Probing Ag nanoparticle surface oxidation in contact with (in)organics: an X‐ray scattering and fluorescence yield approach

Characterizing interfacial reactions is a crucial part of understanding the behavior of nanoparticles in nature and for unlocking their functional potential. Here, an advanced nanostructure characterization approach to study the corrosion processes of silver nanoparticles (Ag‐Nps), currently the most highly produced nanoparticle for nanotechnology, is presented. Corrosion of Ag‐Nps under aqueous conditions, in particular in the presence of organic matter and halide species common to many natural environments, is of particular importance because the release of toxic Ag⁺ from oxidation/dissolution of Ag‐Nps may strongly impact ecosystems. In this context, Ag‐Nps capped with polyvinolpyrrolidone (PVP) in contact with a simple proxy of organic matter in natural waters [polyacrylic acid (PAA) and Cl^? in solution] has been investigated. A combination of synchrotron‐based X‐ray standing‐wave fluorescence yield‐ and X‐ray diffraction‐based experiments on a sample consisting of an approximately single‐particle layer of Ag‐Nps deposited on a silicon substrate and coated by a thin film of PAA containing Cl revealed the formation of a stable AgCl corrosion product despite the presence of potential surface stabilizers (PVP and PAA). Diffusion and precipitation processes at the Ag‐Nps–PAA interface were characterized with a high spatial resolution using this new approach.     

Improved rejection of multiply scattered photons in confocal microscopy using dual-axes architecture

We perform Monte Carlo simulations to show that the dual-axes (DA) confocal architecture has superior rejection of multiply scattered photons in tissue to that of single axis. As a result, the DA configuration provides improved signal-to-noise ratio and dynamic range, and thus is sensitive to ballistic photons from deeper within tissue, features that are particularly useful for performing vertical cross-sectional reflectance images in tissue.     

The production and destruction of the C-related 969 meV absorption band in Si

Data are reported on the production of the 969 meV absorption line as functions of the carbon concentration and radiation dose in FZ and CZ silicon. With increasing dose of 2 MeV electrons the absorption first increases and then decreases. Simple equations are presented which describe the growth and decay. It is shown that, in favourable circumtances, carbon concentrations as low as 10¹⁴ cm⁻³ can be detected in silicon by means of the 969 meV absorption line. We verify that the 969 meV line anneals out at temperatures >500 K but may increase between 450 and 500 K. We show that the increase is largest in samples irradiated at room temperature to a small dose relative to the carbon concentration.     

On the projection and macphail constants ofl n p spaces

We prove that the projection and Macphail constants ofl _n ^p (1≦p≦2) are asymptotically equivalent ton ^1/2 andn ^−1/2 respectively. We also obtain some relations linking certain parameters of general finite dimensional real Banach spaces. This note is a part of the author’s Ph.D. Thesis prepared at the Hebrew University of Jerusalem, under the supervision of Prof. J. Lindenstrauss, to whom the author wishes to express his thanks and appreciation.     

Electrochemical methods for analysing and controlling charge transfer at the electrode–tissue interface

There have been rapid advances in the development of new materials for use in electrode–tissue interfacing. The development of conducting polymers, conducting hydrogels, carbon nanotubes, graphene and other conducting materials has provided a rich landscape for controlling charge transfer at the electrode–tissue interface and hence to monitor and manipulate cell behaviour. These materials have been used in tissue-engineered constructs to direct and control cell proliferation, growth and differentiation. However, their translation to clinical devices has been less successful. In this review, the use of electroanalytical techniques to develop an understanding of charge transfer at the electrode–tissue interface is discussed. In particular, the impact of solution and electrode conditions on charge injection capacity is demonstrated. The importance of standardised testing methods and the correlation of electrochemical and electrophysiological performance show the limitations of empirical studies and help define key electrode properties for clinical devices. The development of a sound theoretical basis for charge transfer at this increasingly important interface is being advocated to improve clinical outcomes and device lifetime and reduce power usage.     

Determination of work functions near melting points of refractory metals by using a direct-current arc

A direct-current arc in argon at atmospheric pressure was used to determine effective work functions of refractory metals, including tantalum, tungsten, molybdenum, and niobium. The procedure is experimentally advantageous because surface cleanliness of the specimen is not critical, high vacuum is not required, and the anode-cathode spacing is not critical. The experimental procedure involves striking an arc to a metal wire cathode to form a melted ball having an emitting area defined by its diameter. The literature melting point of the metal is taken as the emitting temperature. By using these parameters and the known arc current, effective work functions were calculated from the Richardson-Dushman equation. The calculated work functions agree with recommended handbook values to within about 0.1 V and have typical repeatabilities of 0.02 V. By varying the arc current, Richardson plots can be made over a temperature range from a few hundred degrees below the melting point to about 50° over the melting point of the test metal. A Richardson plot over this temperature range is presented for tantalum.     

Matroids over fp which are rational excluded minors

For a given prime p, we construct a collection of 2^p matroids G_p,a with (1) χ_pf(G_p,a)={p}, and (2) G_p,a is an excluded minor for rational representability. The motivating construction (Section 2) disproves a conjectures of Reid [4], using relatively high-rank, high cardinality matroids. The general construction (Section 3) makes use of ordered partitions (χ_pf(G) denotes the prime-field characteristic set of G, i.e., the set of prime fields over which G may be represented, while G can be represented over fields of no other characteristic.) Finally, Section 4 offers another construction with the same properties–a kind of projective dual to Section 2.     

Synthesis of N-alkyl substituted bioactive indolocarbazoles related to Gö6976

The syntheses of new nitrile and amide analogues of 7-keto Gö6976 are described. The amide analogue 22 was formed via the condensation with a new functionalized indoleacetic acid derivative 25 to overcome the solubility problem during the coupling reaction.