Molecular absorption spectrophotometric method for the determination of phosphorus in biodiesel

A molecular absorption method is proposed for the determination of phosphorus in biodiesel. The samples are mineralized using an ashing procedure at 550 °C followed by dissolution of the residue. The analytical procedure is based on the formation of a blue molybdenum complex. 1-amino-2-naphthol-4-sulfonic acid is used as reducing agent. The method was applied to biodiesel samples prepared from soy, canola and sunflower oils and from bovine fat. The limit of detection is 0.57 mg P kg⁻¹ and the limit of quantification is 1.7 mg P kg⁻¹. The observed mean relative standard deviation is about 5%. The simplicity of the procedure added to its precision, accuracy and low cost suggest that it is an excellent option for the determination of phosphorus in biodiesel.     

Synthesis,characterization and evaluation of phosphorylated resins in the removal of Pb<Superscript>2+</Superscript> from aqueous solutions

Phosphinic-derivative poly(styrene-co-divinylbenzene)-based on PS–DVB copolymers with different porosity degrees have been prepared by aromatic electrophilic substitution reaction using PCl₃/AlCl₃ followed by base-promoted hydrolysis. The phosphorylation reaction was analyzed by infra-red spectroscopy (FTIR), scanning electron microscopy (SEM), and thermogravimetry (TG/DTG). In addition, the phosphorous content of the phosphorylated copolymers was determined by spectrophotometry using the method based on sodium molybdate reactant so that the extension of that modification could be assessed. The performance of the phosphorylated resins in the extraction of Pb²⁺ from aqueous solutions in a batch system was also evaluated. The Pb²⁺ content was determined by atomic absorption spectrometry (AAS). These materials presented excellent extraction capacity under the contact time of 30 min and pH 6.     

Ultra Low Background Cryogenic Test Facility for Far-Infrared Radiation Detectors

The next generation of far infrared radiation detectors is aimed to reach photon noise limited performance in space based observatories such as SPICA and BLISS. These detectors operate at loading powers of the astronomical signal of a few Attowatt (10^?18 W) or less, corresponding to a sensitivity expressed in noise equivalent power as low as $\mathrm{NEP} = 2\times10^{-20}\ \mbox{W}/\sqrt{\mathrm{Hz}}$ . We have developed a cryogenic test setup for microwave Kinetic Inductance Detectors (MKIDs) that aims to reach these ultra-low background levels. Stray light is stopped by using a box in a box design with a sample holder inside another closed box. Microwave signals for the MKID readout enters the outer box through custom made coax cable filters. The stray light loading per pixel is estimated to be less than 60×10^?18 W during nominal operation, a number limited by the intrinsic sensitivity of the MKIDs used to validate the system.     

An 8-b 650-MHz folding ADC

An 8-b 650-MHz folding analog-to-digital converter (ADC) with analog error correction in the comparators is presented. With an input frequency of 150 MHz, 7.8 effective bits are obtained. The ADC is implemented in a 1-μm 13-GHz triple-level interconnect bipolar process, requiring 850 mW from a single -4.5 V supply. The die size is 4.2 mm²     

A Compact Four-Quadrant Floating-Gate MOS Multiplier

A compact, four-quadrant analog CMOS multiplier featuring wide dynamic range is presented. The capacitive voltage division obtained by the use of Floating-Gate MOS (FGMOS) transistors, and an accurate wide-swing current mirror based on active bootstrapping, allow a wide input range, low harmonic distortion, and high linearity. Simulation and measurement results for a 0.8 μm CMOS prototype demonstrate the validity of the proposed approach.     

Modelling photovoltaic modules with neural networks using angle of incidence and clearness index

A neural network for modelling photovoltaic modules using angle of incidence and clearness index is proposed. Engineers require methods to estimate the output of a photovoltaic plant depending on meteorological conditions. Therefore, models for the grid inverter and the generator must be provided, and their outputs must be combined. The connection between both models is related to the maximum power point of the generator and how it is tracked by the inverter. That maximum power point under specific conditions of irradiance and module temperature is determined by the I–V curve of the module, which must be simulated under those conditions. Algebraic procedures were used to simulate the I–V curve. Recently, neural networks have been used for the same purpose. Previous methods only take into account the irradiance and the module temperature. The model proposed is based on neural networks, and it uses not only the irradiance and the module temperature but also the angle of incidence and the instantaneous clearness index as additional inputs. The normalised clearness replaces the standard clearness index because it allows the removal of the hourly trend found in this last index. This new model improves the results obtained with previous ones as it can distinguish amongst samples with the same solar irradiance and temperature values but with different angle of incidence and instantaneous clearness index. Results show that this model could be used to improve the accuracy of the tools used to forecast the output of photovoltaic plants. Copyright © 2014 John Wiley & Sons, Ltd.     

Comments on `Analysis and applications of a multiqueue cyclicservice system with feedback'

The commenter corrects and comments on a few results reported in the paper by H. Takagi (see ibid., vol.COM-35, p.248-50, Feb. 1987). In addition, it is shown how these results can be utilized to give the average message delay for token passing protocols where each network station is allowed to send a maximum of one fixed-length packet per cycle (known as chaining discipline)     

Investigation of the influence of free convection on the heat transfer of cylinders with different aspect ratios

Electrically heated cylindrical wires are used in research and industry for fluid velocity and turbulence measurements. At very low free-stream velocities (u≤0.1 m/s), hot-wire measurements are significantly influenced by buoyant convection. Below a certain Reynolds number Re* this effect degrades the accuracy of the measurements. To assess the contribution of free-convection heat transfer to the heat balance of hot-wires in cross flow, measurements under normal gravity and microgravity (µg) conditions are compared keeping all other parameters constant. Under gravity conditions, the acceleration of gravity, the hot-wire axis and the direction of the free stream are all perpendicular to each other. The microgravity experiments were carried out in the Drop-Tower Bremen in which the residual acceleration is less than 10^?5 g during a period of 4.7 s. The present investigation is concerned with a velocity range of 0≤u≤0.35 m/s corresponding to a Reynolds number range Re<0.1 in standard air. This range includes pure free convection for Re→0 and forced-convection-dominated heat transfer for Re=0.1. At intermediate Reynolds numbers both transport mechanisms must be considered.