Pigment orientation changes detected by low temperature linear dichroism spectroscopy: cold-hardening transition in phycobilisome-containing organisms

Low temperature (77K) linear dichroism spectroscopy was used to characterize pigment orientation changes accompanying the light state transition in the cyanobacterium, Synechococcus sp. pee 6301, and cold-hardening in winter rye (Secale cereale L. cv. Puma). Samples were oriented for spectroscopy using the gel squeezing method (Abdourakhmanov et aI., 1979) and brought to 77K in liquid nitrogen. The linear dichroism (LD) spectra of Synechococcus 6301 phycobilisome/thylakoid membrane fragments cross-linked in light state 1 and light state 2 with glutaraldehyde showed differences in both chlorophyll a and phycobilin orientation. A decrease in the relative amplitude of the 681nm chlorophyll a positive LD peak was observed in membrane fragments in state 2. Reorientation of the phycobilisome (PBS) during the transition to state 2 resulted in an increase in core allophycocyanin absorption parallel to the membrane, and a decrease in rod phycocyanin parallel absorption. This result supports the "spillover" and "PBS detachment" models of the light state transition in PBS-containing organisms, but not the "mobile PBS" model. A model was proposed for PBS reorientation upon transition to state 2, consisting of a tilt in the antenna complex with respect to the membrane plane. Linear dichroism spectra of PBS/thylakoid fragments from the red alga, Porphyridium cruentum, grown in green light (containing relatively more PSI) and red light (containing relatively more PSll) were compared to identify chlorophyll a absorption bands associated with each photosystem. Spectra from red light - grown samples had a larger positive LD signal on the short wavelength side of the 686nm chlorophyll a peak than those from green light - grown fragments. These results support the identification of the difference in linear dichroism seen at 681nm in Synechococcus spectra as a reorientation of PSll chromophores. Linear dichroism spectra were taken of thylakoid membranes isolated from winter rye grown at 20°C (non-hardened) and 5°C (cold-hardened). Differences were seen in the orientation of chlorophyll b relative to chlorophyll a. An increase in parallel absorption was identified at the long-wavelength chlorophyll a absorption peak, along with a decrease in parallel absorption from chlorophyll b chromophores. The same changes in relative pigment orientation were seen in the LD of isolated hardened and non-hardened light-harvesting antenna complexes (LHCII). It was concluded that orientational differences in LHCII pigments were responsible for thylakoid LD differences. Changes in pigment orientation, along with differences observed in long-wavelength absorption and in the overall magnitude of LD in hardened and non-hardened complexes, could be explained by the higher LHCII monomer:oligomer ratio in hardened rye (Huner et ai., 1987) if differences in this ratio affect differential light scattering properties, or fluctuation of chromophore orientation in the isolated LHCII sample.

A Novel Accelerator Combination for the Low Temperature Curing of Silica-Filled NBR Compounds

Zinc salts of ethyl, isopropyl, and butyl xanthates were prepared in the laboratory. The effect of these xanthates in combination with zinc diethyldithiocarbamate (ZDC) on the vulcanization of silica-filled NBR compounds has been studied at different temperatures. The cure times of these compounds were compared with that of NBR compounds containing tetramethylthiuram disulphide/dibenzthiazyl disulphide. The rubber compounds with the xanthates and ZDC were cured at various temperatures from 60 to 150°C. The sheets were molded and properties such as tensile strength, tear strength, crosslink density, elongation at break, compression set, abrasion resistance, flex resistance, heat buildup, etc. were evaluated. The properties showed that zinc salt of xanthate/ZDC combination has a positive synergistic effect on the cure rate and mechanical properties of NBR compounds.

Low Temperature Curing of NBR for Property Improvement

Zinc salts of ethyl, isopropyl, and butyl xanthates are prepared in the laboratory, and the effect of these xanthates with zinc diethyl dithiocarbamate (ZDC) on the vulcanization of HAF-filled nitrile butadiene rubber (NBR) compounds has been studied at different temperatures. The cure times of these compounds have been compared with that of NBR compounds containing TMTD/MBTS. The rubber compounds with the three xanthate accelerators and ZDC are cured at various temperatures from 60 to 150°C. The sheets are molded and properties such as tensile strength, tear strength, cross-link density, elongation at break, compression set, abrasion resistance, flex resistance, etc. have been evaluated. The properties show that zinc salt of the xanthate/ZDC accelerator system has a positive synergistic effect on the cure rate and mechanical properties of NBR compounds.

