ and Mn2+ substitutions was manifested in the nonuniform variance of the tetragonality (c/a), the large microstrain, and the detriment of crystallinity observed.
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