Interrelationships of Pacific herring, Clupea pallasi, populations and their relation to large-scale environmental and oceanographic variables

Thesis (Ph.D.) University of Alaska Fairbanks, 1999Recruitment estimates for Pacific herring, Clupea pallasi, populations in the Bering Sea and Northeast Pacific Ocean are highly variable, difficult to forecast, and crucial for determining optimum harvest levels. Age-structured population models for annual stock assessments of the sac-roe fisheries rely on fishery and survey age composition data tuned to an auxiliary survey of total biomass. In Chapter 1, the first age-structured model for Norton Sound herring was developed similarly to existing models. Estimates of variability from age-structured stock assessment models for Pacific herring are often not calculated. In Chapter 2, a parametric bootstrap procedure using a fit of the Dirichlet distribution to observed age composition data was developed as a quick and easy method for computing error estimates of model estimates. This bootstrap technique was able to capture variability beyond that of the multinomial distribution. This technique can provide estimates of variability for existing population models with age composition data requiring little change to the original model structure. Recruitment time series from Pacific herring stock assessment models for 14 populations in the Bering Sea and Northeast Pacific Ocean were analyzed for links to the environment. For some populations, recruitment series were extended backward in time using cohort analysis. In chapter 3, correlation and multivariate cluster analyses were applied to determine herring population associations. There appear to be four major herring groups: Bering Sea, outer Gulf of Alaska, coastal SE Alaska, and British Columbia. These associations were combined with an exploratory correlation analysis of environmental data in chapter 4. Appropriate time periods for environmental variables were determined for use in Ricker type environmentally dependent spawner-recruit forecasting models. Global and local scale environmental variables were examined in forecasting models, resulting in improvements in recruitment forecasts compared to models without environmental data. The exploratory correlation analysis and best fit models, determined by jackknife error prediction, indicated temperature data corresponding to the year of spawning resulted in the best forecasting models. The Norton Sound age-structured model, parametric bootstrap procedure, and recruitment forecasting models serve as enhancements to the decision process of managing Pacific herring fisheries

The influence of arsenic alloying on the localised corrosion behaviour of magnesium

An in-situ scanning vibrating electrode technique is used to investigate the effect of alloyed arsenic on magnesium immersed in chloride containing aqueous solution, both in freely corroding and anodically polarised conditions. Arsenic is shown to strongly suppress cathodic activation of the corroding Mg even under circumstances where breakdown has occurred and subsequent propagation of dark filiform-like tracks is observed. Under galvanostatic anodic polarisation, rates of hydrogen evolution are significantly mitigated compared to pure Mg and no time-dependent evolution of local cathodic sites is detected. The findings support the theory that cathodic activation of the dark corroded Mg surface is associated with accumulated transition metal impurity, which in turn become poisoned towards cathodic hydrogen evolution by the presence of As. In addition, these preliminary studies suggest that alloying with a strong cathodic poison may provide a means of producing a more-charge effective anode material for primary sea-water activated Mg batteries

Quantifying the Role of Transition Metal Plating in the Cathodic Activation of Corroding Magnesium

This paper examines the effect that transition metal ions have on the corrosion behaviour of high purity magnesium. A series of experiments indicate the ability of the selected transition metal ions to accelerate corrosion through cathodic (re)plating aiming to gain an insight on the Mg corrosion activation described in recent publications. High purity magnesium samples were used in conjunction with known additions of Fe2+, Cu2+, Zn2+ and Mn2+ cations. The results indicate that the presence of transition metal ions in the corrosive electrolyte leads to transition metal (re)plating and to an increase of the magnesium corrosion rate. By systematically varying the transition metal ion concentration it was possible to determine the relative efficiencies of the selected metal cations. It was also observed that the metal (re)plating process and the efficiency of the cathodic activation were limited by the formation of insoluble transition metal (hydr)oxide precipitates and the time-dependent hydrolysis

The influence of Chloride Ion Concentration on Passivity Breakdown in Magnesium

An empirically derived dependence of an apparent breakdown potential (Eb) of magnesium (Mg) on chloride ion concentration is reported. In situations where spontaneous breakdown in the absence of external polarization is observed, leading to the subsequent propagation of localised corrosion, Eb can be determined by following time-dependent changes in free corrosion potential (Ecorr). Breakdown of temporary passivity is marked by a clear inflection in the time-dependent value of Ecorr, characterised by a sharp decrease in potential from a maximum value where Ecorr = Eb. Characterisation of localized corrosion behaviour by in-situ scanning vibrating electrode studies, prior to and following the point of breakdown, is employed to explain the observed Ecorr vs. time characteristics. Examples of typical behaviour upon immersion in aqueous solutions containing different chloride ion concentrations ([Cl-]) are given for commercially pure Mg and an AZ31 alloy. For high purity Mg, which remains passive at pH 11 at all chloride concentrations ≤ 2 mol dm-3, Eb values are determined as a function of chloride ion concentration [Cl-] by means of a potentiodynamic method. In both cases a dependence of Eb on [Cl-] is established such that Eb = A + B log10[Cl-], where the value of B is typically -0.11 V per decade. The practical implications of the existence of a breakdown potential for Mg is considered in terms of the selection of an appropriate chloride ion concentration in standard corrosion tests

