Characterisation of a 300× photovoltaic concentrator system with one-axis tracking

A solar concentrator with one-axis tracking is being developed at our institute. This concentrator system achieves a high geometrical concentration ratio of 300 using a parabolic trough mirror and a three-dimensional second stage consisting of compound parabolic concentrators. The design of the system as well as the characterisation of the second stage is described in this paper.     

Short communication: effect of tannic acid on composition and ruminal degradability of bermudagrass and alfalfa silages

We measured the effects of the addition of tannic acid on chemical composition and crude protein (CP) ruminal degradability of bermudagrass, cv. coast cross (Cynodon dactylon L.) and alfalfa (Medicago sativa L.) silages with nylon bags incubated in the rumen of two fistulated lactating cows. Silage pH was greater for alfalfa than for bermudagrass. The addition of tannic acid had no effect on silage pH. Ammonia N was greater in alfalfa than in bermudagrass silage. Treated and control silages had similar ammonia N concentrations. The percentage of CP that was solubilized at time 0 was lower for alfalfa than for bermudagrass silage. The addition of tannic acid decreased the portion of CP solubilized at time 0 and increased the potentially degradable fraction of CP. The potentially degradable fraction of CP was greater for alfalfa than for bermudagrass. There was an interaction of species and treatment; the disappearance rate of CP increased with tannic acid treatment of alfalfa but decreased with acid treatment of bermudagrass. The effective degradability of CP was similar for control and treated alfalfa but lower for treated than for control bermudagrass. Tannic acid treatment is effective in decreasing the rapidly soluble fraction of alfalfa and bermudagrass silages, which could be beneficial to the animal because it would decrease the excess of N in the rumen after feeding. Tannic acid treatment decreased CP degradability of bermudagrass silage but had no effect on alfalfa silage, suggesting that tannic acid concentration required to effectively decrease CP degradability differs among forages.     

Electrochemical oxidation of carbon black in concentrated phosphoric acid at 135°C

The electrochemical oxidation of a high surface area carbon black (1000 m²/g) was investigated in 96% H₃PO₄ at 135°C. The total anodic current, the amount of CO₂ evolved and the oxygen content of the carbon were all measured as a function of time and potential. Two anodic processes occurred: the formation of a surface oxide and the evolution of CO₂. Both decreased with time but at different rates so that CO₂ evolution eventually became the major reaction. Various mechanisms to define the corrosion processes are discussed.     

Paracrine expression of a native soluble vascular endothelial growth factor receptor inhibits tumor growth, metastasis, and mortality rate

Vascular endothelial growth factor (VEGF) is a potent and selective vascular endothelial cell mitogen and angiogenic factor. VEGF expression is elevated in a wide variety of solid tumors and is thought to support their growth by enhancing tumor neovascularization. To block VEGF-dependent angiogenesis, tumor cells were transfected with cDNA encoding the native soluble FLT-1 (sFLT-1) truncated VEGF receptor which can function both by sequestering VEGF and, in a dominant negative fashion, by forming inactive heterodimers with membrane-spanning VEGF receptors. Transient transfection of HT-1080 human fibrosarcoma cells with a gene encoding sFLT-1 significantly inhibited their implantation and growth in the lungs of nude mice following i.v. injection and their growth as nodules from cells injected s.c. High sFLT-1 expressing stably transfected HT-1080 clones grew even slower as s.c. tumors. Finally, survival was significantly prolonged in mice injected intracranially with human glioblastoma cells stably transfected with the sflt-1 gene. The ability of sFLT-1 protein to inhibit tumor growth is presumably attributable to its paracrine inhibition of tumor angiogenesis in vivo, since it did not affect tumor cell mitogenesis in vitro. These results not only support VEGF receptors as antiangiogenic targets but also demonstrate that sflt-1 gene therapy might be a feasible approach for inhibiting tumor angiogenesis and growth.     

