Multiply subtractive generalized Kramers-Kronig relations: application on third harmonic generation susceptibility on polysilane

We present multiply subtractive Kramers-Kronig (MSKK) relations for the moments of arbitrary order harmonic generation susceptibility. Using experimental data on third-harmonic wave from polysilane, we show that singly subtractive Kramers-Kronig (SSKK) relations provide better accuracy of data inversion than the conventional Kramers-Kronig (K-K) relations. The fundamental reason is that SSKK and MSKK relations have strictly faster asymptotic decreasing integrands than the conventional K-K relations. Therefore SSKK and MSKK relations can provide a reliable optical data inversion procedure based on the use of measured data only.Comment: 14 pages, 2 figure

Cultural tourism: new opportunities for diversifying the tourism industry in Botswana

Botswana is known as a wilderness and safari-tourism destination, which attracts high-end overseas visitors to the country. Since the 1990s the country’s tourism policy has been based on a so called ‘High Value – Low Volume’ (HVLV) strategy referring to the aim of attracting limited numbers of tourists with high expenditure patterns. However, while such tourism operations have contributed to the Gross Domestic Product (GDP) of the country and offered investment opportunities for international companies, the position of Botswana as a HVLV destination is increasingly criticised. It is seen as offering too narrow prospects for the growth of the industry and for the local participation and benefit sharing in tourism in future. Hence, there is a need for diversification of the product with deeper involvement of local people to tourism. Therefore, communities and Botswana’s cultural and heritage attractions are increasingly seen as one of the future cornerstones of tourism development. This paper provides an overview of cultural tourism with specific reference to existing cultural and heritage attractions and the potential thereof for tourism in Botswana. The paper concludes that while the role of culture is still underutilised in tourism, the cultural tourism in Botswana has the potential to contribute to a more equitable distribution of tourism-based development and the related benefits for local communities

Efficacy Of Natural Plant Extracts In Antimicrobial Packaging Systems

Antimicrobial plant extracts used in food packaging provide a healthy packaging alternatives. They contain aromatic and phenolic compounds that are responsible for their antibacterial properties. In this study, we report the antibacterial effects of extracts obtained from sea buckthorn (Hippophaë rhamnoides L.) leaves, and inner bark of pine trees (Pinus silvestris) that were applied as coatings on paper suitable for packaging application. Extracts from sea buckthorn leaves exhibited antibacterial effect both as a solvent extract and as a coating on paper against Pseudomonas aeruginosa as test bacteria. However, coatings of pine bark extract did not exhibit antibacterial effect as coatings even though the solvent extracts exhibited antibacterial effects. Staphylococcus aureus demonstrated resistance towards both plant extracts after they had been applied as coatings on paper for packaging

Antibacterial Activity of Electrodeposited Copper and Zinc on Metal Injection Molded (MIM) Micropatterned WC-CO Hard Metals

Antibacterial activity of electrodeposited copper and zinc both on flat and micropatterned hard metal tungsten carbide-cobalt (WC-Co) specimens was studied. Tribological wear was applied on electrodeposited specimens: coatings were completely removed from flat surfaces whereas only top of the micropillars was exposed to wear for the micropatterned specimens protecting the functional metal coating in between the micropillars. The growth of Staphylococcus aureus (S. aureus) Gram-positive bacterial species was studied on the specimens using a touch test mimicking bacterial transfer from the surfaces. Copper coated specimens prevented bacterial growth completely independent of wear or surface structure, i.e., even residual traces of copper were sufficient to prevent bacterial growth. Zinc significantly suppressed the bacterial growth both on flat and micropatterned specimens. However, adhesion of zinc was low resulting in an easy removal from the surface by wear. The micropatterned zinc specimens showed antibacterial activity as electrodeposited zinc remained intact on the sample surface between the micropillars. This was sufficient to suppress the growth of S. aureus. On the contrary, the flat zinc coated surfaces did not show any antibacterial activity after wear. Our results show that micropatterned hard metal specimens can be used to preserve antibacterial activity under tribological wear

Antimicrobial characterization of silver nanoparticle-coated surfaces by “touch test” method

Abstract: Bacterial infections, especially by antimicrobial resistant (AMR) bacteria, are an increasing problem worldwide. AMR is especially a problem with health care-associated infections due to bacteria in hospital environments being easily transferred from patient to patient and from patient to environment, and thus, solutions to prevent bacterial transmission are needed. Hand washing is an effective tool for preventing bacterial infections, but other approaches such as nanoparticle-coated surfaces are also needed. In the current study, direct and indirect liquid flame spray (LFS) method was used to produce silver nanoparticle-coated surfaces. The antimicrobial properties of these nanoparticle surfaces were evaluated with the “touch test” method against Escherichia coli and Staphylococcus aureus. It was shown in this study that in glass samples one silver nanoparticle-coating cycle can inhibit E. coli growth, whereas at least two coating cycles were needed to inhibit S. aureus growth. Silver nanoparticle-coated polyethylene (PE) and PE terephthalate samples did not inhibit bacterial growth as effectively as glass samples: three nanoparticle-coating cycles were needed to inhibit E. coli growth, and more than 30 coating cycles were needed until S. aureus growth was inhibited. To conclude, with the LFS method, it is possible to produce nanostructured large-area antibacterial surfaces which show antibacterial effect against clinically relevant pathogens. Results indicate that the use of silver nanoparticle surfaces in hospital environments could prevent health care-associated infections in vivo.</p

