Atomic force microscopy (AFM) characterisation of the porous silica nanostructure of two centric diatoms

The porous silica nanostructure of two marine, centric diatoms, Coscinodiscus sp. and Thalassiosira eccentrica was investigated by atomic force microscopy (AFM). Important morphological features of the silica frustules of diatoms are described, including: the organisation of porous silica layers, their topography, pore size, shape and density. The outer layer of Coscinodiscus sp., commonly called the cribellum, consists of a characteristic hexagonal array of pores with pore sizes of around 45 nm. This thin membrane covers a second structural layer where two different silica surfaces are identified. The outer part, known as the cribrum consists of hexagonally packed pores of about 200 nm diameter. The inner part, known as the foramen layer, consists of larger and radially distributed holes with a diameter of around 1,150 nm. The second diatom species investigated, T. eccentrica produces a frustule with one silica structural layer featuring two different porous surfaces. The outer surface has large (800 nm diameter) holes (foramen) while the inner surface contains a porous wall with pores comparable in size to the Coscinodiscus sp. cribellum. The inner and outer surfaces of the frustule wall of both diatoms are hence in reverse order. However, the size of the small pores is similar for both species. High-resolution AFM also revealed the granular nanostructure of the diatom biosilica with grain sizes from 20 to 70 nm diameters.     

High-Density Solder Bump Interconnect for MEMS Hybrid Integration

An ultra high-density hybrid integration for micro-electromechanical system (MEMS) mirror chips with several thousand inputs/outputs has been developed. The integration scheme involving flip-chip assembly provides electrical signal to individual mirrors, which is compatible with postprocessing steps of selectively removing the silicon handle and releasing the MEMS mirrors. For the first time, to our knowledge, solder deposition and flip-chip bonding of 3-mum bumps on 5-mum centers of a large array has been demonstrated.     

Electronic properties of carbon nanotubes calculated from density functional theory and the empirical <Emphasis Type="Italic">π</Emphasis>-bond model

The validity of the DFT models implemented by FIREBALL for CNT electronic device modeling is assessed. The effective masses, band gaps, and transmission coefficients of semi-conducting, zigzag, (n,0) carbon nanotubes (CNTs) resulting from the ab-initio tight-binding density functional theory (DFT) code FIREBALL and the empirical, nearest-neighbor π-bond model are compared for all semiconducting n values 5≤n≤35. The DFT values for the effective masses differ from the π-bond values by ±9% over the range of n values, 17≤n≤29, most important for electronic device applications. Over the range 13≤n≤35, the DFT bandgaps are less than the empirical bandgaps by 20–180 meV depending on the functional and the n value. The π-bond model gives results that differ significantly from the DFT results when the CNT diameter goes below 1 nm due to the large curvature of the CNT. The π-bond model quickly becomes inaccurate away from the bandedges for a (10,0) CNT, and it is completely inaccurate for n≤8.     

The professionalisation paths of hackers in IT security: The sociology of a divided identity

This article analyses the professionalisation paths pursued by hackers. More specifically, it focuses on the group of those who became socialised as enthusiastic fans of security between 1995 and 2002. The analysis of paths shows that there are four professional routes: integration as an employee, opting to be independent, the path of fraud and parallel remuneration under a masked identity. These paths progressively reflect the procedures for building a divided identity. Either the hacker transforms himself into a security professional through a change of mentality. Or he develops a split identity, by fragmenting his professional identity. Finally, the article highlights two key parameters explaining the orientation towards one or other of these two forms of divided identity: the internalisation of a code of professional practice, a professional ethic and moderation of strategies to build a media reputation.     

A different approach to implement an active input current shaper

In recent years, several AC/DC converters have been presented in order to meet the power quality regulations, while maintaining the lowest number of components with the purpose of minimizing the cost and complexity; for this purpose the active input current shaping technique was proposed. A new active input current shaper (AICS) is presented. Differently from the traditional series AICS, the proposed scheme connects the auxiliary output of the main converter in parallel with the rectified AC mains instead of the series connection. The proposed parallel scheme demands a current with a low harmonic content where the standard specifications are fulfilled. The operation, simulation, and experimental results of the proposed scheme are presented.     

Bond-coating in plasma-sprayed calcium-phosphate coatings

In the online and printed versions of the original article, there was a typographical error in I. Peker’s name. His name is spelled correctly above. This error occurred in both the html and pdf versions of the online article. The online version of the original article can be found at     

Characterization of Functional Groups of Asphaltenes in Vacuum Residues Using Molecular Modelling and FTIR Techniques

Asphaltenes are components of crude oil, and their average chemical structures are characterized with difficulty. This study shows that simple Fourier transform infrared (FTIR) analysis spectroscopy could be adapted to the determination of aromatic hydrogens in asphaltenes and resins and elucidation of their average molecules. The work demonstrates the existence of a linear correlation in the infrared (IR) intensities of the symmetric and asymmetric aromatic hydrogens in methyl substituted arenes, in the 2,900 to 3,100 cm^-1 region and of the out-of-plane deformation in the 700 to 900 cm^-1 region.     

How to Create Complex FDTD FORTRAN and C Codes Simply with MATHEMATICA

In this paper, we show how the symbolic capabilities of the commercial package MATHEMATICA can be used to facilitate the generation of FORTRAN and C codes to solve Maxwell's differential equations in the time domain with finite-difference schemes.