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Untargeted high resolution mass spectrometry approaches for identifying novel microcystins
No full textMicrocystins (MCs) are a group of hepatotoxic heptapeptides that inhibit protein phosphatases, and are produced by many species of cyanobacteria. Most MCs contain the unusual \u3b2-amino acid \u201cAdda5 \u201d, \u3b3-linked D-Glu6, and N-methyldehydroalanine (Mdha 7) at positions 5\u20137, with more than 250 different microcystin congeners having been reported in the literature, and with new congeners being discovered regularly. In addition to methods capable of measuring total MCs or targeting known congeners, improved methods are needed for identifying new candidate MCs , to ensure the safety of recreational and drinking waters. Untargeted high resolution mass spectrometry (HRMS) methods allows for simultaneous analysis of a tens of thousands of known and unknown chemicals in complex biological or environmental samples. Typically, identification of novel MCs involves only LC\u2013MS/MS analysis in positive ionization mode with detection of a characteristic fragment from Adda5 at m/z 135.0804. However, some MCs contain modified Addamoieties, or are otherwise modified to change the MS/MS conditions under which this fragment is generated, and are not readily detected in this manner. We have recently shown that thiol-derivatization of the Mdha7/Dha7 group in MCs is a highly effective method for identifying even trace amounts of novel MCs in complex matrices by LC\u2013MS. Here, we present a new approach using metabolomics software for semi-automated detection of novel MCs based on mercaptoethanol derivatization, together with accurate mass detection of precursor and characteristic product ions in negative and positive ionization modes. Taken together, this approach targets any molecules containing Adda5, D-Glu6 or Mdha7/Dha7, one or more of which is present in every microcystin reported to date. Furthermore, it is these three residues that are in closest contact with the catalytic centre of protein phosphatases, and which appear to be most important for toxicity. HRMS methods using data independent acquisition scan modes were particularly well suited for this purpose, allowing for simultaneous acquisition of MS/MS data on all compounds detected. This type of data is also well suited to retrospective analysis of newly discovered MCs from previously acquired data. The application of microcystin immunoaffinity columns containing antibodies with broad specificity to the whole family of MCs (presentation by Samdal et al.) further enhances the utility of this metabolomics workflow. We demonstrate the power of the combination of these novel approaches with the identification of numerous novel MCs in field and culture samples as well as a blue-green algal matrix reference material.Peer reviewed: YesNRC publication: Ye
Influence of substrate characteristics on single Ti splat bonding to ceramic substrates by cold spray
No full textThe cold spray technique may be used to fabricate metal matrix composites and to metallize ceramics. Both applications involve the creation of metal/ceramic interfaces, which are well researched for other processes but not nearly as much for cold spray. Here, the effect of ceramic substrate composition and surface roughness on adhesion strength of metallic splats is investigated. Splat adhesion testing was performed on Ti splats deposited on Al2O3 substrates with varying average reduced peak height roughness (Rpk) values. Ti splats sprayed onto Al2O3 with the lowest surface roughness had a higher bond strength (305\u2009\ub1\u200987 MPa) than splats deposited on the higher surface roughness Al2O3 (237\u2009\ub1\u200947 MPa). Failed interfaces revealed that the bonding mechanism for substrates with higher surface roughness is predominantly mechanical interlocking. Adhesion to the Al2O3 substrate with low surface roughness is predominantly along the periphery of the particle where jetting occurs. Splat adhesion testing was also performed on Ti splats deposited on SiC. Ti splats had a significantly higher bond strength to all Al2O3 substrates than to SiC. Posttest observations of SiC substrates showed little evidence of bonding. Several rebounded or detached splats left traces of Ti along the periphery of the impacted particle.Peer reviewed: YesNRC publication: Ye
The role of ceramic characteristics in cold sprayed metal/ceramic interfaces
No full textThe cold spray technique, historically used for metals, is increasingly being used to fabricate metal matrix composites (MMCs) and for metallization of ceramics. The quality of these materials depends on the nature of the metal/ceramic interfaces made by high speed impact. For example, the adhesion of these metal/ceramic interfaces affect the properties of MMCs, such as their wear and corrosion resistance. Here, we studied the interface of single titanium splats deposited on alumina and silicon carbide substrates. Adhesion strength is measured by a specialized splat adhesion test. The type of ceramic has a significant effect on adhesion strength and critical velocity. Surface roughness also influences adhesion and bonding mechanism in the titanium/alumina interface. Bonding on the smooth alumina substrate is associated to adiabatic shearing of the particles at impact. Bonding on the rough substrate is mainly mechanical. Interface characteristics are discussed through post-test characterization with scanning electron microscopy.Peer reviewed: NoNRC publication: Ye
The infrared imaging spectrograph (IRIS) for TMT: electronics-cable architecture
No full textThe InfraRed Imaging Spectrograph (IRIS) is a first-light instrument for the Thirty Meter Telescope (TMT). It combines a diffraction limited imager and an integral field spectrograph. This paper focuses on the electrical system of IRIS. With an instrument of the size and complexity of IRIS we face several electrical challenges. Many of the major controllers must be located directly on the cryostat to reduce cable lengths, and others require multiple bulkheads and must pass through a large cable wrap. Cooling and vibration due to the rotation of the instrument are also major challenges. We will present our selection of cables and connectors for both room temperature and cryogenic environments, packaging in the various cabinets and enclosures, and techniques for complex bulkheads including for large detectors at the cryostat wall.Peer reviewed: YesNRC publication: Ye
Design and physical model studies of innovative living breakwaters
No full textThis paper describes two separate but closely related physical models conducted to support the detailed design of the Living Breakwaters project located in Raritan Bay, New York. One study focused on optimizing and verifying the breakwater design elements to ensure they were well adapted to typical and extreme conditions, while the second study focused on verifying the overall performance of multiple living breakwaters in terms of wave attenuation and impacts on nearshore wave-induced circulation. These investigations generated a large quantity of valuable information concerning the design and performance of the breakwaters that will be used to optimize and support the final design and obtain the necessary permits required for construction.Peer reviewed: YesNRC publication: Ye
Bottom-up, robust graphene ribbon electronics in all-carbon molecular junctions
No full textLarge-area molecular electronic junctions consisting of 5-carbon wide graphene ribbons (GR) with lengths of 2\u201312 nm between carbon electrodes were fabricated by electrochemical reduction of diazotized 1,8-diaminonaphthalene. Their conductance greatly exceeds that observed for other molecular junctions of similar thicknesses, by a factor of >1
7 104 compared to polyphenylenes and >1
7 107 compared to alkane chains. The remarkable increase of conductance of the GR nanolayer results from (i) uninterrupted planarity of fused-arene structure affording extensive \u3c0-electron delocalization and (ii) enhanced electronic coupling of molecular layer with the carbon bottom contact by two-point covalent bonding, in agreement with DFT-based simulations.Peer reviewed: YesNRC publication: Ye