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Determination of elevated levels of nitrate in vegetable powders by high-precision isotope dilution GC\u2013MS
No full textA high-precision isotope dilution GC\u2013MS method was employed for the determination of nitrate in processed vegetables. The samples were extracted in water, derivatized with triethyloxonium tetrafluoroborate and analyzed by headspace GC\u2013MS (15\u202fsamples/h). The method was applied to estimate the effect of drying on the content of nitrate in vegetables. The absolute amount of nitrate in a spinach sample before and after drying did not change even when the material was baked at 105\u202f\ub0C. Elevated levels of nitrate were found in commercial vegetable powders where the nitrate mass fraction exceed the percent level: 1.2\u20132.3% NO3 12 was found in spinach powders, 1.3\u20131.6% in kale powders, and 1.4% in a beetroot powder. The likely reduction of the antioxidant properties seen in vegetable powders along with their high nitrate content suggest the need to study the risk of endogenous N-nitrosation associated with these products.Peer reviewed: YesNRC publication: Ye
Investigation of gas and particle radiation modelling in wet oxy-coal combustion atmospheres
No full textIn this study, the impact of various treatments of gas and particle radiative properties on modelling radiative heat transfer in a 2D-squared enclosure with conditions representative to the post-burner region of an oxy-coal furnace with wet flue-gas recirculation is systematically investigated. The benchmark solutions for the radiative source terms and the net wall heat fluxes are computed with a narrow-band correlated-k (NBCK) model to account for the non-gray gas radiation in conjuction with the Mie-theory to compute the particle radiative properties. Comparisons with this benchmark solution show that the use of gray Henyey-Greenstein functions obtained with the Planck-mean values for the asymmetry factors of the coal/char and ash particles is sufficient to model accurately the scattering phase functions. In addition, the use of Planck-mean values for all the particle radiative properties provides predictions within 20% of the reference solutions. On the other hand, model results show that the application of a constant refractive index for ash particles induce large discrepancies, whereas such approximation can be made for coal particles without loss of accuracy. Finally, a significant amount of computational cost can be saved with no significant loss of accuracy by considering a wide-band correlated-k model instead of the NBCK model. The full-spectrum correlated-k (FSCK) scheme proposed by Modest and Riazzi (2005) based on gray scattering coefficients and phase functions improves further the computational saving with higher mean relative errors of about 5% for the radiative source terms and net wall heat fluxes. Thus, it is concluded that the FSCK model is appropriate to model the radiative heat transfer including gas and particle radiation for engineering applications.Peer reviewed: YesNRC publication: Ye
Ge-rich SiGe-based wideband polarization insensitive photonic platform for mid-infrared free-space communications
No full textThe recent advances in the development of quantum cascade laser with room temperature operation in the mid infrared paved the way for the realization of wideband communication systems. Particularly, two mid-infrared atmosphere transparency windows lying between 3-5 \u3bcm and between 8-14 \u3bcm exhibit great potential for further implementation of wideband free space communications. Additionally this wide unregulated spectral region shows reduced background noise and low Mie and Rayleigh scattering. Despite the development of a plethora of photonic components in mid infrared such as sources, detectors, passive structures, less efforts have been dedicated to investigate polarization management for information transport. In this work, the potential of Ge-rich SiGe waveguides is exploited to build a polarization insensitive platform in the mid-infrared. The gradual index evolution in SiGe alloys and geometric parameter optimization are used to obtain waveguides with birefringence below 2
710-4 and an unprecedented bandwidth in both atmosphere transparency windows i.e. near 3.5 \u3bcm and 9 \u3bcm. Following waveguide birefringence optimization an ultra-wideband and polarization insensitive multimode interference coupler was designed. The optimized structure shows a 4.5 \u3bcm wide bandwidth in transverse electric and transverse magnetic polarization at 9 \u3bcm wavelength. The developed ultra-wideband polarization insensitive photonic building blocks presented in this work pave the way for further implementation of free space communication systems in the mid infrared spectral region.Peer reviewed: YesNRC publication: Ye
Subwavelength silicon photonic metamaterials for mode multiplexing and polarization control (Conference Presentation)
