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BackgroundWith the development of nuclear medicine, the amount of medical radioactive waste increase rapidly. The radioactivity of nuclides in medical radioactive liquid waste must be monitored to meet the relevant standards before discharge of the radioactive liquid waste. The volume of the waste sample and its distribution around the detector have a direct impact on the detection efficiency.PurposeThis study aims to explore the variation law of the size parameters of the optimal Marlin cup sample box and provide a basis for subsequent monitoring methods.MethodsThe LaBr3(Ce) crystal was applied to the detection of nuclide activity in medical radioactive waste liquid. Geant4 tool was employed to establish a LaBr3(Ce) crystal detection model. The changing rules of the optimal Marin cup sample box size parameters were explored using a Ø25.4 mm×25.4 mm LaBr3(Ce) detector, and 3D printed photosensitive resin samples were used in the laboratory box for verification experiments.ResultsExperimental results show that simply increasing the sample volume cannot improve the detection efficiency, and the change trend of the detection efficiency in the depth direction of the annular part of the sample container tends to be flat with increase of the sample volume. The optimal size ratio of the Marinelli beaker is that the depth of the annular portion (h2) and the radius (r) are approximately two times the length of the detector crystal and the diameter of the hollow cavity, respectively, and the ratio of the radius (r) to the height of the sample container (H) is approximately 0.5. The experimental results of the full energy peak detection efficiency with optimized sample container size are consistent with the simulation results, and the relative deviation is better than 2.5%.ConclusionsThe results of the study provide an important technical reference for detector selection, sampling container design, and processing and traceability methods of medical radioactive liquid waste monitoring devices.

The study investigated the effect of task complexity (TC) on second language (L2) learners' affective responses and writing performance and how these were modulated by cognitive and affective individual difference (ID) factors. A total of 412 Chinese 8th‐grade English‐as‐a‐foreign‐language learners completed a working memory (WM) test, a scale measuring trait‐like L2 writing enjoyment, a simple (n = 206) or complex (n = 206) argumentative writing task, and posttask scales measuring task‐specific enjoyment and motivation. Independent t‐test results showed that increased TC contributed to a slight but significant enhancement in task motivation and enjoyment and a significant performance improvement in content and organization but not in language. Structural equation modeling results showed that the cognitive and affective ID factors predicted writing performance jointly: WM and task motivation predicted writing performance consistently in both simple and complex tasks, task‐specific enjoyment only played its role in the complex task, and trait‐like enjoyment became insignificant in predicting task performance. These findings support the integrated task‐mediated cognitive–affective model of L2 writing we propose by synthesizing and extending existing models. This study highlights the need to pay attention to the affective dimension of tasks and suggests TC as an intervention strategy to make a task more motivating and enjoyable. [ABSTRACT FROM AUTHOR]

Most research into second language (L2) writing has focused on the products of writing tasks; much less empirical work has examined the behaviours in which L2 writers engage and the cognitive processes that underlie writing behaviours. We aimed to fill this gap by investigating the extent to which writing speed fluency, pausing, eye-gaze behaviours and the cognitive processes associated with pausing may vary across independent and integrated tasks throughout the whole, and at five different stages, of the writing process. Sixty L2 writers performed two independent and two integrated TOEFL iBT writing tasks counterbalanced across participants. While writing, we logged participants' keystrokes and captured their eye-movements. Participants took part in a stimulated recall interview based on the last task they had completed. Mixed effects regressions and qualitative analyses revealed that, apart from source use on the integrated task, L2 writers engaged in similar writing behaviours and cognitive processes during the independent and integrated tasks. The integrated task, however, elicited more dynamic and varied behaviours and cognitive processes across writing stages. Adopting a mixed-methods approach enabled us to gain more complete and specific insights than using a single method.

In this work, we study the asymptotic behavior of the structurally damped wave equations arising from the viscoelastic mechanics. We are particularly interested in the complicated interaction of the time‐dependent oscillating coefficients on the Dirichlet Laplacian operator and the structurally damped terms. On the one hand, by the application of WKB analysis, we explore the asymptotic energy estimates of the wave equations influenced by four types of oscillating mechanisms. On the other hand, in order to prove the optimality of the energy estimates for the critical cases, typical coefficients and initial Cauchy data will be constructed to show the lower bound of the energy growth rate by the application of instability arguments. [ABSTRACT FROM AUTHOR]

In this work, Ru–CeO2 prepared by a "melting" method and used as a heterogeneous catalyst for ethylene methoxy-carbonylation was investigated, together with two other catalysts prepared by impregnation and aerosol methods. The Ru–CeO2 (1%-M) catalyst demonstrates activity significantly higher than that of the other catalysts with the same Ru content. The XPS and Raman analysis results suggest that the Ru–CeO2 (1%-M) oxygen vacancy content is not the highest among the catalysts prepared using the three methods, even though the content oxygen vacancies have been reported to play a crucial role in carbonylation when using a Ru–CeO2 catalyst. It was discovered that the available Ru0 (Ru0 in the freshly prepared sample plus that being transformed from Run+ during reduction) is the other decisive factor in determining the catalyst's performance. We further investigated the high reducibility of the catalyst prepared by using the melting method and discovered that a weak metal–support interaction could be obtained because of the independent formations of Ru and CeO2 crystals with graphite carbon as the barrier. Removing carbon under the optimal conditions could facilitate the as-formed Ru crystals anchored onto CeO2; therefore, there is no strong interaction between Ru and CeO2. [ABSTRACT FROM AUTHOR]