The Role of Iron Oxides in Marine Phosphorus Cycling

Dissolved and particulate phase iron (Fe) and phosphorus (P) concentrations were characterized in Effingham Inlet, a fjord located on the west coast of Vancouver Island. The effect of redox conditions on Fe and P cycling was investigated through comparison of sediment and water samples taken above and below a water column redox boundary in the fjord. The data show that sharp increases in the concentration of dissolved P across the redox boundary cannot be explained solely by release of absorbed phosphorus associated with dissolution of iron oxide phases. These findings support new theories of P cycling in oceans, which suggest that redox sensitive cycling of polyphosphates by microorganisms may be a significant source of dissolved phosphorus in marine environments.Ellery Ingall - Faculty Mento

Section properties for cellular decks subjected to negative bending

Cellular decks are formed by attaching cold-formed “hat-shaped” deck sections on top of cold-formed steel sheets. The attachment is typically made using resistance spot welds spaced at a specific interval. The void left underneath the deck flutes and above the steel sheet provides a convenient means for the distribution of wiring and data cables throughout building systems. The section properties of cellular decks subjected to positive bending can be determined using the provisions of Chapter B of the 2001 AISI Specification (AISI, 2001). However, the provisions of Chapter B do not apply to cellular decks subjected to negative bending unless a specific weld spacing requirement is met. This requirement, set by Section D1.2 Spacing of Connections in Compression Elements (AISI, 2001), limits weld spacing so as to completely prevent column-like buckling between welds and provide adequate resistance to horizontal shear forces. Using section D1.2 limits weld spacing to a range of 1 in. to 2 in. for most cellular decks. It is standard industry practice to space cellular deck welds at 4 in. to 8 in. on center, exceeding the limits of Section D1.2. If the spacing limits of Section D1.2 are exceeded, the 2001 AISI Specification requires that the steel sheet be neglected when determining the section properties of cellular deck in negative bending. This is done because column-like buckling is likely to occur in the sheet when it is subjected to compression forces. Although the 2001 AISI Specification has provisions in place to account for the effects of local buckling, it has no provisions in place to account for the post column-like buckling strength of the steel sheet. However, a procedure for determining the post-buckling strength of cellular decks was developed by Luttrell and Balaji (1992), and is based on the results of 82 negative bending tests performed on six cellular deck profiles. The procedure developed by Luttrell and Balaji (1992) utilizes a dimensional reduction factor, ρm, which is used to determine the effective width of the steel sheet when column-like buckling is an issue. The factors having the greatest influence on ρm include steel sheet thickness, steel sheet yield strength, weld spacing, and the depth of the deck. Although the method correlated well with the 82 bending tests performed, a ballot containing his method was not passed by AISI. The principal reason for its rejection was 2 that the reduction factor, ρm, was dimensional, which violates an AISI directive that all equations be non-dimensional so they apply to both US Standard and SI units. The primary objective of this research was to modify the method developed by Luttrell and Balaji such that the dimensional reduction factor is non-dimensional. Using Luttrell\u27s method, section properties for 49 of the 82 cellular decks tested in negative bending were determined. Section properties were not determined for the remaining 33 ECP266 and EPC3 cellular decks due to a lack of information with regard to the deck dimensions. However, a dimensionless reduction factor was developed based on the section properties of the EP-type cellular deck. The equation used to predict the reduction factor was optimized so as to reduce the error between observed and theoretical bending strength to a minimum

Strength of arc-spot welds made in single and multiple steel sheets

The objective of this research was to establish a relationship between arc spot weld shear strength and the arc time used to form the weld. Lap shear tests were performed on both 3/4 in. and 5/8 in. nominal diameter welds. Each weld was formed in one-, two-, or four-layers of sheet steel ranging from 22 gauge (0.028 in.) to 16 gauge (.057 in.). Three distinct time series were tested for each unique weld size, thickness of sheet steel and layer configuration. The first of these series were the full-time welds. The two remaining series, 2/3-time and 1/3-time welds, had arc times equal to 2/3 and 1/3 of the average full-time weld arc time, respectively. Both weld shear strength tests and weld sectioning were performed for each series of weld. Strength tests were performed on a minimum of three specimens from every weld series. If the strength of any specimen deviated by over ten percent from the mean strength, an additional specimen was tested, helping to better understand the true behavior of the weld. Comparisons were made between the strengths of full-time, 2/3- time and 1/3-time welds. Comparisons were also made between the observed strength of each weld and the strengths calculated using the 2001 AISI Specification. Each sectioning test involved measuring and documenting the visual diameter, average diameter and effective diameter of the weld. Weld penetrations were also documented as sufficient or insufficient and any porosity was noted. A single sectioning test was performed for each full-time series, while three were performed for every 2/3- time and 1/3-time series. The data taken from the strength tests and the sectioning samples proved that welds formed using reduced arc times were considerably smaller and weaker than fulltime welds. The tests also proved that proper penetration is not dependent on the arc time, but is instead a function of the welding current and sheet steel thickness