Development of Polybutadiene (BR)-Polyethylene (LDPE) Blend Based Microcellular Soles for Low-Temperature Applications

Microcellular (MC) soles based on polybutadiene (BR) and low-density polyethylene (LDPE) blends for low-temperature applications were developed. A part of BR in BR-LDPE blend was replaced by natural rubber (NR) for property improvement. The BR-NR-LDPE blend-based MC sole shows good technical properties. Sulphur curing and DCP curing were tried in BR-LDPE and NR-BR-LDPE blends. Study shows that sulphur-cured MC sheets possess better technical properties than DCPcured MC sheets. 90/10 BR-LDPE and 60/30/10 BR-NR-LDPE blend combinations are found to be suitable for low-temperature applications.

Xanthate Accelerators for Low Temperature Curing of Natural Rubber

ABSTRACT: Zinc salts of ethyl, isopropyl, and butyl xanthates were prepared in the laboratory. They were purified by reprecipitation and were characterized by IR, NMR, and thermogravimetric analysis techniques. The melting points were also determined. The rubber compounds with different xanthate accelerators were cured at temperatures from 30 to 150°C. The sheets were molded and properties such as tensile strength, tear strength, crosslink density, elongation at break, and modulus at 300% elongation were evaluated. The properties showed that all three xanthate accelerators are effective for room temperature curing.

Characterization of Hydrothermally Annealed Low Temperature Bioactive Thin Film Coatings of Hydroxyapatite on TiAl6V4 Implant material

This thesis summarizes the results on the growth and characterisation of thin films of HA grown on TiAl6V4 (Ti) implant material at a lower substrate temperature by a combination of Pulsed laser deposition and a hydrothermal treatment to get sufficiently strong crystalline films suitable for orthopaedic applications. The comparison of the properties of the coated substrate has been made with other surface modification techniques like anodization and chemical etching. The in-vitro study has been conducted on the surface modified implants to assess its cell viability. A molecular level study has been conducted to analyze the adhesion mechanism of protein adhesion molecules on to HA coated implants.

Magnetic field effect on quantum corrections to the low-temperature conductivity in mettalic perovskite oxides

The transport and magnetotransport properties of the metallic and ferromagnetic SrRuO3 (SRO) and the metallic and paramagnetic LaNiO3 (LNO) epitaxial thin films have been investigated in fields up to 55 T at temperatures down to 1.8 K . At low temperatures both samples display a well-defined resistivity minimum. We argue that this behavior is due to the increasing relevance of quantum corrections to the conductivity (QCC) as temperature is lowered; this effect being particularly relevant in these oxides due to their short mean free path. However, it is not straightforward to discriminate between contributions of weak localization and renormalization of electron-electron interactions to the QCC through temperature dependence alone. We have taken advantage of the distinct effect of a magnetic field on both mechanisms to demonstrate that in ferromagnetic SRO the weak-localization contribution is suppressed by the large internal field leaving only renormalized electron-electron interactions, whereas in the nonmagnetic LNO thin films the weak-localization term is relevant.

Giant heat dissipation at the low temperature reversible-irreversible transition in Gd5Ge4

The heat exchanged at the low-temperature first-order magnetostructural transition is directly measured in Gd5Ge4 . Results show that the origin and the temperature dependence of the heat exchanged varies with the reversible/irreversible character of the first-order transition. In the reversible regime, the heat exchanged by the sample is mostly due to the latent heat at the transition and decreases with decreasing temperature, while in the irreversible regime, the heat is irreversibly dissipated and increases strongly with decreasing temperature, reaching a value of 237 J/kg at 4 K.

