Choosing the observational likelihood in state-space stock assessment models

Data used in stock assessment models result from combinations of biological, ecological, fishery, and sampling processes. Since different types of errors propagate through these processes it can be difficult to identify a particular family of distributions for modelling errors on observations a priori. By implementing several observational likelihoods, modelling both numbers- and proportions-at-age, in an age based state-space stock assessment model, we compare the model fit for each choice of likelihood along with the implications for spawning stock biomass and average fishing mortality. We propose using AIC intervals based on fitting the full observational model for comparing different observational likelihoods. Using data from four stocks, we show that the model fit is improved by modelling the correlation of observations within years. However, the best choice of observational likelihood differs for different stocks, and the choice is important for the short-term conclusions drawn from the assessment model; in particular, the choice can influence total allowable catch advise based on reference points.Comment: To be published in Canadian Journal of Fisheries and Aquatic Science

Efficient Charge Separation in 2D Janus van der Waals Structures with Build-in Electric Fields and Intrinsic p-n Doping

Janus MoSSe monolayers were recently synthesised by replacing S by Se on one side of MoS$_2$ (or vice versa for MoSe$_2$). Due to the different electronegativity of S and Se these structures carry a finite out-of-plane dipole moment. As we show here by means of density functional theory (DFT) calculations, this intrinsic dipole leads to the formation of built-in electric fields when the monolayers are stacked to form $N$-layer structures. For sufficiently thin structures ($N<4$) the dipoles add up and shift the vacuum level on the two sides of the film by $\sim N \cdot 0.7$ eV. However, for thicker films charge transfer occurs between the outermost layers forming atomically thin n- and p-doped electron gasses at the two surfaces. The doping concentration can be tuned between about $5\cdot 10^{12}$ e/cm$^{2}$ and $2\cdot 10^{13}$ e/cm$^{2}$ by varying the film thickness. The surface charges counteract the static dipoles leading to saturation of the vacuum level shift at around 2.2 eV for $N>4$. Based on band structure calculations and the Mott-Wannier exciton model, we compute the energies of intra- and interlayer excitons as a function of film thickness suggesting that the Janus multilayer films are ideally suited for achieving ultrafast charge separation over atomic length scales without chemical doping or applied electric fields. Finally, we explore a number of other potentially synthesisable 2D Janus structures with different band gaps and internal dipole moments. Our results open new opportunities for ultrathin opto-electronic components such as tunnel diodes, photo-detectors, or solar cells

Magnetoresistance and negative differential resistance in Ni/Graphene/Ni vertical heterostructures driven by finite bias voltage: A first-principles study

Using the nonequilibrium Green function formalism combined with density functional theory, we study finite-bias quantum transport in Ni/Gr_n/Ni vertical heterostructures where $n$ graphene layers are sandwiched between two semi-infinite Ni(111) electrodes. We find that recently predicted "pessimistic" magnetoresistance of 100% for $n \ge 5$ junctions at zero bias voltage $V_b \rightarrow 0$, persists up to $V_b \simeq 0.4$ V, which makes such devices promising for spin-torque-based device applications. In addition, for parallel orientations of the Ni magnetizations, the $n=5$ junction exhibits a pronounced negative differential resistance as the bias voltage is increased from $V_b=0$ V to $V_b \simeq 0.5$ V. We confirm that both of these nonequilibrium effects hold for different types of bonding of Gr on the Ni(111) surface while maintaining Bernal stacking between individual Gr layers.Comment: 6 pages, 5 figures, PDFLaTeX; Figure labels correcte

Cathode Assessment for Maximizing Current Generation in Microbial Fuel Cells Utilizing Bioethanol Effluent as Substrate

Implementation of microbial fuel cells (MFCs) for electricity production requires effective current generation from waste products via robust cathode reduction. Three cathode types using dissolved oxygen cathodes (DOCs), ferricyanide cathodes (FeCs) and air cathodes (AiCs) were therefore assessed using bioethanol effluent, containing 20.5 g/L xylose, 1.8 g/L arabinose and 2.5 g/L propionic acid. In each set-up the anode and cathode had an electrode surface area of 88 cm2, which was used for calculation of the current density. Electricity generation was evaluated by quantifying current responses to substrate loading rates and external resistance. At the lowest external resistance of 27 Ω and highest substrate loading rate of 2 g chemical oxygen demand (COD) per L·day, FeC-MFC generated highest average current density (1630 mA/m2) followed by AiC-MFC (802 mA/m2) and DOC-MFC (184 mA/m2). Electrochemical impedance spectroscopy (EIS) was used to determine the impedance of the cathodes. It was thereby confirmed that the FeC-MFC produced the highest current density with the lowest internal resistance for the cathode. However, in a setup using bioethanol effluent, the AiC-MFC was concluded to be the most sustainable option since it does not require ferricyanide. The data offer a new add-on option to the straw biorefinery by using bioethanol effluent for microbial electricity production

