1,720,990 research outputs found
Highly efficient non-biofouling coating of zwitterionic polymers: Poly((3-(methacryloylamino)propyl)-dimethyl(3-sulfopropyl)ammonium hydroxide)
No full textThis work describes the formation of highly efficient non-biofouling polymeric thin films of poly((3-(methacryloylamino)propyl)-dimethyl(3-sulfopropyl)ammonium hydroxide), (poly(MPDSAH)). The poly(MPDSAH) films were generated from the self-assembled monolayers terminating in an initiator of atom transfer radical polymerization (ATRP) by the surface-initiated ATRP of MPDSAH. The poly(MPDSAH) films on a gold surface were characterized by ellipsometry, FT-IR spectroscopy, contact angle goniometery, and X-ray photoelectron spectroscopy. The copper complexes and unpolymerized monomers trapped inside the polymer brushes were completely washed out by soaking the poly(MPDSAH)-coated substrate in water at 40 degrees C for 4 days. The amount of proteins nonspecifically adsorbed onto the poly(MPDSAH) films was evaluated by surface plasmon resonance spectroscopy: the adsorption of proteins was < 0.6 ng/cm(2) on the surfaces for all the model proteins. The ability of the poly(MPDSAH) films to resist the nonspecific adsorption of proteins was comparable to that of the best known systems
Spin-orbit density functional theory calculations for (X = F, Cl, Br and I) molecules
No full textTwo component spin-orbit density functional theory (SODFT) calculations for spectroscopic constants of IX (X = F, Cl, Br and I) molecules have been performed with several functionals using shape-consistent relativistic effective core potentials (RECPs) with effective one-electron spin-orbit operator. The SODFT results obtained with the B3LYP functional are in very good accord with the results of previous two-component CCSD(T) calculations with the same RECP and basis sets. Results of two-component SODFT calculations with RECPs are also in good agreement with reported all-electron relativistic DFT calculations with the same functionals. The spectroscopic constants obtained with ACM and PBE0 functionals display the best agreement with the experimental values among the functionals tested. Spin-orbit effects from the SODFT calculations result in increases of bond lengths and decreases of dissociation energies and harmonic vibrational frequencies and the magnitudes are in reasonable agreement with those from two-component CCSD(T) calculations. Spin-orbit effects appear to be quite insensitive to the choice of functionals for the bond lengths and harmonic vibrational frequencies, but those of the dissociation energies somewhat deviate with the differing class of functionals
Fabrication of Hairy Polymeric Films Inspired by Geckos: Wetting and High Adhesion Properties
No full textIn this paper, we report a facile and efficient method for fabricating gecko-inspired, hairy hard poly(dimethylsiloxane) (h-PDMS) structures, composed of nanopillars with controllable lengths. The structures are generated by utilizing an anodic aluminum oxide (AAO) membrane as a replication template. For easy handling of the replicated h-PDMS films, the vinyl-terminated glass substrate is used. The cross-linking between the vinyl moieties on the glass surface and methylhydrosiloxanes, one of the h-PDMS components, makes it easy to transfer the molded h-PDMS layer from the AAO template to the glass. The resulting hairy h-PDMS-coated glass surface shows both the static water contact angle as high as 150.5 degrees +/- 0.4 degrees (superhydrophobicity) and high adhesion to water. A water droplet placed on the h-PDMS surface does not slide, even when the surface is tilted vertically or turned upside down. We believe that the densely packed h-PDMS nanopillars (2.6 x 10(6) pillars mm(-2)) are the key contributor to the observed high adhesion, presumably by generating large van der Waals' forces from the large surface area in very close contact with water. The adhesion force of the surface is found to be strong enough to catch a water droplet that rolls down fast on a tilted self-cleaning surface. In addition to water, the wetting and high adhesion properties of the molded nanopillar h-PDMS films are also investigated with several organic liquids
Effect of secretin on intracellular pH regulation in isolated rat bile duct epithelial cells.