New accelerator system for low temperature curing of elastomers with special reference to NR, NBR and NR/BR blends

The primary objective of this work is to develop an efficient accelerator system for low temperature vulcanization of rubbers. Although xanthates are known to act as accelerators for low temperature vulcanization, a systematic study on the mechanism of vulcanization, the mechanical properties of the vulcanizates at varying temperatures of vulcanization, cure characteristics etc are not reported. Further. xanthate based curing systems are not commonly used because of their chance for premature vulcanization during processing. The proposed study is to develop a novel accelerator system for the low temperature vulcanization of rubbers having enough processing safely. lt is also proposed to develop a method for the prevulcanisation of natural rubber latex at room temperature. As already mentioned the manufacture of rubber products at low temperature will improve its quality and appearance. Also, energy consumption can be reduced by low temperature vulcanization. in addition, low temperature vulcanization will be extremely useful in the area of repair of defective products, since subjecting finished products to high temperatures during the process of repair will adversely affect the quality of the product. Further. room temperature curing accelerator systems will find extensive applications in surface coating industries.

Low temperature Mössbauer studies on magnetic nanocomposites

Nanocomposites with magnetic components possessing nanometric dimensions, lying in the range 1–10 nm, are found to be exhibiting superior physical properties with respect to their coarser sized counterparts. Magnetic nanocomposites based on gamma iron oxide embedded in a polymer matrix have been prepared and characterized. The behaviour of these samples at low temperatures have been studied using Mössbauer spectroscopy. Mössbauer studies indicate that the composites consist of very fine particles of g-Fe2O3 of which some amount exists in the superparamagnetic phase. The cycling of the preparative conditions were found to increase the amount of g-Fe2O3 in the matrix

Experimental and CFD study on low temperature drying of loose and compressed bulks

Die Trocknung ist eines der am häufigsten verwendeten Verfahren, um die Haltbarkeit von landwirtschaftlichen Gütern zu verlängern. Von den vielen gebräuchlichen Trocknungsarten ist die Konvektionstrocknung, die Luft als Energie- und Feuchteträger verwendet, weiterhin die wichtigste. Trotz ihrer Nachteile und ihres hohen spezifischen Energieverbrauchs sind Satztrockner für die Getreide-, Kräuter- und Heutrocknung noch weit verbreitet. Ferner werden Konvektionstrockner gemeinhin zur künstlichen Trocknung eingesetzt. Diese Arbeit ist Teil eines Forschungsprojekts, welches eine sorptionsgestützte solare Trocknung von landwirtschaftlichen Gütern untersucht. Bei dieser wird kühle feuchte Luft in Kontakt mit einer konzentrierten hygroskopischen Salzlösung gebracht. Während dieses Prozesses wird die Luft entfeuchtet und mit Hilfe der freigesetzten Verdampfungsenthalpie erwärmt. Die Anwendung dieses Verfahrens zur Trocknung landwirtschaftlicher Güter ist besonders interessant für Produkte, die bei niedrigen Temperaturen verarbeitet werden, um ihre Qualität nicht negativ zu beeinflussen. Bei allen energieintensiven Prozessen und vor allem bei der Verwendung von Solarenergie ist ein effizienter Energieverbrauch äußerst wichtig für den technischen und ökonomischen Erfolg. Eine ungleichmäßige Trocknung ist oftmals bei Satztrocknern zu beobachten, was die Energieeffizienz negativ beeinflusst. Aus diesem Grund lag im agrartechnischen Teil des Projekts der Schwerpunkt auf der Trocknung bei niedrigen Temperaturen und geringer Luftfeuchte, die der Sorptionsprozess liefert, sowie auf der Verbesserung der Luftverteilung und der Gleichmäßigkeit der Trocknung in lockeren und verdichteten Schüttungen. Es wurden Dünnschicht-Trocknungsexperminente für Blattsellerie bei unterschiedlichen Lufttemperaturen und unterschiedlicher relativer Luftfeuchte durchgeführt. Die Ergebnisse zeigen eindeutig, dass nicht nur die Lufttemperatur einen großen Einfluss auf die Trocknungsgeschwindigkeit hat, sondern auch die relative Luftfeuchte. Dies ist vor allem bei niedrigen Temperaturen, wie sie vom Sorptionssystem geliefert werden, der Fall. Um die Luftverteilung und Gleichmäßigkeit der Trocknung lockerer Schüttungen zu untersuchen, wurde ein Kistentrockner experimentell und in Strömungssimulationen getestet. Die Leistung des ursprünglichen Trockners wurde signifikant durch einfache Veränderungen des Designs verbessert. Diese stellten einen gleichmäßigeren Luftstrom durch das Produkt sicher. Die Trocknung von Heu-Rundballen stellt eine Herausforderung dar, da diese sehr stark verdichtet sind und die Dichte innerhalb eines Ballens stark schwankt. Strömungs- und Trocknungssimulationen so wie experimentelle Messungen zeigten, dass das Trocknerdesign einen großen Einfluss auf die Gleichmäßigkeit der Trocknung hat. Bei den einfachsten Trocknervarianten war die Verteilung auch bei optimal gepressten Ballen unzureichend, während komplexere Trockner eine gleichmäßigere Trocknung erzielten. Jedoch werden auch hier die Ergebnisse stark von der Verteilung der Dichte im Ballen beeinflusst, welche in der Praxis weiterhin nicht ideal ist. Abschließend wurde, um den Trocknungsfortschritt zu überwachen, eine Methodik getestet, bei der zur Messung des durchschnittlichen aktuellen Feuchtegehalts des Produktes psychrometrische Messungen und Messungen des Luftstroms in kurzen Abständen durchgeführt wurden. Die Menge des tatsächlich entfernten Wassers stimmte in den meisten Fällen gut mit der geschätzten Menge überein. Jedoch hängt der Erfolg dieser Methode stark von der Genauigkeit der Messfühler ab.