Characterization of flame coated nanoparticle surfaces with antibacterial properties and the heat-induced embedding in thermoplastic-coated paper

Silver nanoparticles deposited on surfaces can provide an antibacterial effect with potential uses in, for example, health-care settings. However, release of nanoparticles and their potential exposure to the environment is of concern. The current work demonstrates a continuous synthesis that simultaneously deposits silver nanoparticles onto plastic coated paper surface by utilizing the liquid flame spray (LFS) aerosol process. Heat from LFS is used to soften the thermoplastic paper surface, which enables partial and full embedding of the nanoparticles, thereby improving adhesion. The embedding is confirmed with atomic force and scanning electron microscopy, and the deposited silver amounts are quantified with X-ray photoelectron spectroscopy. The results suggest that embedding was more effective in PE-coated paper samples due to the lower glass transition temperature when compared to PET-coated paper samples. The antibacterial properties of the surfaces against E. coli and S. aureus were maintained and confirmed with a previously developed 'Touch-Test Method: The LFS process has the potential to be used for large-scale manufacturing of antibacterial surfaces with improved nanoparticle adhesion on appropriately chosen thermoplastic surfaces

Functionalization of TiO2 inverse opal structure with atomic layer deposition grown Cu for photocatalytic and antibacterial applications

TiO2 inverse opal (IO) structure surfaces were functionalized with a sub-monolayer amount of Cu by atomic layer deposition (ALD) and tested for photocatalytic and antimicrobial applications. Decomposition of acetylene (C2H2) into CO2 and reduction of CO2 into CH4 were tested in the gas phase and photodegradation of methylene blue (MB) was tested in the liquid phase. Antimicrobial activity was tested against Gram-positive Staphylococcus aureus (S. aureus) bacteria. ALD Cu without any post-deposition heat treatment (HT) decreased the photo degradation rate of both C2H2 and MB but improved the activity towards CO2 reduction. ALD Cu increased MB photodegradation rate and antimicrobial activity only after HT at 550 C, which was linked to the improved chemical stability Cu after the HT. The same HT decreased the activity towards CO2 reduction and decomposition of C2H2. The HT induced desorption of loosely bound ALD Cu+/2+ from the TiO2 IO surface and the remaining Cu+/2+ was reduced to Cu+. The photocatalytic and antimicrobial activity of TiO2 IO can be tailored by the addition of a sub-monolayer amounts of Cu with performance depending on the targeted reaction

