Chalcogenide microsphere fabricated from fibre taper-drawn using resistive heating

Over the last decade extreme interest for microsphere resonators has increased rapidly due to their very high quality Q factors, the ease with which they can be manufactured and their versatility in terms of materials and dopants for plenty of passive and active devices. Furthermore, microsphere resonators have the potential to add significant functionality to planar lightwave circuits when coupled to waveguides where they can provide wavelength filtering, delay and low-power switching, and laser functions [1].Recently, chalcogenides are rapidly establishing themselves technologically superior materials for emerging application in non-volatile memory and high speed switching [2] and have been considered for a range of other optoelectronic technologies. Chalcogenide glasses offer a wide wealth of active properties, an exceptionally high nonlinearity, photosensitivity, the ability to be doped with active elements including lanthanides and transitional metals and are able to form detectors, lasers and amplifiers and offer semiconductor, optical, acousto-optic, superconducting and opto-mechanical properties. Unlike any other optical material, they have been formed in to a multitude of form: such as optical fibres, thin films, bulk optical components, microsphere resonators, metamaterials and nanoparticles, patterned by CMOS compatible processing at the sub micron scale. To date, most studies on microsphere resonators have utilized silica microspheres fabricated by melting the tip of an optical fibre with the resulting stem attached to the microsphere used as a tool to place the sphere in the required location while characterizing the microsphere. In this paper high quality chalcogenide (As2S3) microspheres with diameters down to 74 µm are directly fabricated from the taper-drawn using a resistive heating process. A reasonable high quality factor greater than 105 near the wavelength of 1550 nm is demonstrated with an efficient coupling using a fibre taper with a diameter of 2 µm

High-Q bismuth silicate nonlinear glass microsphere resonators

The fabrication and characterization of a bismuth-silicate glass microsphere resonator has been demonstrated. At wavelengths near 1550 nm, high-modes can be efficiently excited in a 179 µm diameter bismuth-silicate glass microsphere via evanescent coupling using a tapered silica fiber with a waist diameter of circa 2 µm. Resonances with Q-factors as high as were observed. The dependence of the spectral response on variations in the input power level was studied in detail to gain an insight into power-dependent thermal resonance shifts. Because of their high nonlinearity and high- factors, bismuth-silicate glass microspheres offer the potential for robustly assembled fully integrated all-optical switching devices

Creep, Strength and Moisture Absorption of Adhesive Bonded FRP Joints

The effects of the environment on adhesive bonded single lap joints formed using XMC-3 and SMC-R50 composites were investigated. Tests were performed at temperatures of 23C and 93C with test coupons immersed in air, water, and 5% NaCl water mixture. The weight changes of both bonded joints (XMC-3 to SMC-R50 and SMC-R50 to SMC-R50) and unbonded materials were measured. Data were also ob tained showing the effects of moisture, temperature, and applied load on changes in weight, on creep deformation, lap shear strength, and separation modes of the joints.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68649/2/10.1177_073168448500400206.pd

Process intensification of BaSO4 nanoparticle preparation with agitation of microbubbles

AbstractThis study presents a novel technique for the controllable preparation of BaSO4 nanoparticles via the introduction of microbubbles into the reaction system. A high-concentration system based on barite industry was used, with saturated aqueous Na2SO4 and BaS solutions as the reactants. Microbubbles were generated by a membrane dispersion microreactor. The mixing performance was characterized using parallel competing reactions. The effects of various operation parameters on the nanoparticles were determined, and the reaction conditions were optimized. The results showed that the mixing performance could be improved by introducing microbubbles. The BaSO4 nanoparticles were controllably prepared, with a relatively narrow size distribution. The average particle size could likewise be reduced to approximately 40nm. A dimensionless micromixing scale of the microbubble flow was defined, and a model for predicting the BaSO4 particle size was proposed. The calculated results were consistent with the experimental data

Reduced Temperature Production of Recombinant Proteins to Increase Productivity in Mammalian Cell Culture

The production of recombinant proteins from an industrial perspective has one of its main goals is to increase the product concentration whether in batch, fed-batch or continuous perfusion bioreactor systems. However, a major problem trying to achieve high product concentration over prolonged cultivation is the loss of cell viability leading to reduced production rate and lower product quality. One possible means to achieve high product concentration and main high cell viability is to perform the bioreactor operations at a reduced temperature than that traditional used for mammalian cell cultivation. A collaborative research project between MIT and the Bioprocessing Technology Institute (BTI) was established where the MIT Ph.D. candidate (S.R. Fox) performed his research in Singapore with the assistances of BTI personnel. The goal of this project was the production of recombinant gamma interferon (γ -IFN) in Chinese Hamster Ovary (CHO) cells by operating the bioreactor at 32°C in contrast to cultivating the CHO cells at the traditional temperature of 37°C. By reducing the cultivation temperature to 32°C, we have found that the specific γ -IFN productivity can be increased to 400% as compared to the higher temperature (37°). This increase was the result of two factors. First the cell death was reduced at the lower temperature and second, the mRNA for the γ -IFN gene was greater (presumably through decreased mRNA degradation). However, at the reduced temperature, the cell’s specific growth was also impaired. Mutation and selection for higher growth rate strain at the reduced temperature was successful but we are concerned with the genetic stability of such mutants. Therefore a new collaborative project has been initiated using molecular genetics to engineer new CHO strains with higher growth rate at the reduced temperatures. The preliminary findings from this new project will be presented as a poster in this Symposium by Mr. Hong Kiat Tan.Singapore-MIT Alliance (SMA