No full textSubwavelength gratings (SWG) enable the synthesis of dispersion-engineered photonic metamaterials, leading to unprecedented performance in silicon photonic devices. In this work, we further explore the potential of this technology by presenting an ultra-broadband mode de/multiplexer (DE/MUX) and a polarization beamsplitter (PBS) with a novel approach for anisotropy engineering through tilted SWG structures. The proposed two-mode DE/MUX consists of a SWG-engineered multimode interference coupler (MMI), a 90\uba phase-shifter and a symmetric Y-junction. SWG structures are also included in fiber-to-chip couplers and in adiabatic transitions between Si-wire interconnect waveguides and the MMI. Simulated insertion losses of the proposed device are less than 0.18 dB in the wavelength range from 1.4 \u3bcm to 1.7 \u3bcm. These values further decrease down to 0.11 dB for the TE0 mode and 0.07 dB for the TE1 mode in the C-band wavelength range (1.53 \u2013 1.57 \u3bcm). Crosstalk of both modes is below -20.6 dB in the wavelength range from 1.4 \u3bcm to 1.7 \u3bcm and below -36 dB within the C-band. The proposed PBS consists of an MMI incorporating tilted sub-wavelength gratings. This novel anisotropy engineering technique provides independent control on the propagation constant of each polarization, enabling the implementation of shorter devices with improved performance. An extinction ratio over 20 dB and insertion losses below 1.5 dB in a 116-nm-wide bandwidth are demonstrated, for a MMI length under 100 \u3bcm.Peer reviewed: YesNRC publication: Ye
Gene expression atlas of embryo development in Arabidopsis
No full textEmbryogenesis represents a critical phase in the life cycle of flowering plants. Here, we characterize transcriptome landscapes associated with key stages of embryogenesis by combining an optimized method for the isolation of developing Arabidopsis embryos with high-throughput RNA-seq. The resulting RNA-seq datasets identify distinct overlapping patterns of gene expression, as well as temporal shifts in gene activity across embryogenesis. Network analysis revealed stage-specific and multi-stage gene expression clusters and biological functions associated with key stages of embryo development. Methylation-related gene expression was associated with early- and middle-stage embryos, initiation of photosynthesis components with the late embryogenesis stage, and storage/energy-related protein activation with late and mature embryos. These results provide a comprehensive understanding of transcriptome programming in Arabidopsis embryogenesis and identify modules of gene expression corresponding to key stages of embryo development. This dataset and analysis are a unique resource to advance functional genetic analysis of embryo development in plants.Peer reviewed: YesNRC publication: Ye
Multiphase mineral identification and quantification by laser-induced breakdown spectroscopy
No full textQuantitative mineral analysis (QMA) performed using energy-dispersive x-ray spectrometry and scanning electron microscopes (EDS-SEM) provide reliable information on the mineral abundance and texture of prepared rocks. This information helps in the optimization of the mining and milling processes, and to define the value of a deposit. Real-time analysis of coarse rock streams would greatly enhance the decision-making processes driving the mining operation efficiency; however electron-microscope-based instruments are not yet adaptable for in-field measurements. Laser-induced breakdown spectroscopy (LIBS) has been used for elemental analysis in many environments but has not been employed for true mineral quantification and identification. This work presents a new method for mineral identification and quantification using LIBS, which could be scalable to perform automated mineralogy measurement in coarse rock streams. A set of rock tiles from mining operations in Australia had QMA performed using an EDS-SEM instrument and the resulting data were used to guide and validate the results obtained by LIBS. The use of a multivariate curve resolution \u2013 alternating least square (MCR-ALS) method applied to the LIBS data allowed the identification, quantification and imaging of minerals on rock tiles, even in the presence of mixed mineral phases within the laser spot area. Mineral abundance and imaging are obtained with success for the mineral phases selected in the present work, which includes bornite, chalcopyrite, pyrite, molybdenite, quartz, chlorite, K-feldspar, albite, fluorite and calcite. The method presented a mineral quantification root mean square error below 10% for the main minerals. In addition, mineral quantification by point-counting using single laser shots per LIBS measurement is demonstrated, achieving absolute errors below 3.5% for major minerals and below 1% for minor minerals.Peer reviewed: YesNRC publication: Ye