Synthesis and RNase A inhibition study of C2-symmetric bis-isochromenyl sulfones

A new class of C₂-symmetric bis-isochromene derivatives with 3,3′-linkage has been synthesized from bis-propargyl sulfones. The method involves treatment of the sulfones with triethylamine to form the isochromene derivatives presumably via the intramolecular Michael addition to the intermediate bis-allenic sulfones. Interestingly, the product expected from the Garratt-Braverman pathway was not obtained. The bis-isochromene 7d displayed RNase A inhibition activity, much stronger than the isochromene 8 and bis-isocoumarin 9.     

Contact angle hysteresis of microbead suspensions

Microbead suspensions are often used in microfluidic devices for transporting biomolecules. An experimental investigation on the wettability of microbead suspension is presented in this study. The variation in the surface tension and the equilibrium contact angle with the change in the volume fraction of the microbead is presented here. The surface tension of the microbead suspension is measured with the pendant drop technique, whereas the dynamic contact angle measurements, i.e., advancing and receding contact angles, are measured with the sessile drop technique. An equilibrium contact angle of a suspension with particular volume fraction is determined by computing an average over the measured advancing and receding contact angles. It is observed that the surface tension and the equilibrium contact angle determined from advancing and receding contact angles vary with the magnitude of the microbeads volume fraction in the suspension. A decrease in the surface tension with an increase in the volume fraction of the microbead suspension is observed. The advancement and the recession in contact line for dynamic contact angle measurements are achieved with the motorized dosing mechanism. For microbead suspensions, the advancement of the contact line is faster as compared to the recession of the contact line for the same flow rate. The presence of microbeads assists in the advancement and the recession of the contact line of the suspension. A decrease in the equilibrium contact angles with an increase in the microbead suspension volume fraction is observed. Inclusion of microbeads in the suspension increases the wetting capability for the considered combination of the microbead suspension and substrate. Finally, empirical correlations for the surface tension and the contact angle of the suspension as a function of microbead volume fraction are proposed. Such correlations can readily be used to develop mechanistic models for the capillary transport of microbead suspensions related to LOC applications.     

A Stochastic Perturbation of Inviscid Flows

We prove existence and regularity of the stochastic flows used in the stochastic Lagrangian formulation of the incompressible Navier-Stokes equations (with periodic boundary conditions), and consequently obtain a C ^k,α local existence result for the Navier-Stokes equations. Our estimates are independent of viscosity, allowing us to consider the inviscid limit. We show that as ν → 0, solutions of the stochastic Lagrangian formulation (with periodic boundary conditions) converge to solutions of the Euler equations at the rate of .     

Surface characterisation of ethylene-propylene-diene rubber upon exposure to aqueous acidic solution

Two types of pure ethylene propylene diene rubbers were exposed to two different acids for varying period of time. Surface characterisation was carried out using X-ray photoelectron spectroscopy (XPS). Two EPDM rubbers selected for this study were comparable in co-monomer compositions but significantly different with respect to molar mass and the presence of long chain branching. Both rubbers contained 5-ethylidene-2-norbornene (ENB) as diene. Solution cast films of pure EPDM samples were exposed in two different acidic solutions, viz. chromosulphuric (Cr (VI)/H₂SO₄) and sulphuric acid (H₂SO₄) (20%, v/v) at ambient temperature from 1 to 12 weeks. XPS analysis indicated that several oxygenated species were formed on the surface of both rubbers after exposure. It was postulated from the XPS analyses that both aqueous acidic solutions attacked the olefinic double bonds (CC) of ENB. Furthermore, 20% Cr (VI)/H₂SO₄ also attacked the allylic carbon-hydrogen (CH) bonds of ENB resulting in more oxygenated species on the surface compared to 20% H₂SO₄ under identical conditions. Cr (VI) in the 20% Cr (VI)/H₂SO₄ was found to play an important role in alteration of surface chemistry. Studies using a model system consisting of EPDM mixed with Cr (VI) and Cr (III) salts revealed that the change of oxidation state from Cr (VI) to Cr (III) as a consequence of direct involvement of Cr (VI) in the chemical alteration of EPDM surfaces. Interestingly, the presence of long chain branching and molar mass did not significantly influence the chemical processes owing to the acid treatment.     