CIRP Expression on Growth and Productivity of CHO Cells

Mammalian cell culture is typically operated at the physiological temperature of 37°C. Low temperature cell culture at 30-33°C, in particular for CHO cells, increased the specific productivity of many recombinant proteins amongst many other benefits. However, the cell density is lower, thus reducing the total protein yield. Of the 17 mammalian cold-stress genes reported to be up- or down-regulated at low temperature, CIRP shows potential as a gene target for improving recombinant protein production, as its expression levels were reported to affect both growth and specific productivity. In this study, it was shown that over-expression of the cold-stress gene CIRP did not cause growth arrest in CHO cells, in contrast to previous reports. However, over-expression of CIRP successfully improved the specific productivity and total yield of a recombinant interferon-γ CHO cell-line at 37°C by 25%.Singapore-MIT Alliance (SMA

Variability in the Stability and Productivity of Transfected Genes in Chinese Hamster Ovary (CHO) cells

In the field of biologics production, productivity and stability of the transfected gene of interest are two very important attributes that dictate if a production process is viable. To further understand and improve these two traits, we would need to further our understanding of the factors affecting them. These would include integration site of the gene, gene copy number, cell phenotypic variation and cell environment. As these factors play different parts in the development process, they lead to variable productivity and stability of the transfected gene between clones, the well-known phenomenon of “clonal variation”. A study of this phenomenon and how the various factors contribute to it will thus shed light on strategies to improve productivity and stability in the production cell line. Of the four factors, the site of gene integration appears to be one of the most important. Hence, it is proposed that work is done on studying how different integration sites affect the productivity and stability of transfected genes in the development process. For the study to be more industrially relevant, it is proposed that the Chinese Hamster Ovary dhfr-deficient cell line, CHO-DG44, is used as the model system.Singapore-MIT Alliance (SMA

The Effect of Culture Temperature on Recombinant IFN-γ Production and Quality

The goal of this research project is to analyze the effect of culture temperature on the production and quality of IFN-γ produced and secreted by suspension culture CHO cells.The effect of low temperature on IFN-γ glycosylation, which is under the control of a battery of enzymes whose activities will be influenced by temperature, is unknown. Work is focused on implementing a system for accurately monitoring the glycosylation of IFN-γ and then using the system for quantifying the effect of culture temperature on glycosylation. The system consists of immunoaffinity purification of IFN-γ , followed by capillary electrophoresis for determining glycosylation macroheterogeneity and MALDI-TOF MS and HPLC for determining glycosylation microheterogeneity. Initial results suggest that glycosylation macroheterogeneity is slightly decreased (~5%) at low temperature, thereby identifying a potential quality “bottleneck” for the use of low temperature to increase IFN-γ production. Low temperature (32°C) shifts the cells towards the non-growth, G1 portion of the cell cycle. In batch culture, if cells are shifted to low temperature once a reasonably high cell density is reached, an approximately 4-fold improvement in total IFN-γ production compared to 37°C culture is achieved. Pseudo-continuous culture was used to show that IFN-γ production is statistically significantly higher at 32°C compared to 37°C even when nutrient depletion is not a concern (p < 0.5). In fed-batch bioreactor culture, cells grown at low temperature display a short period of growth followed by a prolonged stationary phase of high specific IFN-γ productivity (~4-fold higher than compared to 37°C) whereas cells at 37°C grow rapidly, reach a peak cell density and then begin to die immediately. The net result is a 2-fold increase in total IFN-γ production at low temperature. Real-time RT-PCR was used to show that the amount of IFN-γ mRNA present during the 32°C stationary production phase is approximately 4-fold higher than the amount present during the exponential growth phase of the 37°C culture. To further explore the effect of low temperature on cell RNA levels, total RNA per cell was quantified during the course of batch cultures at 32°C and 37°C. Total RNA levels were found to be approximately 50% higher at 32°C than 37°C. The kinetics of the low temperature RNA concentration profile was modeled to obtain transcription (Ks) and degradation (Kd) rate constants and these were found to be consistent with literature values. This finding suggests that temperature shift may offer a novel approach for measuring RNA kinetic parameters in any cell system that can tolerate mild temperature changes.Singapore-MIT Alliance (SMA

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.Singapore-MIT Alliance (SMA

The Analysis of SKP1 Gene Expression in Physiological Male Sterility Induced by Chemical Hybridizing Agent SQ-1 in Wheat (Triticum aestivum L.)

Physiological male sterility induced by the chemical hybridizing agent (CHA) overcomes problems of maintenance of sterile lines and restorers. However, the mechanism of sterility is unclear. The process of tapetum of CHA-treated ‘Xi’nong 2611’ at uninucleate, binucleate and trinucleate were compared with control to determine if tapetum varying differently during developmental stages. Tapetal degradation in CHA-treated ‘Xi’nong 2611’ began at late uninucleate stage, somewhat earlier than control plants. Cytological observations indicated that the gradual degradation of the tapetum in CHA-treated ‘Xi’nong 2611’ was initiated and terminated earlier than in the control. These findings implied that CHA-induced male sterility was related to abnormally early tapetal degradation. In order to indicate the role of the SKP1 gene in fertility/sterility in wheat, its expression was assessed in anthers at uninucleate, binucleate and trinucleate stages. SKP1 expression was reduced in the later developmental stages, and there was an obvious decrease from the uninucleate to trinucleate stages. Higher expression of the SKP1 gene occurred in ‘Xi’nong 2611’ compared to CHA-treated ‘Xi’nong 2611’. This implied that SKP1 gene expression was inhibited during the fertility transformation process and was related to transformation from fertility to sterility. Moreover, the results from this study suggest that SKP1 plays an essential role of conducting fertility in physiological male sterility