Experimental investigation of the influence of residual stress due to curing shrinkage on the interphase formation in adhesively bonded joints

AbstractResidual stresses in adhesively bonded joints due to shrinkage (chemical reaction) or thermal movement of the adherents are likely to reduce load capacity of an assembly. In this paper rheometric measurements are used to evaluate the change of viscoelastic properties of the adhesive while curing as well as to determine the perpendicular forces developing in the adhesive joint during the curing process. The results give an indication of potential disturbances in the adhesives polymer network due to residual stresses and relaxation in the transition from the liquid to the solid state

Tasmanian Aborigines and DNA

The hyper-variable control region (HVI and HVII) of mitochondrial DNA (mtDNA) from Tasmanians with an unbroken, direct Tasmanian Aboriginal maternal lineage were DNA sequenced. The lineage dates back to the early 1800s, as evidenced by published family genealogies (Mollison 1978, Ryan 1981, Plomley 1966, 1971, 1987, 1990). Of the five distinct mtDNA haplotypes discovered, VI was found in living Tasmanian descendants traced back to a Port Phillip Aboriginal woman who lived with European sealers in Bass Strait. Haplotype T2 is two nucleotide transitions removed from 1/WD 2 of van Holst Pellekaan et al. 1998 and therefore related to this Australian mainland Aboriginal mtDNA haplotype. Vestiges of Tasmanian maternal mtDNA haplotypes from before white settlement, passing down through up to eight generations, still survive in Tasmania. The Tasmanian Aboriginal people are related and relatable to mainland Aboriginal people

Efficient oxidative dearomatisations of substituted phenols using hypervalent iodine (iii) reagents and antiprotozoal evaluation of the resulting cyclohexadienones against T. b. rhodesiense and P. falciparum Strain NF54

Quinones and quinols are secondary metabolites of higher plants that are associated with many biological activities. The oxidative dearomatization of phenols induced by hypervalent iodine(III) reagents has proven to be a very useful synthetic approach for the preparation of these compounds, which are also widely used in organic synthesis and medicinal chemistry. Starting from several substituted phenols and naphthols, a series of cyclohexadienone and naphthoquinone derivatives were synthesized using different hypervalent iodine(III) reagents and evaluated for their in vitro antiprotozoal activity. Antiprotozoal activity was assessed against Plasmodium falciparum NF54 and Trypanosoma brucei rhodesiense STIB900. Cytotoxicity of all compounds towards L6 cells was evaluated and the respective selectivity indices (SI) were calculated. We found that benzyl naphthoquinone 5c was the most active and selective molecule against T. brucei rhodesiense (IC50 = 0.08 muM, SI = 275). Furthermore, the antiprotozoal assays revealed no specific effects. In addition, some key physicochemical parameters of the synthesised compounds were calculated

Palladium-catalysed synthesis of arylnaphthoquinones as antiprotozoal and antimycobacterial agents

Malaria and tuberculosis are still among the leading causes of death in low-income countries. The 1,4-naphthoquinone (NQ) scaffold can be found in a variety of anti-infective agents. Herein, we report an optimised, high yield process for the preparation of various 2-arylnaphthoquinones by a palladium-catalysed Suzuki reaction. All synthesised compounds were evaluated for their in-vitro antiprotozoal and antimycobacterial activity. Antiprotozoal activity was assessed against Plasmodium falciparum (P.f.) NF54 and Trypanosoma brucei rhodesiense (T.b.r.) STIB900, and antimycobacterial activity against Mycobacterium smegmatis (M.s.) mc(2) 155. Substitution with pyridine and pyrimidine rings significantly increased antiplasmodial potency of our compounds. The 2-aryl-NQs exhibited trypanocidal activity in the nM range with a very favourable selectivity profile. (Pseudo)halogenated aryl-NQs were found to have a pronounced effect indicating inhibition of mycobacterial efflux pumps. Cytotoxicity of all compounds towards L6 cells was evaluated and the respective selectivity indices (SI) were calculated. In addition, the physicochemical parameters of the synthesised compounds were discussed

Ring current effects: Factors affecting the NMR chemical shift of molecules adsorbed on porous carbons

