Experimental demonstration of high‐concentration photovoltaics on a parabolic trough using tracking secondary optics

A new approach to high‐concentration photovoltaics (HCPV) based on a parabolic trough primary concentrator is presented. The design diverges from the standard HCPV arrangement of a two‐axis tracking point‐focus concentrator, and rather employs a simpler parabolic trough primary concentrator to reduce cost. To break the 2D limit of concentration, and bring the system into the realm of HCPV, the system employs an array of rotating secondary concentrators is arranged along the focal line of the parabolic trough. The resulting line‐to‐point (LTP) focus geometry allows the system to achieve a geometric concentration of 590×, yet still maintains the advantages of having a linear trough primary concentrator, namely manufacturability, economy, and scalability. A full‐scale prototype of the system was constructed in Biasca, Switzerland. During on‐sun tests a flux concentration of 364 suns was measured at the exit of the secondary concentrator, the highest reported concentration for any parabolic‐trough‐based system. Moreover, the system reached a peak efficiency of 20.2%, the highest measured solar‐to‐DC efficiency for a parabolic trough‐based solar collector. Long‐term performance is estimated by means of a coupled optical‐electrical model validated vis‐à‐vis the experimental results. This work serves as an experimental proof‐of‐concept for high‐concentration trough‐based collectors, thereby opening new avenues for reducing the cost of HCPV systems. Copyright © 2016 John Wiley & Sons, Ltd.     

Variation in research collaboration patterns across academic ranks

The ability to activate and manage effective collaborations is becoming an increasingly important criteria in policies on academic career advancement. The rise of such policies leads to development of indicators that permit measurement of the propensity to collaborate for academics of different ranks, and to examine the role of several variables in collaboration, first among these being the researchers’ disciplines. In this work we apply an innovative bibliometric approach based on individual propensity for collaboration to measure the differences in propensity across academic ranks, by discipline and for choice of collaboration forms—intramural, extramural domestic and international. The analysis is based on the scientific production of Italian academics for the period 2006–2010, totaling over 200,000 publications indexed in Web of Science. It shows that assistant professors register a propensity for intramural collaboration that is clearly greater than for professors of higher ranks. Vice versa, the higher ranks, but not quite so clearly, register greater propensity to collaborate at the international level.     

Coagulation bath composition and desiccation environment as tuning parameters to prepare skinless membranes via diffusion induced phase separation

Diffusion Induced Phase Separation (DIPS) is a currently used technique to produce porous membranes for a large variety of applications. A strong limitation is represented by the occurrence of a dense skin, which is formed during the process, highly reducing the membrane permeability. To overcome this issue, two modifications of the standard DIPS protocol were investigated: the use of coagulation baths composed by a solvent/nonsolvent mixture and the desiccation in a controlled environment, by modulating the partial pressure of nonsolvent vapor. An appropriate choice of coagulation bath composition, together with an appropriate desiccation protocol (i.e., the use of a nonsolvent vapor), will produce a skinless membrane, and offers the chance to control the morphology of both membrane surfaces. These results underline the importance of post‐treatment stage in membrane preparation via phase separation, thus suggesting that membrane washing/drying stage will affect the final morphology. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42151.     

Casein proteolysis in human milk: tracing the pattern of casein breakdown and the formation of potential bioactive peptides

The protein and peptide fraction of human milk samples collected from mothers of pre- and full-term infants in the first week after parturition was analysed by use of liquid chromatography-mass spectrometry and tandem mass spectrometry. By characterising the peptide sequence, we defined the pathway of casein hydrolysis which leads to the formation of small peptides through intermediate oligopeptides. It was found that the action of a plasmin-like enzyme acting on specific lysine residues is the primary step in casein degradation. This is followed by endopeptidases and/or exopeptidases mediated cleavage of the oligopeptides which, in turn, produces a multiplicity of short peptides differing by one or more amino acid residues. In this process, a series of potentially bioactive peptides (opioid, phosphopeptides) and their precursors are produced.     

Modeling of an annular photocatalytic reactor for water purification: oxidation of pesticides

Photocatalytic oxidation (PCO) over titanium dioxide (TiO2) is a "green" sustainable process for the treatment and purification of water and wastewater. However, the application of PCO for wastewater treatment on an industrial scale is currently hindered by a lack of simple mathematical models that can be readily applied to reactor design. Current models are either too simplistic or too rigorous to be useful in photocatalytic reactor design, scale-up, and optimization. In this paper a simple mathematical model is presented for slurry, annular, photocatalytic reactors that still retains the essential elements of a rigorous approach while providing simple solutions. The model extends the applicability of the thin-film model of photocatalytic reactors previously presented to include the case of geometrically thick photoreactors (i.e., those reactors in which the thickness of the annular zone is significant as compared to the outer radius of the reactor). The model uses a novel six-flux absorption-scattering model to represent the radiation field in the reaction space, which assumes that scattered photons follow the route of the six directions of the Cartesian coordinates. The model was successfully validated with experimental results from the photocatalytic oxidation of the pesticide isoproturon in an experimental reactor. The mathematical model presented may be used as a tool for the design, scale-up, and optimization of annular photocatalytic reactors for water treatment and purification.     

HCB, p,p'-DDE and PCB ontogenetic transfer and magnification in bluefin tuna (Thunnus thynnus) from the Mediterranean Sea

The bluefin tuna, Thunnus thynnus (Linnaeus 1758), is biologically and economically important in the Atlantic--Mediterranean ecosystems. Bluefin tuna feed on diverse food items depending on their age, thus they occupy different trophic levels during their lifespan. Hexachlorobenzene (HCB), p,p'-DDE and polychlorinated biphenyls (PCBs) are well-known persistent organic pollutants (POPs) in the Mediterranean basin. The relationship between stable isotopes of nitrogen (N) and the POP residue levels in tissues has recently increased knowledge on the link between the trophic levels and the contaminant accumulation. Trophic levels were estimated by using 15N/14N ratio (delta15N) and HCB, p,p'-DDE, and forty-three PCBs were quantified in bluefin tuna from the southern Tyrrhenian Sea. Results showed that changes in PCB and p,p'-DDE concentrations were a function of size and trophic level, while no correlations were observed for HCB. Apart from HCB and PCB nos. 101, 207, 95, 158, and 60 + 56, which did not show any significant increase per trophic level, the other PCBs and the p,p'-DDE increased significantly. The ontogenetic magnification factor of PCBs was 6.6 +/- 0.5, which was significantly (12 times) higher (p < 0.05) than the values found for p,p'-DDE (1.4) and HCB (1.4).     

A densification equation derived from the stress-deformation analysis of uniaxial cold compaction of metal powder mixes

A new densification equation for uniaxial cold compaction of four low alloy steel powders was determined from the deformation vs. mean axial stress correlation. Both deformation and stress are averaged along the height of the powder column. A power law relation, with two parameters representing the plasticity and the inverse of the resistance to deformation (densification) of the powder mix, respectively, fits the curves that are divided in two steps, distinguished by the prevailingdeformation/densification mechanism (rearrangement or plastic deformation).

Densification of the four powder mixes is greatly affected by the starting density in the die cavity, while the chemical composition of the base iron powder has a less significant effect.