We present a method for reducing the phase flicker originated by the pulsed modulation of a Liquid Crystal on Silicon (LCoS) Spatial Light Modulator (SLM). It consists in reducing the temperature of the LCoS in a controlled way, in order to increase the viscosity of the liquid crystal. By doing this, we increase the time response of the liquid crystal, and thus reduce the amplitude of phase fluctuations. We evaluate the efficacy of this method quantifying the temporal evolution of phase shift using an experiment that is insensitive to optical polarization fluctuations. Additionally, we determine the effect of the temperature reduction on the effective phase modulation capability of the LCoS. We demonstrate that a reduction of up to 80% of the flicker initial value can be achieved when the LCoS is brought to -8 °C.

Mammalian metallothioneins (MT-1 through MT-4) are a class of metal binding proteins containing two metal-thiolate clusters formed through the preferential coordination of d10 metals, Cu(I) and Zn(II), by 20 conserved cysteine residues located in two protein domains. MT metalation (homometallic or heterometallic Zn(II)/Cu(I) species) appears to be isoform specific and controlling zinc and copper concentrations to perform specific and distinct biological functions. Structural and functional relationships, and in vivo metalation studies, identified evolutionary features defining the metal-selectivity nature for MTs. Metallothionein-3 (MT-3) has been shown to possess the most pronounced Cu-thionein character forming Cu(I)-containing species more favorably than metallothionein-2 (MT-2), which possesses the strongest Zn-thionein character. In this work, we identify isoform-specific determinants which control metal binding selectivity bias in different MTs isoforms. By studying the reactivity of Zn7MT-2, Zn7MT-3 and Zn7MT-3 mutants towards Cu(II) to form Cu(I)4Zn4MTs, we have identified isoform-specific key non-coordinating residues governing folding/outer sphere control of metal selectivity bias in MTs metal clusters. By mutating selected residues and motifs in MT-3 to the corresponding MT-2 amino acids, we dissected key roles in modulating cluster dynamic and metal exchange rates, in increasing the Cu(I)-affinity in MT-3 N-terminal β-domain and/or modulating the higher stability of the Zn(II)-thiolate cluster in MT-2 β-domain. We thus engineered MT-3 variants in which the copper-thionein character is converted into a zinc-thionein. These results provide new insights into the molecular determinants governing metal selectivity in metal-thiolate clusters.

The proliferation of non-linear loads and the increasing penetration of Distributed Energy Resources (DER) in Medium-Voltage (MV) and Low-Voltage (LV) distribution grids, make it more difficult to maintain the power quality levels in residential electrical grids, especially in the case of weak grids. Most household appliances contain a conventional Power Factor Corrector (PFC) rectifier, which maximizes the load Power Factor (PF) but does not contribute to the regulation of the voltage Total Harmonic Distortion (T HDV) in residential electrical grids. This manuscript proposes a modification for PFC controllers by adapting the operation mode depending on the measured T HDV. As a result, the PFCs operate either in a low current Total Harmonic Distortion (T HDI) mode or in the conventional resistor emulator mode and contribute to the regulation of the T HDV and the P F at the distribution feeders. To prove the concept, the modification is applied to a current sensorless Non-Linear Controller (NLC) applied to a single-phase Boost rectifier. Experimental results show its performance in a PFC front-end stage operating in Continuous Conduction Mode (CCM) connected to the grid with different T HDV .

El acceso a la versión del editor puede requerir la suscripción del recurso Access to the published version may require subscription

Esta es la versión de autor de la comunicación de congreso publicada en: This is an author produced version of a paper published in: Abstract-A circuit that compensates the volt-seconds error across the inductor in current sensorless digital control for continuous conduction mode power factor correction (PFC) stage is presented. Low cost ad-hoc sigma-delta analog to digital converters (ADCs) are used to sample the PFC input and output voltage. Instead of being measured, the input current is estimated in a digital circuit to be used in the current loop. A nonlinear carrier control is implemented in the digital controller in order to obtain the power factor correction. Drive signal's delays causes differences between the digital current and the real current, producing that volt-seconds error. The control algorithm is compensated taking into account the delays. The influence of a wrong compensation is presented. Experimental results show power factor values and harmonic content within the IEC 61000-3-2 Class C standard in different operation conditions. Furthermore, the use of this PFC stage for electronics ballast to compensate the effect of the utility voltage fluctuation in HID lamps is also verified taking advantage of the digital device capabilities.

Abstract-Traditional digital PFC (Power Factor Correction) uses three sensors to measure the input and output voltages and the input current. Each sensor, especially the input current one, increases the cost of the system and generates power losses in case of resistive sensors. This paper presents a controller for boost PFC converters. It uses pre-calculated duty cycles generated offline, and applies them to the switch. In order to control the converter with non-nominal conditions, just one ADC (Analog to Digital Converter) is used, which measures the output voltage. Measuring the average and the ripple of the output voltage with this ADC, the controller takes compensation action for changes in the input voltage but also in the load of the converter. The average value is used to control the input voltage changes, whilst the ripple value is used to control load changes. These two loops present low frequency bandwidth, so the ADC and the whole system can be low cost. Finally, a comparator is used to detect the zero-crossing of the input voltage, so the pre-calculated values are synchronized with the ac mains. In this way, the converter only uses one ADC and one comparator, both with low bandwidth. Results show that high power factor and normative compliance are reached, even under non-nominal conditions.

No abstract

No abstract