Enhancing surface heat transfer by carbon nanofins: towards an alternative to nanofluids?

Background: Nanofluids are suspensions of nanoparticles and fibers which have recently attracted much attention because of their superior thermal properties. Nevertheless, it was proven that, due to modest dispersion of nanoparticles, such high expectations often remain unmet. In this article, by introducing the notion of nanofin, a possible solution is envisioned, where nanostructures with high aspect-ratio are sparsely attached to a solid surface (to avoid a significant disturbance on the fluid dynamic structures), and act as efficient thermal bridges within the boundary layer. As a result, particles are only needed in a small region of the fluid, while dispersion can be controlled in advance through design and manufacturing processes. Results: Toward the end of implementing the above idea, we focus on single carbon nanotubes to enhance heat transfer between a surface and a fluid in contact with it. First, we investigate the thermal conductivity of the latter nanostructures by means of classical non-equilibrium molecular dynamics simulations. Next, thermal conductance at the interface between a single wall carbon nanotube (nanofin) and water molecules is assessed by means of both steady-state and transient numerical experiments. Conclusions: Numerical evidences suggest a pretty favorable thermal boundary conductance (order of 107 W·m-2·K-1) which makes carbon nanotubes potential candidates for constructing nanofinned surface

Electron-beam-assisted superplastic shaping of nanoscale amorphous silica

At room temperature, glasses are known to be brittle and fracture upon deformation. Zheng et al. show that, by exposing amorphous silica nanostructures to a low-intensity electron beam, it is possible to achieve dramatic shape changes, including a superplastic elongation of 200% for nanowires

Influence of Matrix Polarity on the Properties of Ethylene Vinyl Acetate–Carbon Nanofiller Nanocomposites

A series of ethylene vinyl acetate (EVA) nanocomposites using four kinds of EVA with 40, 50, 60, and 70 wt% vinyl acetate (VA) contents and three different carbon-based nanofillers—expanded graphite (EG), multi-walled carbon nanotube (MWCNT), and carbon nanofiber (CNF) have been prepared via solution blending. The influence of the matrix polarity and the nature of nanofillers on the morphology and properties of EVA nanocomposites have been investigated. It is observed that the sample with lowest vinyl acetate content exhibits highest mechanical properties. However, the enhancement in mechanical properties with the incorporation of various nanofillers is the highest for EVA with high VA content. This trend has been followed in both dynamic mechanical properties and thermal conductivity of the nanocomposites. EVA copolymer undergoes a transition from partial to complete amorphousness between 40 and 50 wt% VA content, and this changes the dispersion of the nanofillers. The high VA-containing polymers show more affinity toward fillers due to the large free volume available and allow easy dispersion of nanofillers in the amorphous rubbery phase, as confirmed from the morphological studies. The thermal stability of the nanocomposites is also influenced by the type of nanofiller

The insulin polymorphism -23Hph increases the risk for type 1 diabetes mellitus in the Romanian population

The insulin -23Hph and IGF2 Apa polymorphisms were genotyped in Romanian patients with T1DM (n = 204), T2DM (n = 215) or obesity (n = 200) and normoponderal healthy subjects (n = 750). The genotypes of both polymorphisms were distributed in concordance with Hardy-Weinberg equilibrium in all groups. The -23Hph AA genotype increased the risk for T1DM (OR: 3.22, 95%CI: 2.09-4.98, p < 0,0001), especially in patients without macroalbuminuria (OR: 4.32, 95%CI: 2.54-7.45, p < 0,0001). No other significant association between the alleles or genotypes of insulin -23Hph and IGF2 Apa and diabetes or obesity was identified

INS VNTR allelic variation and dynamic insulin secretion in healthy adult non-diabetic Caucasian subjects.

AIMS: To elucidate the relationship between the human insulin gene INS VNTR regulatory polymorphism and insulin secretion. The polymorphism arises from tandem repetition of 14-15 bp oligonucleotides. In Caucasians, repeat number varies from 26 to over 200, with two main and discrete allele size classes: class I (26-63 repeats) and class III (141-209 repeats). Class I allele homozygosity is associated with elevated risk of developing Type 1 diabetes, while the class III allele has been associated with increased risk of Type 2 diabetes, polycystic ovary syndrome (PCOS) and with larger size at birth, which may influence development of adult disease. METHODS: Thirty-one healthy adult subjects with normal glucose tolerance, underwent an intravenous glucose tolerance test with one minute sampling. Seventeen subjects were homozygous for class I alleles (14 excluding individuals carrying alleles associated with parent-of-origin effects and heterogeneity in allele transmission) and 14 homozygous for class III alleles. The groups were well matched. RESULTS: No significant differences in amount or rate of insulin secretion, or beta cell function were detected between the two groups. There was a difference in pattern of pulsatile insulin secretion with more 9-minute oscillations in class I homozygotes (P<0.026). The after-load glucose concentration was also higher in subjects with class I alleles (P<0.03). CONCLUSIONS: These results warrant further analysis of possible association between allelic variation of the INS VNTR and the pulsatility of insulin secretion

Effect of substrates and underlayer on CNT synthesis by plasma enhanced CVD

Due to their unique thermal, electronic and mechanical properties, carbon nanotubes (CNTs) have aroused various attentions of many researchers. Among all the techniques to fabricate CNTs, plasma enhanced chemical vapor deposition (PECVD) has been extensively developed as one growth technique to produce vertically-aligned carbon nanotubes (VACNTs). Though CNTs show a trend to be integrated into nanoelectromechanical system (NEMS), CNT growth still remains a mysterious technology. This paper attempts to reveal the effects of substrates and underlayers to CNT synthesis. We tried five different substrates by substituting intrinsic Si with high resistivity ones and by increasing the thickness of SiO2 insulativity layer. And also, we demonstrated an innovative way of adjusting CNT density by changing the thickness of Cu underlayer. \ua9 2013 Shanghai University and Springer-Verlag Berlin Heidelberg