No full textThe effects of secretin on ion transport mechanisms involved in regulation of intracellular pH (pHi) and HCO3- excretion were characterized in bile duct epithelial (BDE) cells isolated from normal rat liver. pHi was measured with 2,7-bis(carboxy-ethyl)-5(6)-carboxy-fluorescein-acetomethylester (BCECF-AM) using a microfluorimetric method. Basal pHi of BDE was 7.04 +/- 0.06 in Hepes and 7.16 +/- 0.10 in KRB and was unaffected by secretin (50-200 nM). Recovery rates from an acid load in Hepes or in KRB media (with and without amiloride) were also not altered by secretin, indicating that Na+/H+ exchange and Na+/HCO3- cotransport were not affected by this hormone. After acute Cl- removal, pHi rose 0.24 +/- 0.08 pHU at a maximal rate of 0.125 +/- 0.06 pHU/min (H+ flux rates = 6.02 +/- 3.27 mM/min) and recovered after Cl- readmission (0.188 +/- 0.08 pHU/min; H+ flux rates = 11.82 +/- 5.34 mM/min). Pretreatment with 1 mM DIDS inhibited the effects of Cl- removal, while valinomycin, which induces cell depolarization, enhanced these effects, probably by stimulating electrogenic HCO3- influx. Secretin significantly increased both the maximal rate of alkalinization after Cl- removal (P < 0.012) and of pHi recovery after Cl- readmission (P < 0.025), indicating stimulation of Cl-/HCO3- exchange activity. These findings were reproduced with N6,2'-O-Dibutyryladenosine-3',5'-cyclic monophosphate (DBcAMP). The Cl- channel blocker 5-nitro-2'-(3-phenylpropylamino)-benzoate (NPPB, 10 microM) significantly decreased the effects of secretin and DBcAMP on the pHi changes promoted by acute Cl- removal/readmission. These findings establish that secretin stimulates the activity of the Cl-/HCO3- exchanger in BDE cells, probably by activating Cl- channels via the intracellular messenger cAMP. This in turn depolarizes the cell, stimulating electrogenic Na+/HCO3- symport. The cell depolarization induced by Cl- channel activation should enhance HCO3- entrance through electrogenic Na+/HCO3- symport, which in turn stimulates the Cl-/HCO3- exchange. These mechanisms could account for secretin stimulated bicarbonate secretion in bile
DOUBLE-DIFFUSIVE CONVECTION IN A ROTATING ANNULUS WITH HORIZONTAL TEMPERATURE AND VERTICAL SOLUTAL GRADIENTS
No full textA numerical study is made of double-diffusive convection in a rotating annulus. Motions are driven by the externally applied horizontal temperature gradient. The stable solutal gradient is aligned in the vertical direction. Parametric studies are performed in order to acquire an understanding of the qualitative character of the axisymmetric basic state of the resulting flow. The aim is to inquire as to the effect of rotation on the global flow structure. A high-accuracy pseudospectral numerical scheme is employed to integrate the axisymmetric incompressible Navier-Stokes equations. Computational results are presented to disclose the detailed fields of azimuthal and meridional flows, temperature, and solute. A total of nine parameter sets, produced by a combination of three values of stratification number and three buoyancy ratios, were dealt with in the computation. The Prandtl number was set Pr = 1.0, the thermal Rayleigh number Ra(T) = 10(5), and the Lewis number Le = 10.0. For a low buoyancy ratio, motions are vigorous, especially when the rotation effect is small, resembling a sidewall-heated pure thermal convection. In the interior, a linear temperature stratification and a well-mixed solutal field are seen. When the buoyancy ratio is moderate, the overall character of flow shows considerable dependence on the relative strength of rotation effect. For a large buoyancy ratio, the stabilizing solutal effect is dominant. The convective activities are very weak, and heat transfer is mostly conductive
Formation of superhydrophobic surfaces by biomimetic silicification and fluorination
No full textThe amazing water repellency of many biological surfaces, exemplified by lotus leaves, has recently received a great deal of interest. These surfaces, called superhydrophobic surfaces, exhibit water contact angles larger than 150 and a low contact angle hysteresis because of both their low surface energy and heterogeneously rough structures. In this paper, we suggest a biomimetic method, "biosilicification", for generating heterogeneously rough structures and fabricating superhydrophobic surfaces. The superhydrophobic surface was prepared by a combination of the formation of heterogeneously rough, nanosphere-like silica structures through biosilicification and the formation of self-assembled monolayers of fluorosilane on the surface. The resulting surface exhibited the water contact angle of 160.1 and the very low water contact angle hysteresis of only 2.3, which are definite characteristics of superhydrophobic surfaces. The superhydrophobic property of our system probably resulted from the air trapped in the rough surface. The wetting behavior on the surface was in the heterogeneous regime, which was totally supported by Cassie-Baxter equation
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Gold-catalyzed cyanosilylation reaction: Homogeneous and heterogeneous pathways
No full textGold had been considered to be an extremely inert metal, but recently it was found that nanometer-sized gold particles on metal-oxide supports acted as catalysts for simple organic reactions, such as oxidation and hydrogenation, even at or below room temperature. Herein, we report that gold nanoparticles (AuNPs) of zero oxidation state (Au-0) are catalytically active for a C-C bond-forming reaction, the cyanosilylation of aldehydes. ne AuNP-catalyzed cyanosilylation proceeded smoothly at room temperature with 0.2 wt% loading of AuNPs. The reactions of aromatic aldehydes were almost quantitative, except for benzaldehyde derivatives containing the electron-withdrawing NO2 group, and alpha,beta-unsaturated aromatic aldehydes were the most reactive substrates. The reactions also went smoothly for aliphatic aldehydes. Mechanistic studies indicated that the reactions proceeded both homogeneously and heterogeneously: homogeneous catalysis by leached gold species and heterogeneous catalysis by the adsorption of the reactants (aldehydes and trimethylsilyl cyanide) onto AuNPs. The ratio of homogeneous and heterogeneous catalysis was estimated to be approximate to 4:1
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