Surface-induced dissociation of protonated peptides: implications of initial kinetic energy spread.

Surface-induced dissociation (SID) has been used to produce daughter ion spectra of small protonated peptides generated by fast atom bombardment (FAB). The relative abundances of daughter ions depends critically upon the energy of the ion/surface collision. A wide array of decomposition processes may be observed using ELAB collision energies in the range 10-20 eV. At approximately 13-eV collision energy, the variety of decomposition processes is maximized for the small peptides studied; hence, maximum structural information may be deduced. Collisionally-activated dissociations (CAD) using argon gas and the identical protonated peptides could not produce as large an array of daughter ions in a constant condition experiment. An apparent contradiction is thereby posed because SID is known to produce a narrow distribution of ion internal energies relative to CAD. This apparent contradiction is resolved by considering the rather large kinetic energy spread of ions leaving the FAB source. For the SID process, this large initial kinetic energy distribution is converted into a significantly wider spread in center-of-mass collision energy, leading to a broader variety of decomposition processes (high and low energy) compared to CAD.     

Effect of tantalum addition on microstructure and optical properties of TiN thin films

Titanium nitride thin films were deposited by direct current magnetron sputtering with various tantalum (Ta) concentrations (2, 4 and 8 at.%). The films were characterized using UV/VIS spectrophotometer. Atomic force microscopy (AFM), high resolution transmission electron microscope (HRTEM) were used to observe the microstructure and X-ray photoelectron spectroscopy was used to investigate the core level and the valence band of the films. It was found that the film with 2 at.% Ta is more reflective in the infrared range and more transparent in the visible region (selective behavior). The AFM showed smooth nanostructured surface for the film without Ta addition. It was found that the films with 2 at.% Ta presented relatively coarser grains with larger roughness and the reflectance are not controlled by the surface morphology. Also, this film presented higher electrical conductivity. HRTEM analysis showed that 2 at.% Ta addition gave rise to well crystallized films with elongated nanocrystallites in comparison with the films having 0, 4 and 8 at.% Ta contents.     

A cluster-based trust-aware routing protocol for mobile ad hoc networks

Routing protocols are the binding force in mobile ad hoc network (MANETs) since they facilitate communication beyond the wireless transmission range of the nodes. However, the infrastructure-less, pervasive, and distributed nature of MANETs renders them vulnerable to security threats. In this paper, we propose a novel cluster-based trust-aware routing protocol (CBTRP) for MANETs to protect forwarded packets from intermediary malicious nodes. The proposed protocol organizes the network into one-hop disjoint clusters then elects the most qualified and trustworthy nodes to play the role of cluster-heads that are responsible for handling all the routing activities. The proposed CBTRP continuously ensures the trustworthiness of cluster-heads by replacing them as soon as they become malicious and can dynamically update the packet path to avoid malicious routes. We have implemented and simulated the proposed protocol then evaluated its performance compared to the clustered based routing protocol (CBRP) as well as the 2ACK approach. Comparisons and analysis have shown the effectiveness of our proposed scheme.     

Study of the Mechanical Properties of Fibers Extracted from Tunisian Agave americana L.

Agave americana L. fibers, the most abundant variety in Tunisia, have a quite important textile potential. This potential is demonstrated by studying the extraction of these fibers from leaves, their physical properties such us fineness or density and their mechanical behavior in tensile tests. In this work, results of a mechanical behavior study of fibers extracted from the Agave americana L. plant are presented. These results deal with the principal and mechanical characteristics of these fibers which are the strain at break, the elasticity modulus and the rupture facture. These results permitted to situate these fibers, compared to the other textile fibers, as materials that can be used in technical applications such as reinforcing composites or geotextile. In order to understand the mechanical properties of these fibers, a correlation study between the properties already cited and the fine structure was done. The obtained results showed that the mechanical properties of Agave americana L. fibers are closely related to the individual fibers deformations and to the natural matrix (lignin and gums) that are linked to these elementary fibers.     

Development of artificial neural networks for real time, in situ ellipsometry data reduction

Development of real time in situ monitoring and control of thin film depositions using ellipsometry requires both data acquisition and processing to be rapid. Present speeds of measurement and computation of basic parameters, Ψ and Δ, are sufficient for data acquisition which is essentially real time. However, computation of film parameters, such as thickness and optical properties, generally cannot keep up with the incoming data and must be performed in a batch mode after the deposition.

This work describes the development of enhanced, high speed data reduction algorithms using artificial neural networks (ANN). The networks are trained using computed data and subsequently give values of film parameters in the millisecond time regime. The ANN outputs are used as initial estimates in a variably damped least squares algorithm for accuracy improvement. The combination of these two algorithms provides very accurate solutions in 75 ms per point on a DEC VAX 8800 multiprocessor system running at a combined 12 Mips. This speed is suitable for real time film monitoring and control for growth rates up to 10 nm per second. Results for fixed angle of incidence, single wavelength, in situ data for Ni deposited on BK7 substrates are presented.     

Coupling 2D SDS-PAGE with CNBr cleavage and MALDI-TOFMS: a strategy applied to the identification of proteins induced by a hypochlorous acid stress in Escherichia coli

A protocol including 2D SDS-PAGE, electroblotting proteins onto nitrocellulose membranes, and CNBr cleavage, followed by MALDI-MS analysis of intact proteins and peptide fragments and a database search, has been optimized and applied to the rapid identification of the Escherichia coli response to hypochlorous acid. The methodology has proved to be efficient from the point of view of sensitivity (picomole range) and selectivity. In particular, MALDI analysis of proteins and CNBr fragments by directly dissolving the membrane in an acetone solution of matrix, without previous elution, is reliable and reproducible. The accuracy of the MW determination is somewhat reduced compared to that of methods involving elution and purification of proteins and digests; nevertheless, the utilization of large MW windows combined with the pI entry in database searches had allowed, for most of the spots, the selection of only one protein candidate. Finally, 19 proteins exhibiting a response to hypochlorous acid stress have been confirmed or identified on the basis of this protocol.     

Customizing MRI-Compatible Multifunctional Neural Interfaces through Fiber Drawing

Fiber drawing enables scalable fabrication of multifunctional flexible fibers that integrate electrical, optical, and microfluidic modalities to record and modulate neural activity. Constraints on thermomechanical properties of materials, however, have prevented integrated drawing of metal electrodes with low-loss polymer waveguides for concurrent electrical recording and optical neuromodulation. Here, two fabrication approaches are introduced: 1) an iterative thermal drawing with a soft, low melting temperature (T_m) metal indium, and 2) a metal convergence drawing with traditionally non-drawable high T_m metal tungsten. Both approaches deliver multifunctional flexible neural interfaces with low-impedance metallic electrodes and low-loss waveguides, capable of recording optically-evoked and spontaneous neural activity in mice over several weeks. These fibers are coupled with a light-weight mechanical microdrive (1 g) that enables depth-specific interrogation of neural circuits in mice following chronic implantation. Finally, the compatibility of these fibers with magnetic resonance imaging is demonstrated and they are applied to visualize the delivery of chemical payloads through the integrated channels in real time. Together, these advances expand the domains of application of the fiber-based neural probes in neuroscience and neuroengineering.