Influence of sodium dodecyl sulfate and cetyl trimethylammonium bromide upon calcium carbonate precipitation on bacterial cellulose

Calcium carbonate was deposed on bacterial cellulose (BC) never-dried membranes in the presence of different concentrations of sodium dodecyl sulfate (SDS) and cetyl trimethylammonium bromide (CTAB) by a precipitation reaction between aqueous solutions of calcium chloride (CaCl₂) and sodium carbonate (Na₂CO₃) containing, or not, surfactant in their composition. Different shapes of crystals were obtained from rhombohedral ones to flowerlike, depending on surfactant type and concentration. From the two surfactants tested, SDS has a greater influence on calcium carbonate morphology than CTAB. The only polymorph obtained in all studied cases was calcite. The composite films BC-calcite were characterized by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and color measurements. The obtained BC-calcium carbonate composites could be used in paper manufacturing.     

Direct Transcription of Two‐Dimensional Colloidal Crystal Arrays into Three‐Dimensional Photonic Crystals

A simple protocol for the fabrication of three‐dimensional (3D) photonic crystals in silicon is presented. Surface structuring by nanosphere lithography is merged with a novel silicon etching method to fabricate ordered 3D architectures. The SPRIE method, sequential passivation reactive ion etching, is a one‐step processing protocol relying on sequential passivation and reactive ion etching reactions using C₄F₈ and SF₆ plasma chemistries. The diffusion of fresh reactants and etch product species inside the etched channels is found to play an important role affecting the structural uniformity of the designed structures and the etch rate drift is corrected by adjusting the reaction times. High quality photonic crystals are thus obtained by adding the third dimension to the two‐dimensional (2D) colloidal crystal assemblies through SPRIE. Careful adjustments of both mask design and lateral etch extent balance allow the implementation of even more complex functionalities including photonic crystal slabs and precise defect engineering. 3D photonic crystal lattices exhibiting optical stop‐bands in the infrared spectral region are demonstrated, proving the potential of SPRIE for fast, simple, and large‐scale fabrication of photonic structures.     

The Estimation of Localized Corrosion Behavior of Ni-Based Dental Alloys Using Electrochemical Techniques

The aim of this study is to investigate the electrochemical behavior of the five non-precious Ni-based dental casting alloys in acidified artificial saliva. For comparison, nickel was also investigated. In order to study the localized corrosion resistance, the cyclic potentiodynamic polarization (CCP) and electrochemical impedance spectroscopy were performed. Scanning electron microscopy (SEM) observations were made after the CCP tests. The Ni-Cr alloys with chromium (14-18%) contents were susceptible to localized corrosion. The Ni-Cr-Mo alloy with contents of chromium (??13%) and molybdenum (9%) presents a dangerous breakdown, but have a zero corrosion potential so that the difference between them is around 650?mV. The Ni-Cr-Mo alloys with higher chromium (22-25%) and molybdenum (9-11%) contents had a much larger passive range in the polarization curve and were immune to pitting corrosion. Pitting resistance equivalent (PRE) of about ??54 could provide the Ni-based alloy with a good pitting corrosion resistance.     

Exergy efficiency and conversion of chemical reactions

An exergy analysis of the ammonia oxidation in nitrous oxide has been performed using alternatively the conventional second law efficiency and the more recently proposed intrinsic exergy efficiency. It is shown that the second law efficiency does not account for the conversion effect on the overall performance of a chemical system while the intrinsic exergy efficiency does. It is also shown that the results apply to any single reaction system.     

Theory of the field-assisted photomagnetoelectric effect in thin films: Experiment on n-type GaAs and applications

The field-assisted photomagnetoelectric (FAPME) effect is the generalization of the classical PME effect obtained by the application of a (strong) longitudinal electric field: photogenerated carriers are magnetoconcentrated by the Lorentz force and consequently the current-voltage (I(V)) law becomes non-linear. The theory of the FAPME effect is proposed for thin semiconductor layers, where the recombination rate at the film-substrate interface is a key parameter. The roles of other important factors (electric and magnetic fields, lifetime, dimensions) are also systematically investigated. Experimental data for the open-circuit voltage, the photomagnetoresistance and the I(V) characteristics were obtained for n-type GaAs films 1.5 μm thick in magnetic and electric fields of up to 13 T and 1.5 x 10⁴ V m^-1 respectively. A satisfactory agreement with the theory is found, in spite of some inherent limitations (film non-uniformity, influence of the semi-insulating GaAs substrate). Complementary magnetotransport measurements were performed without photoexcitation in the temperature range 77–300 K. These numerous and independent experiments are simultaneously exploited for the assessment of several basic properties of GaAs: the lifetime, the surface recombination velocities, the Hall and drift mobilities and the scattering mechanisms.     

Tunable single-mode output of a multimode laser in a tunable fibre grating external cavity

Tunable single-mode oscillation has been obtained from a 1.3?m multimode laser using a tunable fibre grating reflector in a fibre external cavity. The output was tuned over a 26 nm range with a secondary mode suppression greater than 25 dB at the centre of the gain profile.     

Hybrid modelling and constrained control of juggling systems

The goal of this article is to review the modelling framework for juggling systems by stressing the particularities of switching dynamics and to design a controller for the systems based on a reformulation of the model predictive control design. The main idea is to catch an impact during the prediction window at the desired level. One of the particularities is the on-line adaptation of the optimisation problem such that the receding prediction window assures the existence of an impact at a certain moment in absolute time. A constraints softening technique will be used to avoid the in-feasibility problems. In a first stage, the basic juggling system which consists of a ball and a juggling robot in one-dimensional case is detailed and subsequently the study is extended to the case of multiple balls juggling with two degrees of freedom. The simulation results demonstrate the performance of the presented approach.     

Explicit improved vertex control for uncertain,time‐varying linear discrete‐time systems with state and control constraints

A technique is presented to compute an explicit state feedback solution to the regulation problem for uncertain and/or time‐varying linear discrete‐time systems with state and control constraints. A piecewise affine control law is provided that not only guarantees recursive feasibility and robust asymptotic stability but is also optimal for a region of the state space containing the origin. Copyright © 2015 John Wiley & Sons, Ltd.