Introduction

Journal of Nanoparticle Research -     

Optimal Doping for Enhanced SnO2 Sensitivity and Thermal Stability

Tin oxide nanocrystals (5–10 nm) doped with silica (0–15 wt %) were made by flame‐spray‐pyrolysis direct deposition onto the sensing electrodes and in situ stabilization by rapid flame annealing. Although increased SiO₂‐doping reduced the SnO₂ crystal and grain size, its sensing performance to ethanol vapor (0.1–50 ppm) exhibited an optimum with respect to SiO₂ content. The thermal stability and morphology of SiO₂‐doped SnO₂ nanoparticles were evaluated by sintering at 200–900 °C for 4–24 h in air. At low SiO₂ content, sintering of SnO₂ was prevented only partially resulting in small sinter necks (bottlenecks) between SnO₂ primary particles (smaller than twice the Debye length). This morphology drastically enhanced the sensitivity toward the analyte by maintaining a thermally stable high surface area and fully depleted connections at the primary particle necks. This enhancement is attributed mostly to the decreasing neck size of the SnO₂ SiO₂ heterojunctions rather than the decreasing SnO₂ crystallite and grain sizes with increasing SiO₂ doping. At high SiO₂ contents, SnO₂ sintering was inhibited as its grains were separated effectively by dielectric SiO₂; this resulted in isolated SnO₂ nanocrystals with drastically reduced sensitivity, thereby effectively being insulators.     

Direct RP‐HPLC determination of underivatized amino acids with online dual UV absorbance,fluorescence, and multiple electrochemical detection

The combined use of a dual‐UV detector, a fluorimetric one and of a multiple electrochemical (EC) detector equipped with a dual electrode, consisting of a conventional size 3 mm diameter glassy carbon electrode (GCE) and of a pair of 30 μm thick carbon microfibers, is proposed for the determination of 15 amino acids, two dipeptides and creatinine. This online coupling of the above detection modes could partially replace amino acid analysis by derivatization methods, since it solves problems concerning the direct detection of selected underivatized amino acids. Additionally, it was proved that the use of multiple‐detection allows positive peak identification in a single chromatographic run, yields more information for free amino acids and solves in some cases the problem of chromatographic resolution. In order to optimize the detection conditions of the underivatized amino acids and related compounds by different detectors, their detection characteristics were determined by adequate preliminary experiments. The electro‐oxidation characteristics of the underivatized compounds of interest were determined by hydrodynamic voltammetry using a flow cell with a macrodisc GCE and by ex‐situ voltammetry using both a GCE of conventional size and a carbon fiber disk microelectrode. Important practical advantages of microfiber and microdisk electrodes with respect to macroelectrodes were demonstrated.     

Designing coarse-grain reconfigurable architectures by inlining flexibility into custom arithmetic data-paths

This paper introduces a design technique for coarse-grained reconfigurable architectures targeting digital signal processing (DSP) applications. The design procedure is analyzed in detail and an area-time-power efficient reconfigurable kernel architecture is presented. The proposed technique inlines flexibility into custom carry-save (CS) arithmetic datapaths exploiting a stable and canonical interconnection scheme. The canonical interconnection is revealed by a transformation, called uniformity transformation, imposed on the basic architectures of CS-multipliers and CS-chain-adders/subtractors. Experimental results including quantitative and qualitative comparisons with existing reconfigurable arithmetic cores and exploration results of the proposed reconfigurable architecture are provided.     

Fractional order nonlinear mixed coupled systems with coupled integro-differential boundary conditions

We study the existence and uniqueness of solutions for a class of coupled fractional differential equations involving both Riemann-Liouville and Caputo fractional derivatives, and coupled integro-differential boundary conditions. We derive the desired results with the aid of modern methods of functional analysis. An example illustrating the abstract results is also presented.     

Face localization and authentication using color and depth images.

This paper presents a complete face authentication system integrating both two-dimensional (color or intensity) and three-dimensional (3-D) range data, based on a low-cost 3-D sensor, capable of real-time acquisition of 3-D and color images. Novel algorithms are proposed that exploit depth information to achieve robust face detection and localization under conditions of background clutter, occlusion, face pose alteration, and harsh illumination. The well-known embedded hidden Markov model technique for face authentication is applied to depth maps and color images. To cope with pose and illumination variations, the enrichment of face databases with synthetically generated views is proposed. The performance of the proposed authentication scheme is tested thoroughly on two distinct face databases of significant size. Experimental results demonstrate significant gains resulting from the combined use of depth and color or intensity information.     

Scaling-up the Production of Nanosized SiO2-particles in a Double Diffusion Flame Aerosol Reactor

Synthesis of nanophase silica (SiO₂) from hexamethyldisiloxane (HMDS) oxidation in a co-flow diffusion flame reactor at atmospheric pressure is investigated focusing on high production rates of powder. A new experimental set-up is introduced, including a diffusion burner which is operated with a ring-shape double diffusion flame. Significantly high HMDS concentrations are used resulting in SiO₂ production rates of up to 130g/h. Deposition of silica powder on the burner face is eliminated by the design of a special diffusion burner and higher collection rates are achieved using a baghouse filter. The specific surface area and the product powder composition are analyzed. Carbon black coated silica particles were produced at high production rates (130g/h) at low oxygen flow rates or using a mixture of nitrogen and oxygen as oxidant. The size of the product particles was controlled in the range of 15–170nm.     

Soft- and hard-agglomerate aerosols made at high temperatures

Criteria for aerosol synthesis of soft-agglomerate, hard-agglomerate, or even nonagglomerate particles are developed on the basis of particle sintering and coalescence. Agglomerate (or aggregate) particles are held together by weak, physical van der Waals forces (soft agglomerates) or by stronger chemical or sintering bonds (hard agglomerates). Accounting for simultaneous gas phase chemical reaction, coagulation, and sintering during the formation and growth of silica (SiO2) nanoparticles by silicon tetrachloride (SiCl4) oxidation and neglecting the spread of particle size distribution, the onset of hard-agglomerate formation is identified at the end of full coalescence, while the onset of soft-agglomerate formation is identified at the end of sintering. Process conditions such as the precursor initial volume fraction, maximum temperature, residence time, and cooling rate are explored, identifying regions for the synthesis of particles with a controlled degree of agglomeration (ratio of collision to primary particle diameters).     

The Effect of Hydrolysis Temperature on Synthesis of Bimodally Nanostructured Porous Titania

Bimodally porous (2–4 and 20–100 nm) titania powders were prepared by hydrolysis of titanium tetraisopropoxide (TTIP), and the effect of hydrolysis temperature on the phase transformation and pore structure was investigated. The phase transformation was slightly retarded with increasing hydrolysis temperature, when the initial water concentration was small. The evolution of particle phase composition from amorphous to crystalline anatase and rutile was largely proportional to the calcination temperature and the initial water concentration. The pore size distribution was bimodal with fine intra-particle pores (2–4 nm in diameter) and larger inter-particle pores (20–100 nm). The intra-particle pores decreased in diameter at the hydrolysis temperature of 20°C. The specific surface area (SSA) of the dried powders ranged from 253 to 587 m²/g and the highest SSA was obtained at the hydrolysis temperature of 20°C.