Preliminary Characterisation of Low-Temperature Bonded Copper Interconnects for 3-D Integrated Circuits

Three dimensional (3-D) integrated circuits can be fabricated by bonding previously processed device layers using metal-metal bonds that also serve as layer-to-layer interconnects. Bonded copper interconnects test structures were created by thermocompression bonding and the bond toughness was measured using the four-point test. The effects of bonding temperature, physical bonding and failure mechanisms were investigated. The surface effects on copper surface due to pre-bond clean (with glacial acetic acid) were also looked into. A maximum average bond toughness of approximately 35 J/m² was obtained bonding temperature 300 C.

Cell-line Engineering of Chinese Hamster Ovary Cells for Low-temperature Culture

Developments in mammalian cell culture and recombinant technology has allowed for the production of recombinant proteins for use as human therapeutics. Mammalian cell culture is typically operated at the physiological temperature of 37°. However, recent research has shown that the use of low-temperature conditions (30-33°) as a platform for cell-culture results in changes in cell characteristics, such as increased specific productivity and extended periods of cell viability, that can potentially improve the production of recombinant proteins. Furthermore, many recent reports have focused on investigating low-temperature mammalian cell culture of Chinese hamster ovary (CHO) cells, one of the principal cell-lines used in industrial production of recombinant proteins. Exposure to low ambient temperatures exerts an external stress on all living cells, and elicits a cellular response. This cold-stress response has been observed in bacteria, plants and mammals, and is regulated at the gene level. The exact genes and molecular mechanisms involved in the cold-stress response in prokaryotes and plants have been well studied. There are also various reports that detail the modification of cold-stress genes to improve the characteristics of bacteria or plant cells at low temperatures. However, there is very limited information on mammalian cold-stress genes or the related pathways governing the mammalian cold-stress response. This project seeks to investigate and characterise cold-stress genes that are differentially expressed during low-temperature culture of CHO cells, and to relate them to the various changes in cell characteristics observed in low-temperature culture of CHO cells. The gene information can then be used to modify CHO cell-lines for improved performance in the production of recombinant proteins.

Characterisation of low temperature and semi-insulating GaAs lateral photo-Dember THz Emitters

Poster for IRMMW-THz conference in Mainz, Germany 2013