Cluster Algebras and Grassmannians of Type <Emphasis Type="Italic">G</Emphasis><Subscript>2</Subscript>

We prove a conjecture of Geiss, Leclerc and Schröer, producing cluster algebra structures on multi-homogeneous coordinate ring of partial flag varieties, for the case G ₂. As a consequence we sharpen the known fact that coordinate ring of the double Bruhat cell \(G^{e,w_0}\) is an upper cluster algebra, by proving that it is a cluster algebra.     

ZnO and ZnS Nanostructures: Ultraviolet-Light Emitters,Lasers, and Sensors

ZnO and ZnS, well-known direct bandgap II–VI semiconductors, are promising materials for photonic, optical, and electronic devices. Nanostructured materials have lent a leading edge to the next generation technology due to their distinguished performance and efficiency for device fabrication. As two of the most suitable materials with size- and dimensionality-dependent functional properties, wide bandgap semiconducting ZnO and ZnS nanostructures have attracted particular attention in recent years. For example, both materials have been assembled into nanometer-scale visible-light-blind ultraviolet (UV) light sensors with high sensitivity and selectivity, in addition to other applications such as field emitters and lasers. Their high-performance characteristics are particularly due to the high surface-to-volume ratios (SVR) and rationally designed surfaces. This article provides a comprehensive review of the state-of-the-art research activities in ZnO and ZnS nanostructures, including their syntheses and potential applications, with an emphasis on one-dimensional (1D) ZnO and ZnS nanostructure-based UV light emissions, lasers, and sensors. We begin with a survey of nanostructures, fundamental properties of ZnO and ZnS, and UV radiation–based applications. This is followed by detailed discussions on the recent progress of their synthesis, UV light emissions, lasers, and sensors. Additionally, developments of ZnS/ZnO composite nanostructures, including core/shell and heterostructures, are discussed and their novel optical properties are reviewed. Finally, we conclude this review with the perspectives and outlook on the future developments in this area. This review explores the possible influences of research breakthroughs of ZnO and ZnS nanostructures on the current and future applications for UV light–based lasers and sensors.     

Wing-type vortex generators for fin-and-tube heat exchangers

The effect of wing-type vortex generators on heat transfer and pressure drop of a fin-and-tube heat exchanger element was investigated. Local heat transfer was measured by liquid crystal thermography on the fin in the Reynolds number range of 600–2700. Flow losses were estimated from the measured pressure drop of an element. Delta winglets were used as vortex generators. Four fin-and-tube configurations were tested, an inline and a staggered arrangement, each with plain fins and with fins with a pair of vortex generators behind each tube. For the inline tube arrangement the vortex generators increase the heat transfer by 55–65% with a corresponding increase of 20–45% in the apparent friction factor. Results indicate that the vortex generators have the potential to reduce considerably the size and mass of heat exchangers for a given heat load.     

Assouad-Nagata dimension via Lipschitz extensions

In the first part of the paper we show how to relate several dimension theories (asymptotic dimension with Higson property, asymptotic dimension of Gromov and capacity dimension of Buyalo [7]) to Assouad-Nagata dimension. This is done by applying two functors on the Lipschitz category of metric spaces: microscopic and macroscopic. In the second part we identify (among spaces of finite Assouad-Nagata dimension) spaces of Assouad-Nagata dimension at most n as those for which the n-sphere S ⁿ is a Lipschitz extensor. Large scale and small scale analogues of that result are given. The author was partially supported by Grant No.2004047 from the United States-Israel Binational Science Foundation (BSF), Jerusalem, Israel. The author was supported by Grant AP2004-2494 from the Ministerio de Educacion y Ciencia, Spain. He thanks the Department of Mathematics of University of Tennessee for their hospitality.