Flow cytometry-based evaluation and enrichment of multiwalled carbon nanotube dispersions

The uniform aqueous dispersion of carbon nanotubes (CNTs) is a vital but challenging task required for their utilization in most technologies. We propose and demonstrate a technique based on forward- and side-scatter analysis on a flow cytometer to characterize the components in a dispersion of multiwalled CNTs (MWCNTs). The method simultaneously distinguishes various MWCNT components such as short and long CNTs, nanotube bundles, and particulates. It also detects the emergence of new CNT populations as a result of centrifugation. We use this method, together with classical methods such as UV and Raman spectroscopy, to observe and study the multistep MWCNT dispersion process in various surfactants (Pluronic, Triton X-100, sodium dodecyl sulfate, and cetyl trimethylammonium bromide). On the basis of the distinct scatter patterns obtained, we confirm and elaborate the surfactant-assisted unzipping mechanism of MWCNT dispersion. We also show that the ultrasonic energy spent after MWCNT unbundling and unwinding can be minimized and the process optimized for each surfactant by correct end point detection through scatter analysis. The ability to enrich nanotube population in dispersion by using the sorting mode of a flow cytometer is confirmed by electron microscopy and Raman spectroscopy. This method can thus be used for observing and enriching MWCNT components and as a complementary technique to UV spectroscopy for studying and optimizing MWCNT dispersion in surfactants.     

Importance of Tollmien's Counter Example

Efforts to construct a general theoretical basis containing the essential features of Tollmien's counter example to the sufficiency of Rayleigh's theorem on point of inflexion have resulted in the determination of a pair of upper bounds of the rate of growth of arbitrary unstable disturbances; whereas, the necessary condition of the existence of these upper bounds have provided access to a sufficient condition of stability in its simplest form in the equilibrium of homogeneous incompressible inviscid parallel shear flows that are not known as yet and go beyond the works of Rayleigh [1], Tollmien [2], Friedrichs [3], Fjortoft [4], Hoiland [5], Howard [6, 7], Hickernell [8], and Banerjee et al. [9]. An alternative proof of the result that a wide class of such flows could be made stable by bringing the boundaries sufficiently close, although the flow has a point of inflexion inside the domain of flow with the Fjortoft's criterion satisfied, which is derived by Drazin and Howard [10] from variational formulation of the problem follows as an outcome of the expressions of these upper bounds. The counter example has played the role of a forerunner for much of the development that followed in its wake after 1935, and the present succession of papers is especially undertaken to investigate the trail left behind by the counter example and, it is hoped, to arrive at a necessary and sufficient condition of stability in its simplest form, which is still missing in the literature on the subject.     

Production of Hydrogen by Glycerol Photoreforming Using Binary Nitrogen–Metal‐Promoted N‐M‐TiO2 Photocatalysts

The need for renewable energy focuses attention on hydrogen obtained by using sustainable and green methods. The sustainable compound glycerol can be used for hydrogen production by heterogeneous photocatalysis. A novel approach involves the promotion of the TiO₂ photocatalyst with a binary combination of nitrogen and transition metal. We report the synthesis and spectroscopic characterization of the new N‐M‐TiO₂ photocatalysts (M=none, Cr, Co, Ni, Cu), and the photocatalytic reforming of glycerol to hydrogen under ambient conditions and near‐UV or visible light versus benchmark P25 TiO₂. In units of activity μmol m^?2 h^?1, N‐Ni‐TiO₂ is five‐fold more active than P25, and N‐Cu‐TiO₂ is 44‐fold more active. The photocatalytic activity of N‐M‐TiO₂ increases from Cr to Co and Ni, whereas the photoluminescence decreases; the change in activity is due to the modulation of charge recombination.     

On reducing Howard's semicircle for homogeneous shear flows

Howard's semicircle bound on the range of the complex wave velocity of an arbitrary unstable mode in the stability problem of homogeneous shear flows is further reduced. The reduction depends on the curvature of the velocity profile and the depth of the fluid layer.     

A Spatially Non-Local Model for Flow in Porous Media

A general mathematical model of steady-state transport driven by spatially non-local driving potential differences is proposed. The porous medium is considered to be a network of short-, medium-, and long-range interstitial channels with impermeable walls and at a continuum of length scales, and the flow rate in each channel is assumed to be linear with respect to the pressure difference between its ends. The flow rate in the model is thus a functional of the non-local driving pressure differences. As special cases, the model reduces to familiar forms of transport equations that are commonly used. An important situation arises when the phenomenon is almost, but not quite, locally dependent. The one-dimensional form of the model discussed here can be extended to multiple dimensions, temporal non-locality, and to heat, mass, and momentum transfer.     

