Numerical studies of the scattering of light from a two-dimensional randomly rough interface between two dielectric media

The scattering of polarized light incident from one dielectric medium on its two-dimensional randomly rough interface with a second dielectric medium is studied. A reduced Rayleigh equation for the scattering amplitudes is derived for the case where p- or s-polarized light is incident on this interface, with no assumptions being made regarding the dielectric functions of the media. Rigorous, purely numerical, nonperturbative solutions of this equation are obtained. They are used to calculate the reflectivity and reflectance of the interface, the mean differential reflection coefficient, and the full angular distribution of the intensity of the scattered light. These results are obtained for both the case where the medium of incidence is the optically less dense medium, and in the case where it is the optically more dense medium. Optical analogues of the Yoneda peaks observed in the scattering of x-rays from metal surfaces are present in the results obtained in the latter case. Brewster scattering angles for diffuse scattering are investigated, reminiscent of the Brewster angle for flat-interface reflection, but strongly dependent on the angle of incidence. When the contribution from the transmitted field is added to that from the scattered field it is found that the results of these calculations satisfy unitarity with an error smaller than $10^{-4}$.Comment: 25 pages, 14 figure

Calculation of all elements of the Mueller matrix for scattering of light from a two-dimensional randomly rough metal surface

We calculate all the elements of the Mueller matrix, which contains all the polarization properties of light scattered from a two-dimensional randomly rough lossy metal surface. The calculations are carried out for arbitrary angles of incidence by the use of nonperturbative numerical solutions of the reduced Rayleigh equations for the scattering of p- and s-polarized light from a two-dimensional rough penetrable surface. The ability to model polarization effects in light scattering from surfaces enables better interpretation of experimental data and allows for the design of surfaces which possess useful polarization effects.Comment: 5 pages, 3 figure

A comparison of Eulerian and Lagrangian methods for vertical particle transport in the water column

A common task in oceanography is to model the vertical movement of particles such as microplastics, nanoparticles, mineral particles, gas bubbles, oil droplets, fish eggs, plankton, or algae. In some cases, the distribution of the vertical rise or settling velocities of the particles in question can span a wide range, covering several orders of magnitude, often due to a broad particle size distribution or differences in density. This requires numerical methods that are able to adequately resolve a wide and possibly multi-modal velocity distribution. Lagrangian particle methods are commonly used for these applications. A strength of such methods is that each particle can have its own rise or settling speed, which makes it easy to achieve a good representation of a continuous distribution of speeds. An alternative approach is to use Eulerian methods, where the partial differential equations describing the transport problem are solved directly with numerical methods. In Eulerian methods, different rise or settling speeds must be represented as discrete classes, and in practice, only a limited number of classes can be included. Here, we consider three different examples of applications for a water column model: positively buoyant fish eggs, a mixture of positively and negatively buoyant microplastics, and positively buoyant oil droplets being entrained by waves. For each of the three cases, we formulate a model for the vertical transport based on the advection–diffusion equation with suitable boundary conditions and, in one case, a reaction term. We give a detailed description of an Eulerian and a Lagrangian implementation of these models, and we demonstrate that they give equivalent results for selected example cases. We also pay special attention to the convergence of the model results with an increasing number of classes in the Eulerian scheme and with the number of particles in the Lagrangian scheme. For the Lagrangian scheme, we see the 1/Np convergence, as expected for a Monte Carlo method, while for the Eulerian implementation, we see a second-order (1/Nk2) convergence with the number of classes.</p

Learning from natural sediments to tackle microplastics challenges: A multidisciplinary perspective