Nuclear magnetic resonance (NMR) spectroscopy is increasingly being used to study the adsorption of molecules in porous carbons, a process which underpins applications ranging from electrochemical energy storage to water purification. Here we present density functional theory (DFT) calculations of the nucleus-independent chemical shift (NICS) near various sp2-hybridized carbon fragments to explore the structural factors that may affect the resonance frequencies observed for adsorbed species. The domain size of the delocalized electron system affects the calculated NICSs, with larger domains giving rise to larger chemical shieldings. In slit pores, overlap of the ring current effects from the pore walls is shown to increase the chemical shielding. Finally, curvature in the carbon sheets is shown to have a significant effect on the NICS. The trends observed are consistent with existing NMR results as well as new spectra presented for an electrolyte adsorbed on carbide-derived carbons prepared at different temperatures

Fabrication of bismuth nanowires with a silver nanocrystal shadowmask

We fabricated bismuth (Bi) nanowires with low energy electron beam lithography using silver (Ag) nanocrystal shadowmasks and a subsequent chlorine reactive ion etching. Submicron-size metal contacts on the single Bi nanowire were successfully prepared by in situ focused ion beam metal deposition for transport measurements. The temperature dependent resistance measurements on the 50 nm wide Bi nanowires showed that the resistance increased with decreasing temperature, which is characteristic of semiconductors and insulators

Anisometric Charge Dependent Swelling of Porous Carbon in an Ionic Liquid

In situ electrochemical dilatometry was used to study, for the first time, the expansion behavior of a porous carbon electrode in a pure ionic liquid, 1-ethyl-3-methyl-imidazolium-tetrafluoroborate. For a single electrode, an applied potential of -2 V and +2 V against the potential of zero charge resulted in maximum strain of 1.8 % and 0.5 %, respectively. During cyclic voltammetry, the characteristic expansion behavior strongly depends on the scan rate, with increased scan rates leading to a decrease of the expansion. Chronoamperometry was used to determine the equilibrium specific capacitance and expansion. The obtained strain versus accumulated charge relationship can be fitted with a simple quadratic function. Cathodic and anodic expansion data collapses on one parabola when normalizing the surface charge by the ratio of ion volume and average pore size. There is also a transient spike in the height change when polarity is switched from positive to negative that is not observed when changing the potential from negative to positive indicating the size and the shape of the ion is influencing the expansion behavior.Comment: 10 pages double spaced, 3 figs, Electrochemistry Communications, accepte

Reversibly compressible and freestanding monolithic carbon spherogels

We present a versatile strategy to tailor the nanostructure of monolithic carbon aerogels. By use of an aqueous colloidal solution of polystyrene in the sol-gel processing of resorcinol-formaldehyde gels, we can prepare, after supercritical drying and successive carbonization, freestanding monolithic carbon aerogels, solely composed of interconnected and uniformly sized hollow spheres, which we name carbon spherogels. Each sphere is enclosed by a microporous carbon wall whose thickness can be adjusted by the polystyrene concentration, which affects the pore texture as well as the mechanical properties of the aerogel monolith. In this study, we used monodisperse polystyrene spheres of approximately 250 nm diameter, which result in an inner diameter of the final hollow carbon spheres of approximately 200 ± 5 nm due to shrinkage during the carbonization process. The excellent homogeneity of the samples, as well as uniform sphere geometries, are confirmed by small- and angle X-ray scattering. The presence of macropores between the hollow spheres creates a monolithic network with the benefit of being reversibly compressible up to 10% linear strain without destruction. Electrochemical tests demonstrate the applicability of ground and CO2 activated carbon spherogels as electrode materials. © 2019 The Author

The evolutionary dynamics of the Saccharomyces cerevisiae protein interaction network after duplication

Gene duplication is an important mechanism in the evolution of protein interaction networks. Duplications are followed by the gain and loss of interactions, rewiring the network at some unknown rate. Because rewiring is likely to change the distribution of network motifs within the duplicated interaction set, it should be possible to study network rewiring by tracking the evolution of these motifs. We have developed a mathematical framework that, together with duplication data from comparative genomic and proteomic studies, allows us to infer the connectivity of the preduplication network and the changes in connectivity over time. We focused on the whole-genome duplication (WGD) event in Saccharomyces cerevisiae. The model allowed us to predict the frequency of intergene interaction before WGD and the post duplication probabilities of interaction gain and loss. We find that the predicted frequency of self-interactions in the preduplication network is significantly higher than that observed in today's network. This could suggest a structural difference between the modern and ancestral networks, preferential addition or retention of interactions between ohnologs, or selective pressure to preserve duplicates of self-interacting proteins