Fish passage modelling for environmental flows: Hawkesbury‐Nepean River,NSW, Australia

Robust, objective, and repeatable approaches that define flow thresholds for fish passage across critical natural barriers such as riffles, rapids, and waterfalls are required for determining environmental flow strategies. These approaches also provide an opportunity to garner community sector backing for environmental flow releases from dams in support of tangible environmental beneficiaries—native fish. This paper outlines the results of a two‐dimensional hydraulic modelling approach to fish passage assessment for Australian bass (Percalates novemaculeata) that was used to inform the development of an environmental flow regime downstream of Warrragamba Dam, NSW, Australia. Flow rates of ≥500 MLd^?1 were found to facilitate depth‐limited upstream passage through a 20‐km river reach that contained 19 natural passage barriers to adult Australian bass up to 400–450 mm in length. Ideal passage conditions were determined at flow rates of ≥1,000 MLd^?1. Juvenile bass passage was found to be inhibited by high velocities at flow rates >250 MLd^?1, with flows of 100–250 MLd^?1 providing ideal conditions for juvenile passage. Fish length, body depth, and caudal fin depth data, as used in this study for Australian bass, provided more precise fish passage depth thresholds. Precision in fish passage assessments is important as each centimetre of additional flow depth influences cost–benefit analyses of environmental flow releases versus consumptive water uses. Although hydraulic modelling and field‐based approaches to fish passage assessment are well established, there is currently a lack of published data on native Australian freshwater fish length, body depth, and caudal fin depth data for use in fish passage assessments and for inclusion in “fish‐friendly” government policy initiatives.     

Membranes of mammary gland. XI. Marker enzyme distribution profiles for membranous components from bovine mammary gland.

Enzyme distribution profiles of clarified bovine mammary homogenates separated by equilibrium centrifugation on linear sucrose gradients suggested that several of the commonly utilized marker enzymes for rat liver are also valid markers for mammary cellular components. These marker enzymes include: Succinate dehydrogenase (mitochondria), nicotinamide adenine dinucleotide phosphate cytochrome c reductase and, to a lesser extent, retenone insensitive nicotinamide adenine dinucleotide cytochrome c reductase (endoplasmic reticulum), galactosyl transferase (Golgi apparatus), 5'-nucleotidase (plasma membranes), uric acid oxidase (microbodies), and acid phosphatase (lysosomes). Rotenone sensitive nicotinamide adenine dinucleotide cytochrome c reductase and sodium, potassium, magnesium-stimulated adenosine triphosphatase were widely distributed among subcellular fractions and are not valid marker enzymes. The boyant densities determined for the above fractions should aid in design of methods to obtain enriched sources of these components for analysis.     

Relaxation measurements of an MRI system phantom at low magnetic field strengths

Objective

Temperature controlled T₁ and T₂ relaxation times are measured on NiCl₂ and MnCl₂ solutions from the ISMRM/NIST system phantom at low magnetic field strengths of 6.5 mT, 64 mT and 550 mT.

Materials and methods

The T₁ and T₂ were measured of five samples with increasing concentrations of NiCl₂ and five samples with increasing concentrations of MnCl₂. All samples were scanned at 6.5 mT, 64 mT and 550 mT, at sample temperatures ranging from 10 °C to 37 °C.

Results

The NiCl₂ solutions showed little change in T₁ and T₂ with magnetic field strength, and both relaxation times decreased with increasing temperature. The MnCl₂ solutions showed an increase in T₁ and a decrease in T₂ with increasing magnetic field strength, and both T₁ and T₂ increased with increasing temperature.

Discussion

The low field relaxation rates of the NiCl₂ and MnCl₂ arrays in the ISMRM/NIST system phantom are investigated and compared to results from clinical field strengths of 1.5 T and 3.0 T. The measurements can be used as a benchmark for MRI system functionality and stability, especially when MRI systems are taken out of the radiology suite or laboratory and into less traditional environments.

     

In vivo quantitative MRI: T1 and T2 measurements of the human brain at 0.064 T

Objective

To measure healthy brain \({T}_{1}\) and \({T}_{2}\) relaxation times at 0.064 T.

Materials and methods

\({T}_{1}\) and \({T}_{2}\) relaxation times were measured in vivo for 10 healthy volunteers using a 0.064 T magnetic resonance imaging (MRI) system and for 10 test samples on both the MRI and a separate 0.064 T nuclear magnetic resonance (NMR) system. In vivo \({T}_{1}\) and \({T}_{2}\) values are reported for white matter (WM), gray matter (GM), and cerebrospinal fluid (CSF) for automatic segmentation regions and manual regions of interest (ROIs).

Results

\({T}_{1}\) sample measurements on the MRI system were within 10% of the NMR measurement for 9 samples, and one sample was within 11%. Eight \({T}_{2}\) sample MRI measurements were within 25% of the NMR measurement, and the two longest \({T}_{2}\) samples had more than 25% variation. Automatic segmentations generally resulted in larger \({T}_{1}\) and \({T}_{2}\) estimates than manual ROIs.

Discussion

\({T}_{1}\) and \({T}_{2}\) times for brain tissue were measured at 0.064 T. Test samples demonstrated accuracy in WM and GM ranges of values but underestimated long \({T}_{2}\) in the CSF range. This work contributes to measuring quantitative MRI properties of the human body at a range of field strengths.