Molecular Dynamics Study of the Catalyst Particle Size Dependence on Carbon Nanotube Growth

The molecular dynamics method, based on an empirical potential energy surface, was used to study the effect of catalyst particle size on the growth mechanism and structure of single-walled carbon nanotubes (SWNTs). The temperature for nanotube nucleation (800-1100 K), which occurs on the surface of the cluster, is similar to that used in catalyst chemical vapor deposition experiments, and the growth mechanism, which is described within the vapor-liquid-solid model, is the same for all cluster sizes studied here (iron clusters containing between 10 and 200 atoms were simulated). Large catalyst particles, that contain at least 20 iron atoms, nucleate SWNTs and have a far better tubular structure than SWNTs nucleated from smaller clusters. In addition, the SWNTs that grow from the larger clusters have diameters that are similar to the cluster diameter, whereas the smaller clusters, which have diameters less than 0.5 nm, nucleate nanotubes that are approximately 0.6-0.7 nm in diameter. This is in agreement with the experimental observations that SWNT diameters are similar to the catalyst particle diameter, and that the narrowest free-standing SWNT is 0.6-0.7 nm

Molecular Dynamics Study of Bamboo-like Carbon Nanotube Nucleation

MD simulations based on an empirical potential energy surface were used to study the nucleation of bamboo-like carbon nanotubes (BCNTs). The simulations reveal that inner walls of the bamboo structure start to nucleate at the junction between the outer nanotube wall and the catalyst particle. In agreement with experimental results, the simulations show that BCNTs nucleate at higher dissolved carbon concentrations (i.e., feedstock pressures) than those where non-bamboolike carbon nanotubes are nucleated

Portfolio Vol. I N 3

Sweitzer, Harry J. Portfolio Goes to Press . Prose. 1. Browne, Phil. William Howard Doane Library . Picture. 2. Overhuls, James. Out of Himself . Prose. 3. MacNeill, Annie Marie. To President and Mrs. Shaw . Poem. 6. Baker, George. Saint in a Silo . Prose 7. Beckham, Adela. In Moods . Poem. 8. Vincent, Charles. Incident of August 7, 1930. Prose. 9. Flory, Doris. Opinions . Poem. 10. Flory, Doris. Thoughts in Spring . Poem. 10. Flory, Doris. Breakfast Scene . Poem. 10. Shaw, Robert B. A Date for the Dances . Prose. 11. Cronberger, Barbara. And the Years Go On . Prose. 13. Hanna, Stanley. Reola, Reola . Poem. 14. Hanna, Stanley. The Dance of the Kobolds . Poem. 14. Nadel, Norman. I died Last Night . Prose. 15. Bethune, Don S. Adolescence . Poem 16. Vodev, Eugene. The Black Day of Bulgaria . Prose. 17. Dick, Pewilla. To a White Violet . Poem. 18. Dick, Pewilla. As With Your Shadow . Poem. 18. Dwelly, Thorndike. Of Mice and Men . Prose. 19. Clements, Helen. Our Town . Prose. 19. Schlle, Alice. Marion is an Old Costume . Picture. 20. Chadeayne, Robert. Factory . Picture. 20. Nadel, Norman. Dmitri Shostakovitch . Prose. 21. Stewart, John. Duke Ellington\u27s Records . Prose. 21. Beck, Virginia. The Dance as an Art . Prose. 22. Dick, Pewilla. Death . Poem. 23. Flory, Doris. On Reforms . Poem. 24. Beckham, Adela. The Lie . Poem. 24. Bethune, Don. Futility . Poem. 24

Antenatal magnetic resonance imaging versus ultrasound for predicting neonatal macrosomia: a systematic review and meta-analysis