Although the study of microplastics in the aquatic environment incorporates a diversity of research fields, it is still in its infancy in many aspects while comparable topics have been studied in other disciplines for decades. In particular, extensive research in sedimentology can provide valuable insights to guide future microplastics research. To advance our understanding of the comparability of natural sediments with microplastics, we take an interdisciplinary look at the existing literature describing particle properties, transport processes, sampling techniques and ecotoxicology. Based on our analysis, we define seven research goals that are essential to improve our understanding of microplastics and can be tackled by learning from natural sediment research, and identify relevant tasks to achieve each goal. These goals address (1) the description of microplastic particles, (2) the interaction of microplastics with environmental substances, (3) the vertical distribution of microplastics, (4) the erosion and deposition behaviour of microplastics, (5) the impact of biota on microplastic transport, (6) the sampling methods and (7) the microplastic toxicity. When describing microplastic particles, we should specifically draw from the knowledge of natural sediments, for example by using shape factors or applying methods for determining the principal dimensions of non-spherical particles. Sediment transport offers many fundamentals that are transferable to microplastic transport, and could be usefully applied. However, major knowledge gaps still exist in understanding the role of transport modes, the influence of biota on microplastic transport, and the importance and implementation of the dynamic behaviour of microplastics as a result of time-dependent changes in particle properties in numerical models. We give an overview of available sampling methods from sedimentology and discuss their suitability for microplastic sampling, which can be used for creating standardised guidelines for future application with microplastics. In order to comprehensively assess the ecotoxicology of microplastics, a distinction must be made between the effects of the polymers themselves, their physical form, the plastic-associated chemicals and the attached pollutants. This review highlights areas where we can rely on understanding and techniques from sediment research - and areas where we need new, microplastic-specific knowledge - and synthesize recommendations to guide future, interdisciplinary microplastic research

Familieivaretakelse. Hvordan kan de operative avdelingene KJK og MJK legge til rette for en bedre ivaretakelse av sine ansatte og deres familier?

Stadig flere medarbeidere og virksomheter opplever at det er vanskelig å kombinere familieliv og arbeidsliv. Forholdet er ofte kjennetegnet av dilemmaer, konflikter og paradokser, og det er av stor betydning for den ansatte og virksomheten om arbeidsgiver er bevisst på at det er en sammenheng mellom arbeidsliv og familieliv. Flere undersøkelser viser at en velfungerende familiepolitikk ikke bare tjener medarbeideren, men at virksomheter ofte erfarer at familievennlighet gir redusert fravær og et bedre arbeidsmiljø, samtidig som det er med på å øke effektiviteten (Filstad m.fl., 2005). Bakgrunnen for at Forsvaret begynte å fokusere på familiepolitikk var tett knyttet til et behov for å rekruttere og beholde kompetent arbeidskraft. Flere undersøkelser hadde vist at hensyn til familien var viktig for avgjørelser om å slutte eller ikke (Bjønnes II-utvalg, 1997). Målsetningen til Forsvarets familiepolitikk er å legge forholdene til rette slik at en karriere i Forsvaret kan kombineres med et godt familieliv. Hensikten med denne oppgaven er å finne mer ut om hvilke faktorer som påvirker forholdet mellom familie og jobb i de oprative avdelingene Kystjegerkommandoen (KJK) og Marinejegerkommaneoen (MJK). Og hvordan avdelingen i større grad kan legge til rette for en bedre ivaretakelse av sine ansatte og deres familier. Til hjelp med å finne forskningspåstander og hypoteser har vi brukt vår relativt lange erfaring i avdelingene, samt litteratur og forskning omkring temaet. Hvor vi har sett spesilet på to samlivsundersøkelser gjort på ansatte og deres familier i hele Forsvaret, av Heen med flere i 2006 og 2011. Ut i fra rapportene fra disse to undersøkelsene, samt våre antakelser om at det er enkelte tema som er spesielt utfordrende med å jobbe i KJK og MJK har vi sett spesielt på dette med deployering til internasjonale operasjoner (INTOPS) og pendling. Oppgaven har en kvantitativ metodisk tilnærming. Som metode for innsamling av empiri ble en elektronisk spørreundersøkelse utarbeidet og sendt ut til 271 ansatte i KJK og MJK via e-post. 118 respondenter besvart spørreundersøkelsen, av disse var 36 enslige, hvilket medførte at 82 respondenter som hadde svart var innenfor målgruppen i vår undersøkelsen. Til hjelp i innhenting og analyse av data brukte vi verktøyet SurveyMonkey. Funnene våre viser at våre ansatte med familier opplever i noe grad at høy arbeidsbelastning, mye fravær fra hjemmet og lite forutsigbarhet skaper mye konflikter mellom jobb og familie. De opplever at deployering er en stor belastning for partner, mindre for barn og minst belastende for samlivet. Den største belastningen er savnet til de hjemme, mens man er deployert. Personell som deployerer opplever i større grad problemer med å kombinere jobb og familie sammenlignet med de som aldri har deployert. Likevel er det en svært lav andel av respondentene som ville vært foruten deployeringer. Videre viser våre funn at ansatte med familie opplever økt konfliktnivå på flere områder forbundet med pendling. Spesielt oppleves det at man ikke kan delta på hverdagsaktiviteter på hjemmebane som belastende. Ansatte i etablertfasen av livet, som ofte er de som har små barn, opplever mer konflikt enn de som er i andre faser av livet. Våre funn viser at de ansatte i hovedsak er positiv til det arbeidet som allerede gjøres i avdelingene for å redusere konfliktnivået mellom arbeid og familie, og over halvparten mener at arbeidet som allerede gjøres i avdelingene knyttet til familieivaretakelse bidrar til å redusere konfliktnivået mellom jobb og familie. De ansatte opplever i stor grad å få sosial støtte fra sin nærmeste leder. Dette gjelder også de som oppgir å ha barn, samt ansatte som er pendlere