A highly anomalous Red-winged Blackbird (Agelaius phoeniceus) song

Red-winged Blackbird (Agelaius phoeniceus) is a highly vocal species with a repertoire of similar, yet acoustically distinct songs. These songs may be altered drastically if, as a nestling, the male goes deaf or becomes acoustically isolated. In deaf Red-winged Blackbirds, these dramatic song alterations may present as songs bearing slight resemblance to the introductory phrase of their normal song. Here, we present a Red-winged Blackbird song observed in Ottawa, Ontario, Canada, that is far outside any normal variation in Red-winged Blackbird songs. Given the individual’s age and the consistency of the anomalous song, it is possible that this is a deaf bird

Suspended manufacture of biological structures

We present a novel method of extrusion-based ALM for the production of cell-laden strucutres from low viscosity polymers. The traditional planar print bed is replaced with a bed of micoparticulate fluid gel. During the extrusion process, the fluid gel is displaced whilst providing a support strucutre for the low viscosity material allowing manufacture of relatively complex geometries. The extruded structure can then be easily removed from this self-healing fluid bed. For this study, a bi-layered cell-seeded construct was produced to model the osteochondral junction. Osteochondral plugs were produced by the addition of chondrocytes and osteoblasts to 1.5%w/v gellan and 1.5%w/v gellan-5% nano-hydroxyapatite respectively. The consecutive extrusion of these two solutions into the fluid bed followed by further ionic crosslinking produced the bi-layered construct that was implant into a femoral condyle defect in vitro. Cell viability following extrusion was confirmed using calcein AM/PI live/dead staining showing excellent viability. Constructs were then sectioned, and qRT-PCR was performed, showing a native collagen phenotype across the construct with evidence of matrix markers in the cartilage-like region which were also identified using fluroescent-IHC. Constructs were also tested for their bulk relaxation properties. Addition of nano-hydroxyapatite in the bone-like region resulted in a faster, more elastic relaxation than gellan alone, something that has previously been reported to favour osteogenic differentiation. Please click Additional Files below to see the full abstract

Potential Role of Inorganic Polyphosphate in the Cycling of Phosphorus Within the Hypoxic Water Column of Effingham Inlet, British Columbia

[1] The upper basin of Effingham Inlet possesses permanently anoxic bottom waters, with a water column redox transition zone typically occurring at least 40 m above the sediment‐water interface. During our sampling campaign in April and July 2007, this redox transition zone was associated with sharp peaks in a variety of parameters, including soluble reactive phosphorus (SRP) and total particulate phosphorus (TPP). Based on sequential extraction results, TPP maxima exhibited preferential accumulation of an operationally defined class of loosely adsorbed organic phosphorus (P), which may contain a substantial fraction of polyphosphate (poly‐P). This poly‐P may furthermore be involved in the redox‐dependent remobilization of SRP. For example, direct fluorometric analysis of poly‐P content revealed that particulate inorganic poly‐P was present at concentrations ranging from 1 to 9 nM P within and several meters above the TPP maximum. Below the depth of 1% oxygen saturation, however, particulate inorganic poly‐P was undetectable

Characterisation of shock wave signatures at millimetre wavelengths from Bifrost simulations

Observations at millimetre wavelengths provide a valuable tool to study the small scale dynamics in the solar chromosphere. We evaluate the physical conditions of the atmosphere in the presence of a propagating shock wave and link that to the observable signatures in mm-wavelength radiation, providing valuable insights into the underlying physics of mm-wavelength observations. A realistic numerical simulation from the 3D radiative Magnetohydrodynamic (MHD) code Bifrost is used to interpret changes in the atmosphere caused by shock wave propagation. High-cadence (1 s) time series of brightness temperature (T$_\text{b}$) maps are calculated with the Advanced Radiative Transfer (ART) code at the wavelengths $1.309$ mm and $1.204$ mm, which represents opposite sides of spectral band~$6$ of the Atacama Large Millimeter/submillimeter Array (ALMA). An example of shock wave propagation is presented. The brightness temperatures show a strong shock wave signature with large variation in formation height between $\sim0.7$ to $1.4$ Mm. The results demonstrate that millimetre brightness temperatures efficiently track upwardly propagating shock waves in the middle chromosphere. In addition, we show that the gradient of the brightness temperature between wavelengths within ALMA band $6$ can potentially be utilised as a diagnostics tool in understanding the small-scale dynamics at the sampled layers.Comment: 16 pages, 6 figures. Accepted for publication in Philosophical Transactions A of the Royal Societ