An efficient and flexible system for construction of adenovirus vectors with insertions or deletions in early regions 1 and 3

Human adenoviruses (Ads) are attracting considerable attention because of their potential utility for gene transfer and gene therapy, for development of live viral vectored vaccines, and for protein expression in mammalian cells. Engineering Ad vectors for these applications requires a variety of reagents in the form of Ads and bacterial plasmids containing viral DNA sequences and requires different strategies for construction of vectors for different purposes. To simplify Ad vector construction and develop a procedure with maximum flexibility, efficiency, and cloning capacity, we have developed a vector system based on use of Ad5 DNA sequences cloned in bacterial plasmids. Expanded deletions in early region 1 (3180 bp) and early region 3 (2690 or 3132 bp) can be combined in a single vector that should have a capacity for inserts of up to 8.3 kb, enough to accommodate the majority of cDNAs encoding proteins with regulatory elements. Genes can be inserted into either early region 1 or 3 or both and mutations or deletions can be readily introduced elsewhere in the viral genome. To illustrate the flexibility of the system, we have introduced a wild-type early region 3 into the vectors, and to illustrate the high capacity for inserts, we have isolated a vector with two genes totaling 7.8 kb.     

Potentiodynamic analysis of surface oxides on carbon blacks

The potentiodynamic sweep technique was applied to detect surface oxides on carbon black (Vulcan XC-72) which was subjected to heat treatment, electrochemical and chemical oxidation and gas phase oxidation. The quinone-hydroquinone redox couple was observed in the potential range 50–1280 mV (vs n.h.e.). Analysis of the current-voltage curves yielded surface concentrations of 10^?10–10^?11 moles/cm² in agreement with other techniques. The various oxidation procedures resulted in an increase in surface oxide whereas heat treatment caused a decrease.     

PREPARATION OF HOP EXTRACTS RICH IN PARTICULAR CONSTITUENTS*

When a column containing powdered hops is extracted with liquid carbon dioxide, chromatographic separation of hop components occurs. They are extracted in the order essential oils, β-acids, α-acids; and the separation is enhanced when finely milled hops are extracted. Early fractions (～0·5 hour) contain a high proportion of the available essential oils when hops are extracted at ?20°C and such extracts are suitable as a replacement for dry hops. Fractions can be obtained from extractions at ～7°C which are rich in α-acids and contain low levels of β-acids. Small amounts of fats and waxes are normally present in fractions collected towards the end of a run when seeded hops are extracted.     

Four‐junction spectral beam‐splitting photovoltaic receiver with high optical efficiency

A spectral beam‐splitting architecture is shown to provide an excellent basis for a four junction photovoltaic receiver with a virtually ideal band gap combination. Spectrally selective beam‐splitters are used to create a very efficient light trap in form of a 45° parallelepiped. The light trap distributes incident radiation onto the different solar cells with an optical efficiency of more then 90%. Highly efficient solar cells including III–V semiconductors and silicon were fabricated and mounted into the light trapping assembly. An integrated characterization of such a receiver including the measurement of quantum efficiency as well as indoor and outdoor I–V measurements is shown. Moreover, the optical loss mechanisms and the optical efficiency of the spectral beam‐splitting approach are discussed. The first experimental setup of the receiver demonstrated an outdoor efficiency of more than 34% under unconcentrated sunlight. Copyright © 2010 John Wiley & Sons, Ltd.     

Analysis of temperature coefficients for III–V multi‐junction concentrator cells

The temperature dependence of the I–V parameters of different III–V multi‐junction concentrator cells at several concentration levels was investigated. Moreover, the influence of spectral changes on the temperature coefficients of multi‐junction solar cells was examined. Complete sets of temperature coefficients of a metamorphic Ga_0.35In_0.65P/Ga_0.83In_0.17As dual‐junction cell, a metamorphic Ga_0.35In_0.65P/Ga_0.83In_0.17As/Ge triple‐junction cell and a lattice‐matched Ga_0.50In_0.50P/Ga_0.99In_0.01As/Ge triple‐junction cell determined under well‐controlled laboratory conditions are reported. Copyright © 2012 John Wiley & Sons, Ltd.     

Simulating single‐junction GaAs solar cells including photon recycling

To improve and accelerate further developments of III‐V solar cells an accurate and reliable modelling is necessary. In this work we present a comprehensive two‐ dimensional numerical model of single‐junction GaAs solar cells. Using this numerical model we achieved good correlation between measurements and simulations of single‐junction GaAs solar cells with different internal structures. We introduced the concept of optical coupling matrix in the numerical model to account for photon recycling effects. In addition, it is shown that thermionic currents have to be considered at the III‐V hetero‐interfaces. With this numerical model a powerful and flexible tool for solar cell simulation of III‐V compound semiconductor materials is now available. Copyright © 2006 John Wiley & Sons, Ltd.