Addressing Obesity in Stevenage, Hertfordshire: A Consultation with Young People

Public Health England have identified that almost a quarter of children are overweight when they start primary school, which increases to a third when they leave in year 6 aged 10-11 years. This has implications for young peoples’ physical and mental health and also later in adult life. The newly launched NIHR Applied Research Collaboration (ARC) East of England is focusing on selected areas of health inequality and this includes neighbourhoods in Stevenage, Hertfordshire which have high rates of childhood obesity. In order to find out what young people think about these issues, Hertfordshire County Council and the University of Hertfordshire carried out a collaborative project in 2019. Hertfordshire County Council have adopted a Whole Systems approach to obesity and are keen to engage with young people in order to prioritise issues identified by them. The importance of ‘involving’ young people in shaping services has been widely documented. Two researchers met twice with 56 young people (from a range of schools) aged 16 years who were attending the National Citizen Service (NCS) scheme at a school in Stevenage in the summer holidays. A number of involvement activities were carried out during the sessions. The young people, with help from the researchers, facilitated their own informal discussion groups, using maps, flips charts, post-it notes and an anonymous suggestion box. The first session did not mention obesity but allowed open discussion about what it was like to live in Stevenage and the second session focussed more on the issue of ‘obesity and weight’. The young people were encouraged to find their own solutions and imagine if they “were in charge”. The four main themes that came from the sessions were; affordability, crime and anti-social behaviour, transport and places to go and eat. A number of solutions were suggested by the young people which included; healthy environment (e.g. cycle paths, street lights, regulation of shops), community approach (e.g. more affordable sports activities), schools (e.g. raise awareness, promote sport), focus on young people (e.g. activities for young people and healthy affordable eating outlets) and helping people maintain a healthy weight. The priorities identified by local young people and the wider issues they raised are important to take into consideration when shaping any intervention or public health initiative, especially when considering the wider determinants of health. Listening to the issues and solutions and using the language of young people is vital and young people should be included in co-designing any services that are aimed at them. Involving local young people who know an area and who can identify important issues is vital for any successful public health intervention

Smart-release inhibition of corrosion driven organic coating failure on zinc by cationic benzotriazole based pigments

A novel cationic benzotriazole pigment (CBP) based on the benzotriazolium cation (BTAH2+) exchanged into a sulfonated organic resin has been synthesized and evaluated as a means of inhibiting the corrosion-driven cathodic disbondment of organic coatings from the surface of galvanized steel. The CBP is acidic in nature (BTAH2+ pKa ≈ 1.1) and is intended to be compatible with acidic coating formulations such as etch-primers. Delamination rates, as measured using a scanning Kelvin probe (SKP), were found to decrease monotonically with increasing CBP volume fraction (ΦCBP) and to approach zero when ΦCBP = 0.1. The mechanism of CBP operation is described

An Analytic Approximation to Very High Specific Impulse and Specific Power Interplanetary Space Mission Analysis

A simple, analytic approximation is derived to calculate trip time and performance for propulsion systems of very high specific impulse (50,000 to 200,000 seconds) and very high specific power (10 to 1000 kW/kg) for human interplanetary space missions. The approach assumed field-free space, constant thrust/constant specific power, and near straight line (radial) trajectories between the planets. Closed form, one dimensional equations of motion for two-burn rendezvous and four-burn round trip missions are derived as a function of specific impulse, specific power, and propellant mass ratio. The equations are coupled to an optimizing parameter that maximizes performance and minimizes trip time. Data generated for hypothetical one-way and round trip human missions to Jupiter were found to be within 1% and 6% accuracy of integrated solutions respectively, verifying that for these systems, credible analysis does not require computationally intensive numerical techniques

The Sacrificial Protection of Steel by Zinc-Containing Sol-Gel Coatings

The scanning vibrating electrode technique (SVET), electrochemical impedance spectroscopy, and salt spray testing are used to investigate the ability of Zn rich sol-gel coatings to provide sacrificial protection to carbon steel. Three types of coatings (containing either Zn powder, a colored pigment, or both) are applied to steel. Intact coatings are shown to act as barrier layers through which electrolyte ingresses over time. Under conditions where the substrate is exposed by an artificial coating defect, SVET is used to investigate the extent to which different coatings offer sacrificial protection when the defect size is systematically changed. The total anodic current, as derived using SVET, doubles when the defect covers 25% of the total area compared to when 12% of the area is exposed. This finding is consistent with efficient sacrificial protection of the steel by the zinc based coating. This sacrificial protection is observed for up to 24 hours for cases where the defect constitutes up to 52% of total area. The protection offered in the presence of a colored pigment is delayed and it is proposed that the pigment restricts the ability of Zn to couple with the underlying steel

A Method for Quantifying the Synergistic Inhibitory Effect of Corrosion Inhibitors When Used in Combination: A ‘Chromate Generating Coating’

Corrosion inhibitive pigments, based on the cations Ce4+ and Cr3+ exchanged into smart release resins, are dispersed in a polyvinyl butyral (PVB) model coating and applied to a hot dip galvanised steel (HDG) substrate. An investigation is made into the influence of different pigment volume fractions (øpig) of Ce(IV) and Cr(III) based inhibitors, used both in isolation and combination, on the kinetics and mechanism of corrosion driven cathodic coating delamination. The rate of coating delamination is obtained using scanning Kelvin probe (SKP) potentiometry and time lapse photography, and the efficiency with which each inhibitor combination is able to resist cathodic coating delamination is calculated. Isobolograms, commonly utilized within the field of drug interaction, are presented as an effective method for characterising corrosion inhibitor interactions. In some cases, the sum of the efficiencies calculated for Ce(IV) and Cr(III) based pigments is shown to be greater than the sum of their individual efficiencies. It is proposed that Ce4+, released upon electrolyte exposure, is able to oxidize the Cr3+ species resulting in the formation of transient CrO4−2