Telomers ionically tethered to nanometer-sized particles yield self-suspended, nanoparticle-laden liquids with unusual dynamical features. By subjecting these suspensions to controlled, modest shear strains, we find that their flow behaviors observed using experiments performed on time scales of tens of seconds can be projected to obtain maps of their dynamical response on geological time scales. That such extraordinarily slow dynamic processes can be uncovered from real-time measurements by simply stretching a system provides a simple but powerful tool for interrogating extremely slow motions in other jammed physical states.
Figure 1. CUL4B deficiency in pancreatic δ cells impairs glucose metabolism. (A and B)Western blots and quantitative data for CUL4A and CUL4B protein levels in islets from 12-week-old diabetic db/db mice and their heterozygous littermates (db/+). n = 6 mice per group. Representative Western blots from at least 3 independent experiments are shown. (C) Immunostaining for CUL4B (green) and somatostatin (SST, red) in pancreatic sections from db/db and db/+ mice. Scale bar: 100 μm. n = 6 mice per group; 4-7 random areas were selected from each islet section, and 10 sections were randomly selected from each mouse. Insulininduced decreases in blood glucose levels were significantly lower in Sst-Cre +/-Cul4b fl/Y mice than in their WT littermates, and they did not return to baseline levels at the 2-hour time point, whereas the levels of their WT littermates did (n = 9-11). *P < 0.05; **P < 0.01; ***P < 0.001. db/db mice were compared with their db/+ littermates, and Sst-Cre +/-Cul4b fl/Y mice were compared with their WT littermates. Error bars in F represent mean ± SD; other bars represent mean ± SEM. All data were analyzed using 1-way ANOVA. The Journal of Clinical Investigation R E S E A R C H A R T I C L E2 6 3 3 jci.orgVolume 127 Number 7 July 2017mental Figure 1E). Immunofluorescence also showed no significant differences in islet or β or δ cell numbers between +/-mice, the knockout mice exhibited increased glucose levels after 2 hours of feeding following a 16-hour fast ( Figure 1G). Accordingly, during a glucose tolerance test, the blood glucose levels of Sst-Cre +/-Cul4b fl/Y mice were 33% and 30% higher at 30 minutes and 120 minutes, respectively, than those of the control group consisting of both Sst-Cre +/-and Cul4b fl/Y mice ( Figure 1H). In addition, during the insulin tolerance test, the blood glucose levels of Sst-Cre +/-Cul4b fl/Y mice unexpectedly decreased more dramatically and rapidly than those of the Sst-Cre +/-control mice in response to insulin stimulation ( Figure 1I). Insulin and somatostatin content as well as kidney, brain, heart, liver, and stomach weights were not found to be significantly different between the mice was 140% and 40% higher than that of Sst-Cre +/-mice at 5 minutes and 60 minutes, respectively ( Figure 2H). In contrast to the results found for the Sst-Cre +/-Cul4b fl/Y mice, CUL4B defistrated that CRL4 ubiquitinates WD repeat-containing protein 5 (WDR5), a core subunit of H3K4 methyltransferase complexes, for degradation in the nucleus, thereby promoting increased H3K4 methylation levels (30). However, whether CUL4B or its E3 ligase complex CRL4B-PRC2 participates in the functioning or development of Langerhans islets has not been studied. In this study, we found that CUL4B expression levels are decreased in db/db mice. Therefore, we crossed mice expressing Cre under the insulin II promotor (Ins2-Cre) and mice expressing Cre under the somatostatin promoter (Sst-Cre) with Cul4b fl/fl mice to characterize CUL4B functions in specific cell types of the islet circuit. Although In...
Silver nanoparticles (Ag NPs) modified with sodium 2-mercaptoethanesulfonate (mesna) exhibit strong surface-enhanced Raman scattering (SERS). Their specific and strong interaction with heavy metal ions led to a labelfree assay for Hg(II). The covalent bond formed between mercury and sulfur is stronger than the one between silver and sulfur and thus prevents the adsorption of mesna on the surface of Ag NPs. This results in a decrease of the intensity of SERS in the presence of Hg(II) ions. The Raman peak at 795 cm −1 can be used for quantification. The effect of the concentration of mesna, the concentration of sodium chloride, incubation time and pH value on SERS were optimized. Under the optimal conditions, the intensity of SERS decreases with increasing concentration of Hg(II). The decrease is linear in the 0.01 and 2 μmol L −1 concentration range, with a correlation coefficient (R 2 ) of 0.996 and detection limit (S/N03) is 0.0024 μmol L −1 . The method was successfully applied to the determination of the Hg(II) in spiked water samples.
Au/Ag core/shell bipyramids were used as surface-enhanced Raman scattering (SERS) substrates to determine the thiram. The metallic substrates showed high SERS performance and are very suitable for the analytical sensors. The fabrication and characterization of the Au/Ag core/shell bipyramids were described. The influence of experimental parameters, such as the thickness of Ag shell of the bipyramids, sodium chloride concentration, and pH value on SERS of thiram was examined and optimized. Under the optimum conditions, thiram molecules were effectively adsorbed onto bipyramids and the SERS intensity is proportional to the concentration of thiram in the range of 3.3 to 400.0 ng mL -1 . The corresponding correlation coefficient of the linear equation is 0.997, which indicates that there is a good linear relationship between SERS intensity and thiram concentration. The limit of detection for thiram is 2.0 ng mL -1 . The experimental results indicate that the proposed method is a viable method for determination of thiram. Some environmental water samples were analyzed and the analytical results were satisfactory.
Time-dependent shear stress versus shear rate, constitutive curve, and velocity profile measurements are reported in entangled polymer solutions during start-up of steady shear flow. By combining confocal microscopy and particle image velocimetry (PIV), we determine the time-dependent velocity profile in polybutadiene and polystyrene solutions seeded with fluorescent 150 nm silica and 7.5 μm melamine particles. By comparing these profiles with time-dependent constitutive curves obtained from experiment and theory, we explore the connection between transient nonmonotonic regions in the constitutive curve for an entangled polymer and its susceptibility to unstable flow by shear banding [Adams et al. Phys. Rev. Lett. 2009, 102, 067801-4]. Surprisingly, we find that even polymer systems which exhibit transient, nonmonotonic shear stress-shear rate relationships in bulk rheology experiments manifest time-dependent velocity profiles that are decidedly linear and show no evidence of unstable flow. We also report that interfacial slip plays an important role in the steady shear flow behavior of entangled polymers at shear rates above the reciprocal terminal relaxation time but has little, if any, effect on the shape of the velocity profile.
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