Local structure of water studied by Compton scattering

This thesis presents a novel application of x-ray Compton scattering to structural studies of molecular liquids. Systematic Compton-scattering experiments on water have been carried out with unprecedented accuracy at third-generation synchrotron-radiation laboratories. The experiments focused on temperature effects in water, the water-to-ice phase transition, quantum isotope effects, and ion hydration. The experimental data is interpreted by comparison with both model computations and ab initio molecular-dynamics simulations. Accordingly, Compton scattering is found to provide unique intra- and intermolecular structural information. This thesis thus demonstrates the complementarity of the technique to traditional real-space probes for studies on the local structure of water and, more generally, molecular liquids.Vesi on tärkeimpiä yhdisteitä elämän kannalta. Vaikka vettä on tutkittu laajalti, ei sen kaikkia ominaisuuksia ole vieläkään kyetty mallintamaan. Tässä väitöskirjatyössä on kehitetty uutta röntgensäteilyn sirontaan perustuvaa menetelmää veden lähirakenteen tutkimiseen molekyylitasolla. Niin sanottujen Compton-sirontamitttausten avulla on tutkittu muun muuassa lämpötilan ja sulamisen vaikutusta vesimolekyylien lähirakenteeseen sekä erilaisia suolaliuoksia. Kokeellinen työ on tehty kehittyneimmillä synkrotronisäteilylähteillä yhteiseurooppalaisessa ESRF:ssä (Grenoble, Ranska) ja SPring-8:ssa (Hyogo,Japani). Aiempaa selvästi tarkempien kokeellisten mittausten avulla on voitu havaita vettä lämmitettäessä sen vetysidosverkostossa tapahtuvia erittäin pieniä muutoksia. Teoreettisten mallien avulla on voitu edelleen osoittaa kytkentä vetysidoksen ja vesimolekyylin sisäisen rakenteen muutoksen välillä. Saavutetut tulokset ovat merkittäviä veden rakenteen perustutkimuksen kannalta muodostamalla entistä täsmällisemmän perustan kehittyneille vesimalleille.Vatten är ett av de viktigaste föreningarna för levande organismer. Trots livlig forskning saknas ännu en modell som kan förklara alla dess egenskaper. Avhandlingen beskriver en ny metod för studier av vattnets närstruktur på molekylnivå, baserad på spridning av röntgenstrålning. Inverkan av bland annat temperatur och smältning på vattnets närstruktur samt saltlösingar har undersökts med hjälp av så kallad Compton-spridning. Experimenten har gjorts vid de mest avancerade synkrotronstrålningslaboratorierna: det sameuropeiska ESRF (Grenoble, Frankrike) och SPring-8 (Hyogo, Japan). De avsevärt noggrannare experimenten, jämfört med tidigare, har möjliggjort observationen av små förändringar i det så kallade vätebindningsnätverket vid uppvärmning av vatten. Med hjälp av teoretiska modeller har vidare en koppling mellan förändringar i vätebindningen och vattenmolekylens interna struktur kunnat påvisas. Resultaten är av betydelse för grundforskning inriktad på vattnets struktur, i och med att de bildar en exaktare grund än hittillsvarande för avancerade vattenmodeller

Spin-polarized transport through carbon nanotubes

Carbon nanotubes (CNT) belong to the most promising new materials which can in the near future revolutionize the conventional electronics. When sandwiched between ferromagnetic electrodes, the CNT behaves like a spacer in conventional spin-valves, leading quite often to a considerable giant magneto-resistance effect (GMR). This paper is devoted to reviewing some topics related to electron correlations in CNT. The main attention however is directed to the following effects essential for electron transport through nanotubes: (i) nanotube/electrode coupling and (ii) inter-tube interactions.It is shown that these effects may account for some recent experimental reports on GMR, including those on negative (inverse) GMR.Comment: 7 pages, 3 figure

Prevention of HPV-Related Cancers in Norway: Cost-Effectiveness of Expanding the HPV Vaccination Program to Include Pre-Adolescent Boys