Comparative and Combinatorial Effects of Resveratrol and Sacubitril/Valsartan alongside Valsartan on Cardiac Remodeling and Dysfunction in MI-Induced Rats

The development and progression of heart failure (HF) due to myocardial infarction (MI) is a major concern even with current optimal therapy. Resveratrol is a plant polyphenol with cardioprotective properties. Sacubitril/valsartan is known to be beneficial in chronic HF patients. In this study, we investigated the comparative and combinatorial benefits of resveratrol with sacubitril/valsartan alongside an active comparator valsartan in MI-induced male Sprague Dawley rats. MI-induced and sham-operated animals received vehicle, resveratrol, sacubitril/valsartan, valsartan alone or sacubitril/valsartan + resveratrol for 8 weeks. Echocardiography was performed at the endpoint to assess cardiac structure and function. Cardiac oxidative stress, inflammation, fibrosis, brain natriuretic peptide (BNP), creatinine and neutrophil gelatinase associated lipocalin were measured. Treatment with resveratrol, sacubitril/valsartan, valsartan and sacubitril/valsartan + resveratrol significantly prevented left ventricular (LV) dilatation and improved LV ejection fraction in MI-induced rats. All treatments also significantly reduced myocardial tissue oxidative stress, inflammation and fibrosis, as well as BNP. Treatment with the combination of sacubitril/valsartan and resveratrol did not show additive effects. In conclusion, resveratrol, sacubitril/valsartan, and valsartan significantly prevented cardiac remodeling and dysfunction in MI-induced rats. The reduction in cardiac remodeling and dysfunction in MI-induced rats was mediated by a reduction in cardiac oxidative stress, inflammation and fibrosis.     

Hue‐ and Chromaticity‐Based Exploration of Surface Complexation‐Induced Tunable Emission from Non‐Luminescent Quantum Dots

Herein we report the use of a hue parameter of HSV (Hue, Saturation and Value) color space—in combination with chromaticity color coordinates—for exploring the complexation‐induced luminescence color changes, ranging from blue to green to yellow to white, from a non‐luminescent Fe‐doped ZnS quantum dot (QD). Importantly, the surface complexation reaction helped a presynthesized non‐luminescent Fe‐doped ZnS QD to glow with different luminescence colors (such as blue, cyan, green, greenish‐yellow, yellow) by virtue of the formation of various luminescent inorganic complexes (using different external organic ligands), while the simultaneous blue‐ and yellow‐emitting complex formation on the surface of non‐luminescent Fe‐doped ZnS QD led to the generation of white light emission, with a hue mean value of 85 and a chromaticity of (0.28,0.33). Furthermore, the surface complexation‐assisted incorporation of luminescence properties to a non‐luminescent QD not only overcomes their restricted luminescence‐based applications such as light‐emitting, biological and sensing applications but also bring newer avenues towards unravelling the surface chemistry between QDs and inorganic complexes and the advantage of having an inorganic complex with QD for their aforementioned useful applications.     

A study of the effect of JB particles on Saccharomyces cerevisiae (yeast) cells by Raman spectroscopy

The mechanism of interaction of particulate matter with living system is not completely understood. Evaluation of the effect of particulate Indian traditional medicine JB(JB) on Saccharomyces cerevisiae (yeast) cells is the major focus of the present study. In India, JB is considered as a rejuvenating medicine and used for the treatment of diseases such as diabetes and age‐related eye diseases, as well as a health promoting tonic by the traditional practitioners. In presence of JB, higher growth has been observed at the late stationary growth phase of yeast. Ultra‐structure analysis using transmission electron microscopy (TEM) has shown that JB‐treated yeast cells have better morphology over control in the late stationary growth phase. In this investigation, cellular response from yeast cells after interaction with JB particles was measured using Raman spectroscopy. Raman spectroscopy—a noninvasive tool to distinguish between particle‐treated and untreated cells—revealed that treatment with JB is able to slow the degradation of cellular components (e.g. DNA, proteins and lipids) with the aging of yeast cells. Copyright © 2008 John Wiley & Sons, Ltd.     

An equivalence in hydromagnetics

In an infinitely extended hydromagnetic system with a unidirectional magnetic field, the following correspondence exists: for every magnetohydrostatic problem of finite conductivity there is a compressible magnetohydrodynamic problem of infinite conductivity.