Satellite peaks in the scattering of light from the two-dimensional randomly rough surface of a dielectric film on a planar metal surface.

A nonperturbative, purely numerical, solution of the reduced Rayleigh equation for the scattering of p- and s-polarized light from a dielectric film with a two-dimensional randomly rough surface deposited on a planar metallic substrate, has been carried out. It is found that satellite peaks are present in the angular dependence of the elements of the mean differential reflection coefficient in addition to an enhanced backscattering peak. This result resolves a conflict between the results of earlier approximate theoretical studies of scattering from this system

Numerical studies of the transmission of light through a two-dimensional randomly rough interface

The transmission of polarized light through a two-dimensional randomly rough interface between two dielectric media has been much less studied, by any approach, than the reflection of light from such an interface. We have derived a reduced Rayleigh equation for the transmission amplitudes when p- or s-polarized light is incident on this type of interface, and have obtained rigorous, purely numerical, nonperturbative solutions of it. The solutions are used to calculate the transmissivity and transmittance of the interface, the mean differential transmission coefficient, and the full angular distribution of the intensity of the transmitted light. These results are obtained for both the case where the medium of incidence is the optically less dense medium and in the case where it is the optically more dense medium. Optical analogues of Yoneda peaks observed in the scattering of x-rays from metallic and non-metallic surfaces are present in the results obtained in the former case. For p-polarized incident light we observe Brewster scattering angles, angles at which the diffuse transmitted intensity is zero in a single-scattering approximation, which depend on the angle of incidence in contrast to the Brewster angle for flat-surface reflection

Experimental and numerical studies of the scattering of light from a two-dimensional randomly rough interface in the presence of total internal reflection: Optical Yoneda peaks

The scattering of polarized light from a dielectric film sandwiched between two different semi-infinite dielectric media is studied experimentally and theoretically. The illuminated interface is planar, while the back interface is a two-dimensional randomly rough interface. We consider here only the case in which the medium of incidence is optically more dense than the substrate, in which case effects due to the presence of a critical angle for total internal reflection occur. A reduced Rayleigh equation for the scattering amplitudes is solved by a rigorous, purely numerical, nonperturbative approach. The solutions are used to calculate the reflectivity of the structure and the mean differential reflection coefficient. Optical analogues of Yoneda peaks are present in the results obtained. The computational results are compared with experimental data for the in-plane mean differential reflection coefficient, and good agreement between theory and experiment is found

Oxidation of methane in seawater - Laboratory experiments and the use of models - OC2022 A-114

Oxidation of methane was determined in this project by two methods: Stable isotope analyses (13CH4) and by the use of tritium-labelled methane (3H-CH4). The intentions of the project were to obtain methane oxidation rates for the marine water column, which may be of relevance for the Norwegian Continental Shelf. Experimental, sampling, and analytical methods were established for both methods. Relatively few experiments were of a quality considered to be acceptable. The oxidation data determined by the two methods resulted in half-lives of 21.6 ± 6.2 days at 5°C incubation temperature with the stable isotope method, and 5.6 ± 0.7 and 4.6 ± 2.5 days with the tritium method at 5 to 8.5°C incubation temperature, respectively. Based on the comparison to data for field studies, it seemed that the data obtained by the tritium methods represented an overestimation of methane oxidation rates, while the stable isotope data were more in agreement with field data. The oxidation data were used in model simulations to determine atmospheric releases of methane from seeps at different seep depths.Oxidation of methane in seawater - Laboratory experiments and the use of models - OC2022 A-114publishedVersio