Magnesium isotopes as a probe of the Milky Way chemical evolution

The study of elemental abundance ratios from spectroscopy of stars has for a long time been used to investigate the structure and the chemical evolution history of the Milky Way. However, even with the ever-increasing number of stars with detailed abundances, many details about the Milky Way evolution are still not understood. While elemental abundance measurements already provide a lot of information, nucleosynthesis models predict not only bulk abundances of an element, but also its isotopic composition. When these can be measured, additional details about the nucleosynthesis can be obtained. The isotopic composition of elements in stars has only been measured for the lightest elements and even for these, observations of the highest quality are needed. In addition, detailed modeling of the line-formation in the stellar atmospheres is needed to correctly interpret the data. The purpose of this thesis is to: - Investigate the chemical evolution history of the massive, high metallicity globular cluster 47 Tucanae, by performing an extensive study of a range of elements in cool giants. - Perform the first study of Mg isotopes in this cluster, to further constrain its chemical evolution history. In addition, this work represents the first study ever of the effects of using 3D stellar atmospheric models to derive the Mg isotopic mixture. - Perform the first study of Mg isotopes in stars in the inner disk of the Milky Way and the Milky Way bulge, including stars in the globular cluster NGC 6522. - Demonstrate that this type of study is feasible for stars in the bulge, and show how the Mg isotopic ratios can be used to constrain chemical evolution models for this part of the Galaxy. The Mg isotopic ratios were successfully measured in all 21 observed stars and provided additional constraints on the chemical evolution history of 47 Tucanae. In addition, the first results for Mg isotopes with 3D stellar atmospheres gave improved fits to the MgH molecular features, compared to 1D. This also resulted in an increase of the measured fraction of 25Mg, improving the agreement with chemical evolution models. For the inner disk and the bulge, we reached a level of accuracy on the Mg isotopic ratios that will allow us to distinguish between different chemical evolution models. For the one field star in the bulge, we see an indication of more efficient star formation compared to the disk, but a larger sample of stars is needed before firm claims can be made

«Hvilke kunnskaper kreves av en kroppsøvingslærer på 1-7 trinn for å utøve god undervisningspraksis?» En kvalitativ studie av læreres profesjonskunnskaper i kroppsøving.

Bakgrunnen for studien er at kunnskapskravet som stilles til lærere i kroppsøvingsfaget, blir utydelig på grunn av et uklart kunnskapsobjekt i faget (Nyberg & Larsson, 2014). I tillegg til en usikker fremtid for faget (Kirk, 2011) bidrar til at profesjonskunnskapene som kommer til syne i faget blir interessant å undersøke, da disse vil ha konsekvenser for kunnskapsobjektet som kommer frem i faget. Hensikten med å belyse dette problemet er å få frem hvilke profesjonskunnskaper lærere i kroppsøving ser på som viktige for å utøve god undervisningspraksis. Vårt teoretiske rammeverk er Shulman (1987) sine kunnskapsbaser. Problemstillingen vår er: Hvilke kunnskaper kreves av en kroppsøvingslærer på barnetrinnet for å utøve god undervisningspraksis? Metodikken som er anvendt for å besvare problemstillingen er et kvalitativt forskningsdesign. Utvalget består syv lærere som vi intervjuet, disse underviser aktivt i kroppsøving på 1-7 trinn. Vi har anvendt tematisk analyse, slik som Braun og Clarke (2006) beskriver for å undersøke problemstillingen. Våre funn viser til fire kunnskaper som lærerne verdsetter for å utøve god praksis; (i) Klasseledelse (ii) Å jobbe på tvers av fag (iii) Å kunne mange aktiviteter (iv) Vurderingskompetanse. Vi viser igjennom studien at faget blir praktisert som et rekreasjonsfag og at kunnskapsobjektet i undervisningen er utydelig for lærere å tolke. Vi viser også at det er behov for et tydelig kunnskapsobjekt i faget. Til videre forskning kan det være fordelsmessig å ta et nøye blikk på hvordan de tverrfaglige temaene kommer frem i undervisningen. Nøkkelord: Kroppsøving, Profesjonskunnskap, Kunnskapsobjekt, 1-7 trinn, Tematisk analyse, Kvalitativt forskningsintervj

«Hvilke kunnskaper kreves av en kroppsøvingslærer på 1-7 trinn for å utøve god undervisningspraksis?» En kvalitativ studie av læreres profesjonskunnskaper i kroppsøving.

Bakgrunnen for studien er at kunnskapskravet som stilles til lærere i kroppsøvingsfaget, blir utydelig på grunn av et uklart kunnskapsobjekt i faget (Nyberg & Larsson, 2014). I tillegg til en usikker fremtid for faget (Kirk, 2011) bidrar til at profesjonskunnskapene som kommer til syne i faget blir interessant å undersøke, da disse vil ha konsekvenser for kunnskapsobjektet som kommer frem i faget. Hensikten med å belyse dette problemet er å få frem hvilke profesjonskunnskaper lærere i kroppsøving ser på som viktige for å utøve god undervisningspraksis. Vårt teoretiske rammeverk er Shulman (1987) sine kunnskapsbaser. Problemstillingen vår er: Hvilke kunnskaper kreves av en kroppsøvingslærer på barnetrinnet for å utøve god undervisningspraksis? Metodikken som er anvendt for å besvare problemstillingen er et kvalitativt forskningsdesign. Utvalget består syv lærere som vi intervjuet, disse underviser aktivt i kroppsøving på 1-7 trinn. Vi har anvendt tematisk analyse, slik som Braun og Clarke (2006) beskriver for å undersøke problemstillingen. Våre funn viser til fire kunnskaper som lærerne verdsetter for å utøve god praksis; (i) Klasseledelse (ii) Å jobbe på tvers av fag (iii) Å kunne mange aktiviteter (iv) Vurderingskompetanse. Vi viser igjennom studien at faget blir praktisert som et rekreasjonsfag og at kunnskapsobjektet i undervisningen er utydelig for lærere å tolke. Vi viser også at det er behov for et tydelig kunnskapsobjekt i faget. Til videre forskning kan det være fordelsmessig å ta et nøye blikk på hvordan de tverrfaglige temaene kommer frem i undervisningen. Nøkkelord: Kroppsøving, Profesjonskunnskap, Kunnskapsobjekt, 1-7 trinn, Tematisk analyse, Kvalitativt forskningsintervj