Charge transfer in Cr adsorption and reaction at the rutile TiO2(110) surface

The rutile TiO2(110) surface has been doped with sub-monolayer metallic Cr, which oxidises and donates charge to specific surface Ti ions. X-Ray and ultra violet photoemission spectroscopy and first principles density functional theory with Hubbard U are used to assign the oxidation states of Cr and surface Ti and we find that Cr2+ forms on bridging oxygen ions and a 5-fold coordinated surface Ti atom is reduced to Ti3+ and the Cr ions readily react with oxygen (to Cr3+), which leads to depletion of surface Ti3+ 3d electrons.

Exploring carrier agents in swarm-array computing

How can a bridge be built between autonomic computing approaches and parallel computing systems? The work reported in this paper is motivated towards bridging this gap by proposing a swarm-array computing approach based on ‘Intelligent Agents’ to achieve autonomy for distributed parallel computing systems. In the proposed approach, a task to be executed on parallel computing cores is carried onto a computing core by carrier agents that can seamlessly transfer between processing cores in the event of a predicted failure. The cognitive capabilities of the carrier agents on a parallel processing core serves in achieving the self-ware objectives of autonomic computing, hence applying autonomic computing concepts for the benefit of parallel computing systems. The feasibility of the proposed approach is validated by simulation studies using a multi-agent simulator on an FPGA (Field-Programmable Gate Array) and experimental studies using MPI (Message Passing Interface) on a computer cluster. Preliminary results confirm that applying autonomic computing principles to parallel computing systems is beneficial.

A cluster-based implementation of a fault-tolerant parallel reduction algorithm using swarm-array computing

Recent research in multi-agent systems incorporate fault tolerance concepts. However, the research does not explore the extension and implementation of such ideas for large scale parallel computing systems. The work reported in this paper investigates a swarm array computing approach, namely ‘Intelligent Agents’. In the approach considered a task to be executed on a parallel computing system is decomposed to sub-tasks and mapped onto agents that traverse an abstracted hardware layer. The agents intercommunicate across processors to share information during the event of a predicted core/processor failure and for successfully completing the task. The agents hence contribute towards fault tolerance and towards building reliable systems. The feasibility of the approach is validated by simulations on an FPGA using a multi-agent simulator and implementation of a parallel reduction algorithm on a computer cluster using the Message Passing Interface.

Infrared filters for space-flight focal plane array applications

Infrared filters and coatings have been employed on many sensing radiometer instruments to measure the thermal emission profiles and concentrations of certian chemical constituents found in planetary atmospheres. The High Resolution Dynamics Limb Sounder ( HIRDLS) is an example of the most recent developments in limb-viewing radiometry by employing a cooled focal plane detector array to provide simultaneous multi-channel monitoring of emission from gas and aerosols over an altitude range between 8 - 70 km. The use of spectrally selective cooled detectors in focal plane arrays has simplified the optical layout of radiometers, greatly reducing the number of components in the optical train. this has inevitably led to increased demands for the enviromnetal durability of the focal plane filters because of the need to cut sub-millimeter sizes, whilst maintaining an optimal spectral performance. Additionally the remaining refractive optical elements require antireflection coatings which must cover the entire spectral range of the focal plane array channels, in this case 6 to 18µm, with a minimum of reflection and absorption. This paper describes the optical layout and spectral design requirements for filteriong in the HIRDLS instrument, and reports progress on the manufacturing and testing of the sub-millimetre sized cooled filters. We also report on the spectral and environmental performance of prototype wideband antireflection coatings which satisfy the requirements above.

High-performance infrared filters for the HIRDLS 21-channel focal plane detector array

The High Resolution Dynamics Limb Sounder is described, with particular reference to the atmospheric measurements to be made and the rationale behind the measurement strategy. The demands this strategy places on the filters to be used in the instrument and the designs to which this leads to are described. A second set of filters at an intermediate image plane to reduce "Ghost Imaging" is discussed together with their required spectral properties. A method of combining the spectral characteristics of the primary and secondary filters in each channel are combined together with the spectral response of the detectors and other optical elements to obtain the system spectral response weighted appropriately for the Planck function and atmospheric limb absorption. This method is used to demonstrate whether the out-of-band spectral blocking requirement for a channel is being met and an example calculation is demonstrated showing how the blocking is built up for a representative channel. Finally, the techniques used to produce filters of the necessary sub-millimetre sizes together with the testing methods and procedures used to assess the environmental durability and establish space flight quality are discussed.

