Control of the morphology of nanostructured particles prepared by the spray drying of a nanoparticle sol

The control of the morphology of nanostructured particles prepared by the spray drying of nanoparticle sol was investigated experimentally and the results are qualitatively explained based on available theory. A theoretical analysis indicates that the structural stability of the droplet and the hydrodynamic effects during the drying process play important roles in controlling the morphology of the resulting particles. The size of the sol in the droplet, droplet size, viscosity of droplet, drying temperature, gas flow rate, and addition of surfactant are all crucial parameters that affect the morphology of particles. Experimentally, nanostructured silica particles were prepared from a nanosize silica sol under various preparation conditions. Doughnut-shaped particles can be produced when the droplet size is large, in conjunction with high temperature, high gas flow rate and in the presence of an added surfactant. Appropriate choice of the spray drying method permits control of the particle size and shape, ranging from spheres to ellipsoids as well as doughnut-shaped particles by varying the preparation conditions. The results open a new route to controlling the formation of a wide variety of nanostructured particles.     

Effect of boundary conditions on quantum-anti-dots in the presence of a magnetic field

Many people have studied the conductance properties through an array of anti-dots, especially since the observation of Weiss oscillations. In most cases, however, in which the recursive Greenźs functions are used on a spatial lattice, periodic boundary conditions are employed. In this paper, we analyse the effects of boundary conditions and magnetic field on the conductance behavior in a number of anti-dot-shaped, GaAs/AlGaAs 2DEG quantum systems. The effect of periodic boundary conditions causes a reduction in the overall conductance. The effect of changing the boundary conditions is more profound for lower numbers of anti-dots.     

Verification of a model to predict the influence of particle inertia and gravity on a decaying turbulent particle-laden flow

In an earlier publication some of the authors presented a theoretical model for the calculation of the influence of particle inertia and gravity on the turbulence in a stationary particle-laden flow. In the present publication the model is extended for application to a decaying suspension. Also a comparison is given between predictions made with the model and experimental data (own data and data reported in the literature) on a decaying turbulent flow with particles in a water tunnel or in a wind tunnel. For most of the experiments a prediction with reasonable accuracy and an interpretation is possible by means of the model.     

Modified high-performance liquid chromatographic method for the determination of ganciclovir in plasma from patients with severe renal impairment.

Using the rapid and sensitive high-performance liquid chromatographic (HPLC) method previously described for the analysis of ganciclovir in plasma, we have observed an interfering peak which co-elutes with the peak of ganciclovir in plasma samples from heart-transplant patients with severe renal insufficiency. A slight modification of this method allows the separation of the two peaks. The modified HPLC method, presented in this paper, is suitable for the accurate determination of ganciclovir in plasma from patients with severe renal impairment.     

Self-scattering in Monte Carlo calculations of transient dynamic response in semiconductors

We have calculated the transient dynamic response in GaAs by a Monte Carlo approach. We find that the results are extremely sensitive to the value of Γ, the self-scattering parameter, which differs from results previously reported in the literature. However, when Г is selected so that $\text{〈Δ t 〉= 1/Г ? 〈τ〉}$, comparable results are obtained to those calculated without utilizing a self-scattering assumption.     

Hot electron transport effects in lead telluride

Velocity-electric field characteristics and evidence for travelling high field domains are reported for hot-electron conduction in single crystal epitaxial films of n-PbTe. Measurements were performed at 77 K, using nanosecond pulse techniques. Contact effects cause differences in the shape of the velocity-field curve and also possibly in the nature of high-field current instabilities. Pulsed Hall measurements reveal substantial time-dependent carrier generation and may indicate the presence of high-field domains.     

Quasiconformal homogeneity of genus zero surfaces

A Riemann surface M is said to be K-quasiconformally homogeneous if, for every two points p, q ∈ M, there exists a K-quasiconformal homeomorphism f: M→M such that f(p) = q. In this paper, we show there exists a universal constant K > 1 such that if M is a K-quasiconformally homogeneous hyperbolic genus zero surface other than ⅅ², then K ≥ K. This answers a question by Gehring and Palka [10]. Further, we show that a non-maximal hyperbolic surface of genus g ≥ 1 is not K-quasiconformally homogeneous for any finite K ≥ 1.     

Thermal degradation and fire behaviour of unsaturated polyesters filled with metallic oxides

Nano-alumina and submicron alumina trihydrate particles were incorporated into an unsaturated polyester resin at various loadings. The morphologies of composites showed that only nano-alumina was correctly dispersed. The thermal degradation behaviour of the composites was studied using thermogravimetric analysis and Py-GC/MS, while their fire behaviour was investigated using cone calorimeter and pyrolysis combustion flow microcalorimeter. Synergistic effects on thermal stability and heat release rate were observed for combinations between both submicron filler and nanofiller. The best result for fire behaviour was obtained for a global loading of 10wt% with an equal mass ratio for both kind of particles. Mass loss curves also showed increased char yield. The interest of combining particles with different sizes has been discussed as well as the role of water release, regarding activations energies of degradation processes.