Dependence of calibration sensitivity of a polysulfone/Ru(II)-tris(4,7-diphenyl-1,10-phenanthroline)-based oxygen optical sensor on its structural parameters

The optimum performance of an optical oxygen sensor based on polysulfone (PSF)/[Ru(II)-Tris(4,7-diphenyl-1,10-phenanthroline)] octylsulfonate (Ru(dpp)OS) was checked by carefully tuning the parameters affecting the membrane preparation. In particular, membranes having thickness ranging between 0.2 and 8.0 μm with various luminophore concentrations were prepared by dip-coating and tested. The membrane thickness was controlled by tuning the solution viscosity, and was measured both by secondary ion mass spectrometry (SIMS) and by visible spectroscopy (Vis). Luminescence-quenching-based calibration was a single value of the Stern-Volmer constant (K^′SV) for membranes containing up to 20 mmol Ru(dpp) g⁻¹ PSF (1.35 μm average thickness). The K^′SV value decreased for larger concentration. The highest sensitivity was obtained with membrane thickness around 1.6 μm, having a response time close to 1 s. Thicker membranes exhibited an emission saturation effect and were characterized by longer response time. The K^′SV behavior was interpreted on the basis of a mathematical approach accounting for the contribution of luminescence lifetime (τ₀), oxygen diffusion coefficient (DO₂) and oxygen solubility inside the membrane (sO₂) establishing the role of all of them and allowing their experimental determination. Moreover, a simple experimental way to estimate K^′SV without needing calibration was proposed. It was based either on the light emission asymmetry or on the percent variation of light emission on passing from pure nitrogen to pure oxygen.     

Low-Cost Potentiometric Sensor for Chloride Measurement in Continuous Industrial Process Control

Recently, the new updates in legislation about drinking water control and human health have increased the demand for novel electrochemical low-cost sensors, such as potentiometric ones. Nowadays, the determination of chloride ion in aqueous solutions has attracted great attention in several fields, from industrial processes to drinking water control. Indeed, chloride plays a crucial role in corrosion, also influencing the final taste of beverages, especially coffee. The main goal is to obtain devices suitable for continuous and real-time analysis. For these reasons, we investigated the possibility to develop an easy, low-cost potentiometric chloride sensor, able to perform analysis in aqueous mediums for long immersion time and reducing the need of periodic calibration. We realized a chloride ion selective electrode made of Ag/AgCl sintered pellet and we tested its response in model solutions compatible with drinking water. The sensor was able to produce a stable, reproducible, and accurate quantification of chloride in 900 s, without the need for a preliminary calibration test. This opens the route to potential applications of this sensor in continuous, in situ, and real time measurement of chloride ions in industrial processes, with a reduced need for periodic maintenance.     

Switchable photocatalysis for the chemodivergent benzylation of 4-cyanopyridines

We report a photocatalytic strategy for the chemodivergent radical benzylation of 4-cyanopyridines. The chemistry uses a single photoredox catalyst to generate benzyl radicals upon N–F bond activation of 2-alkyl N-fluorobenzamides. The judicious choice of different photocatalyst quenchers allowed us to select at will between mechanistically divergent processes. The two reaction manifolds, an ipso-substitution path proceeding via radical coupling and a Minisci-type addition, enabled selective access to regioisomeric C4 or C2 benzylated pyridines, respectively. Mechanistic investigations shed light on the origin of the chemoselectivity switch.

We report a photocatalytic strategy for the chemodivergent radical benzylation of 4-cyanopyridines. The chemistry uses a single photoredox catalyst to generate benzyl radicals upon N–F bond activation of 2-alkyl N-fluorobenzamides.     

Two-Wavelet Localization Operators on $$ L^p(\mathbb{R}^n) $$ for the Weyl-Heisenberg Group

We give results on the boundedness and compactness of localization operators with two admissible wavelets on for the Weyl-Heisenberg group.     

Entropy and irreversibility for a single isolated two level system: New individual quantum states and new nonlinear equation of motion

We propose a new nonlinear equation of motion for a single isolated two-level quantum system. The resulting generalized two-level quantum dynamical theory entails a new alternative resolution of the long-standing dilemma on the nature of entropy and irreversibility. Even for a single isolated degree of freedom, in addition to the individual mechanical states for which all the results of conventional quantum mechanics remain valid, our theory implies the existence of new nonmechanical individual quantum states. These states have nonzero individual entropy and, by virtue of a constant-energy, internal redistribution mechanism, relax irreversibly toward stable equilibrium. We discuss the possibility of an experimental verification of these conclusions by means of a high-resolution, essentially single-particle, magnetic-resonance experiment.     

Noether symmetry approach in matter-dominated cosmology with variable G and Λ

In the framework of renormalization-group improved cosmologies, we use the Noether symmetry approach to get exact and general integration of the matter-dominated cosmological equations. This is performed by using an expression of Λ = Λ (G) determined by the method itself. We also work out a comparison between such a model and the concordance ΛCDM model as to the magnitude–redshift relationship, hence showing that no appreciable differences occur.     

Smart panel with active damping units. Implementation of decentralized control

This paper contains the second part of a study on a smart panel with five decentralized velocity feedback control units using proof mass electrodynamic actuators [Gonzalez Diaz et al., J. Acoust. Soc. Am. 124, 886 (2008)]. The implementation of five decentralized control loops is analyzed, both theoretically and experimentally. The stability properties of the five decentralized control units have been assessed with the generalized Nyquist criterion by plotting the loci of the eigenvalues of the fully populated matrix of frequency response functions between the five error signals and five input signals to the amplifiers driving the actuators. The control performance properties have been assessed in terms of the spatially averaged response of the panel measured with a scanning laser vibrometer and the total sound power radiated measured in an anechoic room. The two analyses have shown that reductions of up to 10 dB in both vibration response and sound radiation are measured at low audio frequencies, below about 250 Hz.     

Diversity enabling equilibration: disorder and the ground state in artificial spin ice

We report a novel approach to the question of whether and how the ground state can be achieved in square artificial spin ices where frustration is incomplete. We identify two sources of randomness that affect the approach to ground state: quenched disorder in the island response to fields and randomness in the sequence of driving fields. Numerical simulations show that quenched disorder can lead to final states with lower energy, and randomness in the sequence of driving fields always lowers the final energy attained by the system. We use a network picture to understand these two effects: disorder in island responses creates new dynamical pathways, and a random sequence of driving fields allows more pathways to be followed.