Detecting the number of signals using antenna array: a single threshold solution

A new approach is presented to identify the number of incoming signals in antenna array processing. The new method exploits the inherent properties existing in the noise eigenvalues of the covariance matrix of the array output. A single threshold has been established concerning information about the signal and noise strength, data length, and array size. When the subspace-based algorithms are adopted the computation cost of the signal number detector can almost be neglected. The performance of the threshold is robust against low SNR and short data length.

Avaliação da biocompatibilidade e da propriedade bactericida de nanotubos de dióxido de titânio impregnados com lectina e nanopartículas de prata para aplicações biomédicas

O titânio e suas ligas são os materiais mais comumente utilizados na substituição de tecidos duros por possuírem resistência mecânica, biocompatibilidade, resistência à corrosão e fácil manipulação. Embora o titânio possua várias vantagens sobre outros biomateriais, seu uso em longo prazo pode ocasionar problemas de rejeição. A modificação da superfície do titânio a fim de criar microrrugosidades é uma estratégia efetiva para melhorar a adesão e proliferação celular sobre implantes. Quando um implante danifica ou invade as barreiras epitelial e das mucosas, pode servir como reservatório para microrganismos e desta forma predispor à infecção. Neste sentido, o objetivo deste trabalho foi modificar a superfície do titânio, utilizando nanopartículas de prata (Ag) e lectina, a fim de melhorar a sua biocompatibilidade e conferir propriedades antimicrobianas a este material. O racional por trás destas mudanças é que a criação de uma topografia em nanoescala pode contribuir para mimetizar o ambiente celular melhorando a osseointegração e diminuindo o risco de infecção. Em nosso estudo, nanotubos de dióxido de titânio (NTs-TiO2) com estrutura bem distribuída e organizada, com diâmetro em torno de 70–80nm, foram sintetizados por anodização eletroquímica e decorados com nanopartículas de Ag usando a técnica de layer-by-layer (LbL), enquanto a lectina do peixe Oreochromis niloticus (OniL) foi incorporada aos NTs-TiO2 por spin coating. Estas amostras foram caracterizadas e avaliadas quanto a sua citotoxidade, adesão celular, potencial osteogênico e atividade bactericida. Nossos resultados mostraram que tanto as nanopartículas de Ag, como a Onil foram incorporadas com sucesso à superfície dos NTs-TiO2. Entretanto nossas preparações de LbL não foram capazes de melhorar a biocompatibilidade ou inibir o crescimento de bactérias nos NTs-TiO2. Por outro lado, a funcionalização dos NTs-TiO2 com a OniL induziu eficientemente a adesão e proliferação dos osteoblastos. Nossos resultados apontam para o uso da lectina OniL para melhorar a qualidade dos implantes de NT-TiO2 existentes.

Simple model of adsorption on external surface of carbon nanotubes: a new analytical approach basing on molecular simulation data

Nitrogen adsorption on carbon nanotubes is wide- ly studied because nitrogen adsorption isotherm measurement is a standard method applied for porosity characterization. A further reason is that carbon nanotubes are potential adsorbents for separation of nitrogen from oxygen in air. The study presented here describes the results of GCMC simulations of nitrogen (three site model) adsorption on single and multi walled closed nanotubes. The results obtained are described by a new adsorption isotherm model proposed in this study. The model can be treated as the tube analogue of the GAB isotherm taking into account the lateral adsorbate-adsorbate interactions. We show that the model describes the simulated data satisfactorily. Next this new approach is applied for a description of experimental data measured on different commercially available (and characterized using HRTEM) carbon nanotubes. We show that generally a quite good fit is observed and therefore it is suggested that the observed mechanism of adsorption in the studied materials is mainly determined by adsorption on tubes separated at large distances, so the tubes behave almost independently.