BACKGROUND: Fetal macrosomia is associated with an increased risk of adverse maternal and neonatal outcomes. OBJECTIVES: To compare the accuracy of antenatal two-dimensional (2D) ultrasound, three-dimensional (3D) ultrasound, and magnetic resonance imaging (MRI) in predicting fetal macrosomia at birth. SEARCH STRATEGY: Medline (1966-2013), Embase, the Cochrane Library and Web of Knowledge. SELECTION CRITERIA: Cohort or diagnostic accuracy studies of women with a singleton pregnancy, who had third-trimester imaging to predict macrosomia (>4000 g, >4500 g or >90th or >95th centile). DATA COLLECTION AND ANALYSIS: Two reviewers screened studies, performed data extraction and assessed methodological quality. The bivariate model was used to obtain summary sensitivities, specificities and likelihood ratios. MAIN RESULTS: Fifty-eight studies (34 367 pregnant women) were included. Most were poorly reported. Only one study assessed 3D ultrasound volumetry. For predicting birthweight >4000 g or >90th centile, the summary sensitivity for 2D ultrasound (Hadlock) estimated fetal weight (EFW) >90th centile or >4000 g (29 studies) was 0.56 (95% CI 0.49-0.61), 2D ultrasound abdominal circumference (AC) >35 cm (four studies) was 0.80 (95% confidence interval [95% CI] 0.69-0.87) and MRI EFW (three studies) was 0.93 (95% CI 0.76-0.98). The summary specificities were 0.92 (95% CI 0.90-0.94), 0.86 (95% CI 0.74-0.93) and 0.95 (95% CI 0.92-0.97), respectively. CONCLUSION: There is insufficient evidence to conclude that MRI EFW is more sensitive than 2D ultrasound AC (which is more sensitive than 2D EFW); although it was more specific. Further primary research is required before recommending MRI EFW for use in clinical practice

Synthesis of carbon nanotubes with and without catalyst particles

The initial development of carbon nanotube synthesis revolved heavily around the use of 3d valence transition metals such as Fe, Ni, and Co. More recently, noble metals (e.g. Au) and poor metals (e.g. In, Pb) have been shown to also yield carbon nanotubes. In addition, various ceramics and semiconductors can serve as catalytic particles suitable for tube formation and in some cases hybrid metal/metal oxide systems are possible. All-carbon systems for carbon nanotube growth without any catalytic particles have also been demonstrated. These different growth systems are briefly examined in this article and serve to highlight the breadth of avenues available for carbon nanotube synthesis

Effect of Temperature Gradient Direction in the Catalyst Nanoparticle on CNTs Growth Mode

To improve the understanding on CNT growth modes, the various processes, including thermal CVD, MP-CVD and ECR-CVD, have been used to deposit CNTs on nanoporous SBA-15 and Si wafer substrates with C2H2 and H2 as reaction gases. The experiments to vary process parameter of ΔT, defined as the vector quantities of temperature at catalyst top minus it at catalyst bottom, were carried out to demonstrate its effect on the CNT growth mode. The TEM and TGA analyses were used to characterize their growth modes and carbon yields of the processes. The results show that ΔT can be used to monitor the temperature gradient direction across the catalyst nanoparticle during the growth stage of CNTs. The results also indicate that the tip-growth CNTs, base-growth CNTs and onion-like carbon are generally fabricated under conditions of ΔT > 0, <0 and ~0, respectively. Our proposed growth mechanisms can be successfully adopted to explain why the base- and tip-growth CNTs are common in thermal CVD and plasma-enhanced CVD processes, respectively. Furthermore, our experiments have also successfully demonstrated the possibility to vary ΔT to obtain the desired growth mode of CNTs by thermal or plasma-enhanced CVD systems for different applications

Social and professional influences on antimicrobial prescribing for doctors-in-training: a realist review.

Background: Antimicrobial resistance has led to widespread implementation of interventions for appropriate prescribing. However, such interventions are often adopted without an adequate understanding of the challenges facing doctors-in-training as key prescribers. Methods: The review followed a realist, theory-driven approach to synthesizing qualitative, quantitative and mixed-methods literature. Consistent with realist review quality standards, articles retrieved from electronic databases were systematically screened and analysed to elicit explanations of antimicrobial prescribing behaviours. These explanations were consolidated into a programme theory drawing on social science and learning theory, and shaped though input from patients and practitioners. Results: By synthesizing data from 131 articles, the review highlights the complex social and professional dynamics underlying antimicrobial prescribing decisions of doctors-in-training. The analysis shows how doctors-in-training often operate within challenging contexts (hierarchical relationships, powerful prescribing norms, unclear roles and responsibilities, implicit expectations about knowledge levels, uncertainty about application of knowledge in practice) where they prioritize particular responses (fear of criticism and individual responsibility, managing one's reputation and position in the team, appearing competent). These complex dynamics explain how and why doctors-in-training decide to: (i) follow senior clinicians' prescribing habits; (ii) take (or not) into account prescribing aids, advice from other health professionals or patient expectations; and (iii) ask questions or challenge decisions. This increased understanding allows for targeted tailoring, design and implementation of antimicrobial prescribing interventions. Conclusions: This review contributes to a better understanding of how antimicrobial prescribing interventions for doctors-in-training can be embedded more successfully in the hierarchical and inter-professional dynamics of different healthcare settings