Competition between DPPC and SDS at the air-aqueous interface

Vibrational sum frequency generation spectroscopy is used to study the interactions of the charged soluble organic surfactant sodium dodecyl sulfate (SDS) with an insoluble 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) monolayer at the air-aqueous interface. Results indicate that the surfactant species compete for surface sites in the mixed system, with a lower monolayer number density of DPPC molecules being observed in the presence of dodecyl sulfate anions at the interface. Spectroscopic results also indicate that fewer dodecyl sulfate chains reside at the interface when the insoluble DPPC film is present. Increased conformational ordering of the acyl chains of both the DPPC molecules and the interfacial dodecyl sulfate anions is observed in the mixed system. Additionally, charged surfactant SDS promotes the alignment of the interfacial water molecules even in the presence of a DPPC monolayer.     

Charge transfer interactions in polymers and the fabrication of high frequency electro-optic modulators

The synthesis and processing of second order nonlinear optical polymeric materials for application in electro-optic devices is described with particular emphasis on (1) the synthesis and incorporation into hardened polymer lattices of chromophores characterized by large μβ (where μ is the dipole moment and β is the molecular first hyperpolarizability) values; (2) the synthesis and incorporation into hardened polymer lattices of chromophores which are capable of undergoing photo-induced conformational changes and which can be processed by new multi-color photolithography techniques into buried channel active waveguides; and (3) the processing of polymeric nonlinear optical materials appropriate for the realization of full integration with very large scale integration (VLSI) drive electronics and with silica fiber optic transmission lines. Prototype modulators have been fabricated and shown to be suitable for broadband operation from 0 to 113 GHz. Optical losses associated with waveguide wall roughness and with mode mismatch in transitioning between silica and polymeric waveguides are reduced by control of the conditions of reactive ion etching and by use of the new technique of multi-color photochemical lithography.     

Cosmological evolution of interacting dark energy in Lorentz violation

The cosmological evolution of an interacting scalar-field model in which the scalar field interacts with dark matter, radiation, and baryons via Lorentz violation is investigated. We propose a model of interaction through the effective coupling, [`(b)]\bar{\beta} . Using dynamical system analysis, we study the linear dynamics of an interacting model and show that the dynamics of critical points are completely controlled by two parameters. Some results can be mentioned as follows. Firstly, the sequence of radiation, the dark matter, and the scalar-field dark energy exist and baryons are subdominant. Secondly, the model also allows for the possibility of having a universe in the phantom phase with constant potential. Thirdly, the effective gravitational constant varies with respect to time through [`(b)]\bar{\beta} . In particular, we consider the simple case where [`(b)]\bar{\beta} has a quadratic form and has a good agreement with the modified ΛCDM and quintessence models. Finally, we also calculate the first post-Newtonian parameters for our model.     

Boundedness of Convolution Operators and Input–Output Maps between Weighted Spaces

We ask when convolution operators with scalar- or operator-valued kernel functions map between weighted L² spaces of Hilbert space-valued functions. For a certain class of decreasing weights, including negative powers (t + a)^−m for example, we solve the one-weight problem completely by using Laplace transforms and Bergman-type spaces of vector-valued analytic functions. For a much more general class of decreasing weights, we solve the one-weight problem for all positive real kernels (also for L^p(w) with p > 1), by results on Steklov operators which generalise the weighted Hardy inequality. When the kernel function is a strongly continuous semigroup of bounded linear Hilbert space operators, which arises from input–output maps of certain linear systems, then the most obvious sufficient condition for boundedness, obtained by taking norm signs inside the integrals, is also necessary in many cases, but not in general. Submitted: July 15, 2007.,Revised: November 19, 2007.,Accepted: December 14, 2007.     

An electrochemical cell coupled with disposable screen-printed electrodes for use in flow injection analysis.

An electrochemical cell coupled with disposable screen-printed electrodes (SPEs) that is specifically designed for use in flow injection analysis (FIA) is described in this study. The cell is made of foldable polyoxymethylene (acetal) thick platelets with the bottom portion consisting of a cavity track to drag the SPEs in position and the top portion having predrilled T-like holes to arrange the Ag/AgCl reference electrode and stainless steel inlet & outlet. An "O ring" is suitably fixed on the top of the working electrode to form a thin-layer space where the electrochemical reaction can take place. Hydrodynamic characterization was validated by using a benchmark hexacyanoferrate redox couple. The results of practical analysis of glucose in human plasma clearly demonstrate the characteristics and applicability of the proposed wall-jet electrochemical cell in FIA.     

Characterizing challenging microcrystalline solids with solid-state NMR shift tensor and synchrotron X-ray powder diffraction data: structural analysis of ambuic acid

Synchrotron X-ray powder diffraction and solid-state (13)C NMR shift tensor data are combined to provide a unique path to structure in microcrystalline organic solids. Analysis is demonstrated on ambuic acid powder, a widely occurring natural product, to provide the complete crystal structure. The NMR data verify phase purity, specify one molecule per asymmetric unit, and provide an initial structural model including relative stereochemistry and molecular conformation. A refinement of X-ray data from the initial model establishes that ambuic acid crystallizes in the P2(1) space group with unit cell parameters a = 15.5047(7), b = 4.3904(2), and c = 14.1933(4) A and beta = 110.3134(3) degrees . This combined analysis yields structural improvements at two dihedral angles over prior NMR predictions with differences of 103 degrees and 37 degrees found. Only minor differences of +/-5.5 degrees , on average, are observed at all remaining dihedral angles. Predicted hydroxyl hydrogen-bonding orientations also fit NMR predictions within +/-6.9 degrees . This refinement corrects chemical shift assignments at two carbons and reduces the NMR error by approximately 16%. This work demonstrates that the combination of long-range order information from synchrotron powder diffraction data together with the accurate shorter range structure given by solid-state NMR measurements is a powerful tool for studying challenging organic solids.     

Using an electrical potential to reversibly switch surfaces between two states for dynamically controlling cell adhesion

Smart surfaces presenting both antifouling molecules with a charged functional group at their distal end, and molecules that are terminated by RGD peptides for cell adhesion, were fabricated and characterized (see picture). By applying potentials of +300 or -300?mV, the surfaces could be dynamically switched to make the peptide accessible or inaccessible to cells.     

Gas‐flow assisted ion transfer for mass spectrometry

Methods and devices that use gas flows to collect ions and transfer them over long distances for mass spectrometric analysis have been developed. Gas flows derived from the ionization source itself or provided by means of additional pumping were used to generate a laminar flow inside cylindrical tube. Hydrodynamic simulations and experimental tests demonstrate that laminar flow can transfer ions over long distance. The typical angular discrimination effects encountered when sampling ions from ambient ionization sources are minimized, and the sampling of relatively large surface areas is demonstrated with desorption electrospray ionization (DESI). Ion transfer over 6 m has been achieved and its application to multiplexed chemical analysis is demonstrated on samples at locations remote from the mass spectrometer. Copyright © 2012 John Wiley & Sons, Ltd.