Nonconventional Production of Glass Nanofibers by Laser Spinning

The production of very long glass nanofibers with lengths up to several centimeters was demonstrated using the Laser Spinning technique. It employs a laser to melt a small volume of a solid precursor material while a high‐pressure gas jet drags the molten material away. Thus, the molten material forms glass fibers as result of its viscous elongation by the drag force and rapid cooling promoted by the gas jet. High quantities of nanofibers can be quickly produced with tailored chemical compositions. Previously reported analyses of the process revealed that the dimensions and temperature of the molten volume together with its viscosity to surface tension ratio are the main factors governing the formation of the nanofibers. Therefore, the influence of the working conditions on these parameters must be understood to control the efficiency of the process. In this work, we demonstrate that the surface tension of the melt can be controlled independently of its temperature, and consequently of its viscosity, by adjusting the relative humidity of the gas jet. This outcome increases the productivity of the process and expands its capability for the synthesis of glass nanofibers from fragile melts.     

A GRASP approach for the extended car sequencing problem

This paper presents a solution procedure for a new variant of the Car Sequencing Problem (CSP) based on the GRASP metaheuristic. In this variant, called xCSP (extended CSP), the aim is to satisfy the hard constraints of the CSP while scheduling the maximum possible number of cars with specific options at specific times of the day in order to satisfy other production requirements. Additional constraint ratios are likewise considered that force at least a minimum specific number of consecutive options. An extension of the CSP is formalized in this paper and computational results are presented using available on-line instances that verify the good performance of a GRASP procedure defined for the xCSP.     

Influence of homogenisation conditions and drying method on physicochemical properties of dehydrated emulsions containing different solid components

Dehydrated o/w emulsions containing sodium caseinate and lactose (sample 1), and gelatine, sucrose and maltodextrin (DE 10) (sample 2) were used to study the influence of homogenisation conditions – homogenisation pressure (15 and 70 MPa) and number of passes (1 and 2) – and the drying method – spray‐drying vs. freeze‐drying – on physicochemical parameters, including oil microencapsulation efficiency (ME), oil droplet size in reconstituted emulsions, water activity, glass transition temperature, powder bulk density and time for emulsion reconstitution in water. Results showed that small and uniform oil droplets attained with increased homogenisation pressure were not sufficient for high oil encapsulation. The permeability of the solid wall to the extraction solvent appeared to be the dominant factor, and this may increase with homogenisation pressure. With the exception of oil droplet size in sample 1 and ME in sample 2, the drying method exerted larger changes in the physicochemical parameters studied than the homogenisation pressure. For sample 2, significant changes in the ME were not observed between the freeze‐dried and spray‐dried samples, even though a great emulsion destabilisation was observed in the reconstituted emulsion of the latter.     

Hierarchical silicalite-1 structures based on pyrolized materials

The synthesis of silicalite-1 layers on pyrolyzed wood bodies with a desired shape was studied. The synthesis procedure is based in an “in situ” hydrothermal treatment of a precursor gel in which the support is immersed. Two different calcination methods were carried out, using a flow of air or N₂ and air. Samples were characterized by means of X-ray diffraction, thermogravimetric analyses and N₂ adsorption/desorption isotherms, revealing the existence of a micro/mesoporous hierarchical silicalite-1 structure.     

Study of catalytic homogeneous electrochemical reactions with reciprocal derivative chronopotentiometry using exponential time currents at spherical electrodes: Discrimination between transient and stationary conditions

Catalytic homogeneous electrochemical reactions have been studied with reciprocal derivative chronopotentiometry (RDCP) using an exponential time current both under transient and stationary conditions. The general expressions for the chronopotentiometric potential–time and derivative curves obtained are applicable for spherical electrodes of any radius, including planar electrodes and ultramicroelectrodes as limiting cases. The use of this programmed current has the particularity that it enables to achieve a stationary state very quickly, even when the chemical rate constants are not very high and, under these conditions a simple and quantitative characterisation of catalytic processes can be carried out. Moreover, the RDCP response is always peak-shaped, even for very high homogeneous rate constants for which the stationary response in cyclic voltammetry has a sigmoid feature. The experimental verification of the theoretical predictions has been carried out by analysing the electrocatalytic reduction of the heteropolyanion PW₁₂O₄₀^3? in an aqueous sulphuric media with an excess of nitrite.     

Sensory adaptation as Kalman filtering: theory and illustration with contrast adaptation

Sensory adaptation allows biological systems to adjust to variations in the environment. A recent theoretical work postulated that the goal of adaptation is to minimize errors in the performance of particular tasks. The proposed minimization was Bayesian and required prior knowledge of the environment and of the limitations of the mechanisms processing the information. One problem with that formulation is that the environment changes in time and the theory did not specify how to know what the current state of the environment is. Here, we extend that theory to estimate optimally the environmental state from the temporal stream of responses. We show that such optimal estimation is a generalized form of Kalman filtering. An application of this new Kalman-filtering framework is worked out for retinal contrast adaptation. It is shown that this application can account for surprising features of the data. For example, it accounts for the differences in responses to increases and decreases of mean contrasts in the environment. In addition, it accounts for the two-phase decay of contrast gain when the mean contrast in the environment rises suddenly. The success of this and related theories suggest that sensory adaptation is a form of constrained biological optimization.     

Coincidence detection with dynamic synapses

Recent experimental findings show that the efficacy of transmission in cortical synapses depends on presynaptic activity. In most neural models, however, the synapses are regarded as static entities where this dependence is not included. We study the role of activity-dependent (dynamic) synapses in neuronal responses to temporal patterns of afferent activity. Our results demonstrate that, for suitably chosen threshold values, dynamic synapses are capable of coincidence detection (CD) over a much larger range of frequencies than static synapses. The phenomenon appears to be valid for an integrate-and-fire as well as a Hodgkin-Huxley neuron and various types of CD tasks.