Background: Increasingly, countries have introduced female vaccination against human papillomavirus (HPV), causally linked to several cancers and genital warts, but few have recommended vaccination of boys. Declining vaccine prices and strong evidence of vaccine impact on reducing HPV-related conditions in both women and men prompt countries to reevaluate whether HPV vaccination of boys is warranted. Methods: A previously-published dynamic model of HPV transmission was empirically calibrated to Norway. Reductions in the incidence of HPV, including both direct and indirect benefits, were applied to a natural history model of cervical cancer, and to incidence-based models for other non-cervical HPV-related diseases. We calculated the health outcomes and costs of the different HPV-related conditions under a gender-neutral vaccination program compared to a female-only program. Results: Vaccine price had a decisive impact on results. For example, assuming 71% coverage, high vaccine efficacy and a reasonable vaccine tender price of $75 per dose, we found vaccinating both girls and boys fell below a commonly cited cost-effectiveness threshold in Norway ($83,000/quality-adjusted life year (QALY) gained) when including vaccine benefit for all HPV-related diseases. However, at the current market price, including boys would not be considered ‘good value for money.’ For settings with a lower cost-effectiveness threshold ($30,000/QALY), it would not be considered cost-effective to expand the current program to include boys, unless the vaccine price was less than$36/dose. Increasing vaccination coverage to 90% among girls was more effective and less costly than the benefits achieved by vaccinating both genders with 71% coverage. Conclusions: At the anticipated tender price, expanding the HPV vaccination program to boys may be cost-effective and may warrant a change in the current female-only vaccination policy in Norway. However, increasing coverage in girls is uniformly more effective and cost-effective than expanding vaccination coverage to boys and should be considered a priority

Rapid Evolutionary Adaptation to Diet Composition in the Black Soldier Fly (Hermetia illucens)

Genetic adaptation of Hermetia illucens (BSF) to suboptimal single sourced waste streams can open new perspectives for insect production. Here, four BSF lines were maintained on a single sourced, low-quality wheat bran diet (WB) or on a high-quality chicken feed diet (CF) for 13 generations. We continuously evaluated presumed evolutionary responses in several performance traits to rearing on the two diets. Subsequently, we tested responses to interchanged diets, i.e., of larvae that had been reared on low-quality feed and tested on high-quality feed and vice versa to evaluate costs associated with adaptation to different diets. BSF were found to experience rapid adaptation to the diet composition. While performances on the WB diet were always inferior to the CF diet, the adaptive responses were stronger to the former diet. This stronger response was likely due to stronger selection pressure experienced by BSF fed on the low-quality single sourced diet. The interchanged diet experiment found no costs associated with diet adaptation, but revealed cross generational gain associated with the parental CF diet treatment. Our results revealed that BSF can rapidly respond adaptively to diet, although the mechanisms are yet to be determined. This has potential to be utilized in commercial insect breeding to produce lines tailored to specific diets.</p

Density fluctuations of hard-sphere fluids in narrow confinement

Spatial confinement induces microscopic ordering of fluids, which in turn alters many of their dynamic and thermodynamic properties. However, the isothermal compressibility has hitherto been largely overlooked in the literature, despite its obvious connection to the underlying microscopic structure and density fluctuations in confined geometries. Here, we address this issue by probing density profiles and structure factors of hard- sphere fluids in various narrow slits, using x-ray scattering from colloid-filled nanofluidic containers and integral-equation-based statistical mechanics at the level of pair distributions for inhomogeneous fluids. Most importantly, we demonstrate that density fluctuations and isothermal compressibilities in confined fluids can be obtained experimentally from the long-wavelength limit of the structure factor, providing a formally exact and experimentally accessible connection between microscopic structure and macroscopic, thermodynamic properties. Our approach will thus, for example, allow direct experimental verification of theoretically predicted enhanced density fluctuations in liquids near solvophobic interfaces