Ultrathin graphitic structures and carbon nanotubes in a purified synthetic graphite

A new class of carbon structure is reported, which consists of microscale graphitic shells bounded by curved and faceted planes containing two to five layers. These structures were originally found in a commercial graphite produced by the Acheson process, followed by a purification treatment. The particles, which could be several hundreds of nanometres in size, were frequently decorated with nanoscale carbon particles, or short nanotubes. In some cases, nanotubes were found to be seamlessly connected to the thin shells, indicating that the formation of the shells and that of the nanotubes are intimately connected. The structures are believed to form during a purification process which involves passing an electric current through the graphite in the presence of a reactive gas. In support of this, it is shown that similar particles can be produced in a standard carbon arc apparatus. With their extremely thin graphene walls and high surface areas, the new structures may have a range of useful properties.

Adsorption from aqueous solutions on opened carbon nanotubes: organic compounds speed up delivery of water from inside

We report the results of first systematic studies of organic adsorption from aqueous solutions onto relatively long single walled carbon nanotubes (four tubes, in initial and oxidised forms). Using molecular dynamics simulations (GROMACS package) we discuss the behaviour of tube-water as well as tube-adsorbate systems, for three different adsorbates (benzene, phenol and paracetamol).

Parallel pipelined array architectures for real-time histogram computation in consumer devices

The real-time parallel computation of histograms using an array of pipelined cells is proposed and prototyped in this paper with application to consumer imaging products. The array operates in two modes: histogram computation and histogram reading. The proposed parallel computation method does not use any memory blocks. The resulting histogram bins can be stored into an external memory block in a pipelined fashion for subsequent reading or streaming of the results. The array of cells can be tuned to accommodate the required data path width in a VLSI image processing engine as present in many imaging consumer devices. Synthesis of the architectures presented in this paper in FPGA are shown to compute the real-time histogram of images streamed at over 36 megapixels at 30 frames/s by processing in parallel 1, 2 or 4 pixels per clock cycle.

Dispersion of a point-source release of a passive scalar through an urban-like array for different wind directions

The dispersion of a point-source release of a passive scalar in a regular array of cubical, urban-like, obstacles is investigated by means of direct numerical simulations. The simulations are conducted under conditions of neutral stability and fully rough turbulent flow, at a roughness Reynolds number of Reτ = 500. The Navier–Stokes and scalar equations are integrated assuming a constant rate release from a point source close to the ground within the array. We focus on short-range dispersion, when most of the material is still within the building canopy. Mean and fluctuating concentrations are computed for three different pressure gradient directions (0◦ , 30◦ , 45◦). The results agree well with available experimental data measured in a water channel for a flow angle of 0◦ . Profiles of mean concentration and the three-dimensional structure of the dispersion pattern are compared for the different forcing angles. A number of processes affecting the plume structure are identified and discussed, including: (i) advection or channelling of scalar down ‘streets’, (ii) lateral dispersion by turbulent fluctuations and topological dispersion induced by dividing streamlines around buildings, (iii) skewing of the plume due to flow turning with height, (iv) detrainment by turbulent dispersion or mean recirculation, (v) entrainment and release of scalar in building wakes, giving rise to ‘secondary sources’, (vi) plume meandering due to unsteady turbulent fluctuations. Finally, results on relative concentration fluctuations are presented and compared with the literature for point source dispersion over flat terrain and urban arrays. Keywords Direct numerical simulation · Dispersion modelling · Urban array

Fibrils and nanotubes assembled from a modified amyloid-β peptide fragment differ in the packing of the same β-sheet building blocks

The peptide AAKLVFF assembles into fibrils in water and nanotubes in methanol. Solid-state NMR data are consistent with fibrils constructed from β-sheet bilayers and nanotubes bounded by a wall of offset β-sheet monolayers. Remarkably distinct morphologies are thus traced to subtle differences in the arrangement of the same fundamental building blocks.

Synthesis and incorporation into cyclic peptides of tolan amino acids and their hydrogenated congeners: construction of an array of A–B-loop mimetics of the Cε3 domain of human IgE

The disruption of the human immunolobulin E–high affinity receptor I (IgE–FcεRI) protein–protein interaction (PPI) is a validated strategy for the development of anti asthma therapeutics. Here, we describe the synthesis of an array of conformationally constrained cyclic peptides based on an epitope of the A–B loop within the Cε3 domain of IgE. The peptides contain various tolan (i.e., 1,2-biarylethyne) amino acids and their fully and partially hydrogenated congeners as conformational constraints. Modest antagonist activity (IC50 660 μM) is displayed by the peptide containing a 2,2′-tolan, which is the one predicted by molecular modeling to best mimic the conformation of the native A–B loop epitope in IgE.