Surface-functionalized fluorescent silica nanoparticles for the detection of ATP

The design of two-dyed fluorescent silica nanoparticles for ATP detection is presented. The indicator dye possesses a dipicolyl-amine (DPA) unit complexed with Zn(II) as a receptor function for ATP while a rhodamine derivative is used as the reference dye. The nanoparticles were fully characterized regarding analytical performance, morphology and cytocompatibility.     

Lipothiophosphoramidates for gene delivery: critical role of the cationic polar headgroup

When considering a family of cationic lipids designed for gene delivery, the nature of the cationic polar head probably has a great influence on both the transfection efficacy and toxicity. Starting from a cationic lipothiophosphoramidate bearing a trimethylammonium headgroup, we report herein the impact on gene transfection activity of the replacement of the trimethylammonium moiety by a trimethylphosphonium or a trimethylarsonium group. A series of three different human epithelial cell lines were used for the experimental transfection studies (HeLa, A549 and 16HBE14o(-)). The results basically showed that such structural modifications of the cationic headgroup can lead to a high transfection efficacy at low lipid/DNA charge ratios together with a low cytotoxicity. It thus appears that the use of a trimethylarsonium cationic headgroup for the design of efficient gene carriers, which was initially proposed in the lipophosphoramidate series, can be extended to other series of cationic lipids and might therefore have great potential for the development of novel non-viral vectors in general.     

Solid friction from stick–slip down to pinning and aging

We review the present state of understanding of solid friction at low velocities and for systems with negligibly small wear effects. We first analyze in detail the behavior of friction at interfaces between macroscopic hard rough solids, whose main dynamical features are well described by the Rice–Ruina rate and state-dependent constitutive law. We show that it results from two combined effects: (i) the threshold rheology of nanometer-thick junctions jammed under confinement into a soft glassy structure and (ii) the geometric aging, i.e. slow growth of the real area of contact via asperity creep interrupted by sliding. Closer analysis leads to identifying a second aging-rejuvenation process, at work within the junctions themselves. We compare the effects of structural aging at such multicontact, very highly confined, interfaces with those met under different confinement levels, namely boundary lubricated contacts and extended adhesive interfaces involving soft materials (hydrogels, elastomers). This leads us to propose a classification of frictional junctions in terms of the relative importance of jamming and adsorption-induced metastability.

Solid friction from stick–slip down to pinning and aging

All authors

Tristan Baumberger &; Christiane Caroli

https://doi.org/10.1080/00018730600732186

Published online:

28 November 2010

Table     

Diffraction study of actinides under pressure

Abstract

Uranium and thorium have sufficiently low radioactive dose rates to allow their study at synchrotrons and neutron facilities. Correspondingly, numerous compounds of these two actinides have been studied under pressure by synchrotron x-ray diffraction. The maximum pressures reached were on the order of 60-80 GPa, and 300 GPa in one case.

The situation is much more difficult for all other actinides. Their high level of radioactivity has up to now prevented their study at synchrotrons, except in a few special cases. In contrast, all actinide metals available in sufficient quantities, and a large number of compounds of highly radioactive actinides, have been studied in highpressure laboratory facilities.

Recent examples of in situ high pressure x-ray diffraction work will be described.     

Embedded Surfaces of Arbitrary Genus Minimizing the Willmore Energy Under Isoperimetric Constraint

The isoperimetric ratio of an embedded surface in ${\mathbb{R}^3}$ is defined as the ratio of the area of the surface to power three to the squared enclosed volume. The aim of the present work is to study the minimization of the Willmore energy under fixed isoperimetric ratio when the underlying abstract surface has fixed genus ${g \geqq 0}$ . The corresponding problem in the case of spherical surfaces, that is g = 0, was recently solved by Schygulla (see Schygulla, Arch Ration Mech Anal 203:901–941, 2012) with different methods.     

valuation of options on joint minima and maxima

It is shown how to obtain explicit formulae for a variety of popular path-dependent contracts with complex payoffs involving joint distributions of several extrema. More specifically, formulae are given for standard step-up and stepdown barrier options, as well as partial and outside step-up and step-down barrier options, between three and five dimensions. The proposed method can be extended to other exotic path-dependent payoffs as well as to higher dimensions. Numerical results show that the quasi-random integration of these formulae, involving multivariate distributions of correlated Gaussian random variables, provides option values more quickly and more accurately than Monte Carlo simulation.     

Single-frequency Brillouin distributed feedback fiber laser

We demonstrate a single-frequency Brillouin distributed feedback laser (DFB). The DFB laser cavity was a 12.4 cm long fiber Bragg grating with a π-phase shift offset from the grating center. It exhibited a threshold of 30 mW and conversion efficiency from pump to Stokes wave as high as 27%. Higher-order Stokes waves were suppressed by more than 20 dB. The Stokes output of the laser could be obtained in either the forward or backward direction, simply by changing the orientation of the offset of the discrete phase shift with respect to the pump propagation direction. The DFB laser operated over a pump frequency range of 1.2 GHz, more than 60 times larger than the SBS gain bandwidth.     

Frictional dissipation and interfacial glass transition of polymeric solids

We present single contact friction experiments between a glassy polymer and smooth silica substrates grafted with alkylsilane layers of different coverage densities and morphologies. This allows us to adjust the polymer-substrate interaction strength. We find that, when going from weak to strong interaction, the response of the interfacial junction where shear localizes evolves from that of a highly viscous threshold fluid to that of a plastically deformed glassy solid. This we analyze as resulting from an interaction-induced "interfacial glass transition" helped by pressure.     

Electrophotocatalysis with a Trisaminocyclopropenium Radical Dication

Visible‐light photocatalysis and electrocatalysis are two powerful strategies for the promotion of chemical reactions. Here, these two modalities are combined in an electrophotocatalytic oxidation platform. This chemistry employs a trisaminocyclopropenium (TAC) ion catalyst, which is electrochemically oxidized to form a cyclopropenium radical dication intermediate. The radical dication undergoes photoexcitation with visible light to produce an excited‐state species with oxidizing power (3.33 V vs. SCE) sufficient to oxidize benzene and halogenated benzenes via single‐electron transfer (SET), resulting in C?H/N?H coupling with azoles. A rationale for the strongly oxidizing behavior of the photoexcited species is provided, while the stability of the catalyst is rationalized by a particular conformation of the cis‐2,6‐dimethylpiperidine moieties.     

Interplay Between J‐ and H‐Type Coupling in Aggregates of π‐Conjugated Polymers: A Single‐Molecule Perspective

Strong dipole–dipole coupling within and between π‐conjugated segments shifts electronic transitions, and modifies vibronic coupling and excited‐state lifetimes. Since J‐type coupling between monomers along the conjugated‐polymer (CP) chain and H‐type coupling of chromophores between chains of a CP compete, a superposition of the spectral modifications arising from each type of coupling emerges, making the two couplings hard to discern in the ensemble. We introduce a single‐molecule H‐type aggregate of fixed spacing and variable length of up to 10 nm. HJ‐type aggregate formation is visualized intuitively in the scatter of single‐molecule spectra.