Nanophotonics on Paper Platform

This work concentrated on three nanophotonic applications based on printed and coated functionality on natural fibre based substrates. Hence, the thesis deals with three emerging fields: nanotechnology, nanophotonics, and sustainable materials. Nanotechnology tools have been developed over the past few decades increasing tremendously our abilities to control matter in nanoscale. This has resulted in the growth of nanophotonics, i.e. how light can be controlled by nanoscale structures and particles. This work concentrates on TiO2 and silver nanoparticles, and their applications on paperboard substrate. Demands for sustainability have grown significantly in recent years with growing population and emerging environmental issues. Nanotechnology is an ideal tool for promoting sustainability: with less material and energy consumption one can generate the same or even enhanced properties. Combining such nanoscale structures with renewable materials provides a double advantage compared to the traditional solutions. First, photocatalytic activity of liquid flame spray (LFS) deposited TiO2 nanoparticles on paperboard was utilized for controlled wettability. It has been shown earlier that it is possible to convert an initially superhydrophobic surface into a highly hydrophilic one by ultraviolet A (UVA) irradiation. However, this process is reversible and the initial superhydrophobicity is returned within 60 days in storage. In this work a protocol was developed for making the wettability conversion permanent by first stage wetting, i.e. by exposing the UVA irradiated TiO2 nanoparticles to water that removed the nanoparticles from the irradiated area permanently. Additionally, durability of such nanoparticle coated paperboard under compression was studied. Surface-enhanced Raman scattering (SERS) activity was demonstrated by LFS deposited silver nanoparticles on glass substrate, thereafter expanded to paperboard surfaces. A problem with paperboard for SERS analysis is background luminescence, which is typically orders of magnitude larger than the Raman signal, and which thereby easily dominates the measured spectrum. Two different solutions for SERS active paperboard substrates were developed. First, inkjet printing with commercial silver nanoparticle ink was found suitable for SERS activity but only with a full silver coverage on paperboard blocking the luminescence from the base paperboard. A more cost-effective solution was developed by using a simple carbon coating by flexography that allowed even individual LFS deposited silver nanoparticles for SERS measurements on paperboard with significantly reduced silver amount and consequently, cost. Finally, commercial TiO2 nanoparticles were used together with methylene blue (MB) organic dye. MB has a distinct blue color in the oxidized form that can be converted to the transparent leucomethylene blue form by UVA activation together with TiO2 nanoparticles. Therefore, functional ink combining MB with TiO2 nanoparticles was shown to be suitable for costefficient oxygen indicators. Both reverse gravure coated and flexographic printed indicator labels were demonstrated that are suitable for simple oxygen indicators, for example, in modified atmosphere packages. The use of metal and metal oxide nanostructures as functional light-activated materials enables creation of both cost-efficient and environmentally sound products, which can be widely used in society enabling a break-through in transformation from the current fossil fuel based economy to a solar driven economy. Therefore, as a summary, it is believed that the results of the thesis can lay ground for the development of new large-scale, nanostructured light-activated materials on natural fibre based substrates providing sustainable solutions for future generations.Detta arbete koncentrerade sig på tre nanofotoniska applikationer som baserar sig på tryckt och bestruken funktionalitet på naturfiberbaserade substrat. Avhandlingen behandlar tre nya områden: nanoteknologi, nanofotonik och hållbara material. Nanotekniska verktyg har utvecklats under de senaste decennierna och ökat enormt vår förmåga att kontrollera materia i nanoskala. Detta har resulterat i tillväxt av nanofotonik, dvs. hur ljus kan styras av strukturer och partiklar i nanoskala. Detta arbete koncentrerar sig på TiO2- och silvernanopartiklar och deras applikationer på kartongunderlag. Kraven på hållbarhet har vuxit betydligt under de senaste åren samtidigt med ökande befolkning och växande miljöproblem. Nanoteknologi är ett idealt verktyg för främjande av hållbarhet: med mindre material- och energiförbrukning kan man generera samma eller till och med förbättrade egenskaper. Genom att kombinera sådana strukturer i nanoskala med förnybara material fördubblas fördelen jämfört med de traditionella lösningarna. Fotokatalytisk aktivitet av TiO2-nanopartiklar som utfällts med flytande flamspray (LFS) på kartong användes för kontrollerad vätningsförmåga. Det har tidigare visats att det är möjligt att konvertera en initialt superhydrofob yta till i en hög grad hydrofil yta via ultraviolett A (UVA)-aktivering. Denna process är dock reversibel och den initiala superhydrofobiciteten återkommer inom 60 dagars lagring. I detta arbete utvecklades en metod för att göra vätningsförmågans konvertering permanent genom vätning av första steget, dvs. genom att utsätta de UVA-aktiverade TiO2-nanopartiklarna för vatten som permanent avlägsnade nanopartiklarna från det strålade ytan. Dessutom undersöktes hållbarheten för en nanopartikelbelagd kartong under kompression. Aktiviteten av ytförstärkt Raman-spridning (SERS) demonstrerades med hjälp av LFS-deposition av silverpartiklar på glassubstrat och senare på kartongytor. Ett problem med kartong för SERS-analys är bakgrundsluminescensen som är normalt några storleksordningar större än Raman-signalen och därför enkelt dominerar det mätta spektrumet. Två olika lösningar för SERS-aktiva kartong utvecklades. Den första var bläckstråletryckning med en kommersiell nanopartikulär silvertryckfärg som var lämplig för SERS-aktivitet men endast då kartongytan var totalt täckt så att luminescensen från kartongen blockerades. En mer kostnadseffektiv lösning utvecklades genom att använda en enkel kolbeläggning med hjälp av flexografi som möjliggjorde även SERS-analys av individuella LFS-deponerade silverpartiklar på kartong vilket reducerade silvermängden och kostnaderna. Slutligen användes kommersiella TiO2-nanopartiklar tillsammansmed ett organiskt färgämne, metylenblå (MB). MB har en distinkt blå färg i oxiderad form som kan omvandlas till den genomskinliga leukometylenblå genom UVA-aktivering tillsammans med TiO2-nanopartiklar. Därför visade sig det funktionella bläcket som kombinerar MB med TiO2-nanopartiklar vara lämpligt för kostnadseffektiva syreindikatorer. Både omvänd gravyrbelagda och flexografitryckta indikatoretiketter, som är lämpliga för t.ex. enkla syreindikatorer i förpackningar med modifierad atmosfär, demonstrerades. Användning av metall- och metalloxidnanostrukturer som funktionella ljusaktiverade material möjliggör skapande av både kostnadseffektiva och miljöanpassade produkter som kan i stor utsträckning användas i samhället, och som möjliggör ett genombrott i omvandlingen från en ekonomi baserad på fossilt bränsle till en solstyrd ekonomi. Sammanfattningsvis, resultaten från denna avhandling kan antas ge en bas för utveckling av nya storskaliga, nanostrukturerade ljusaktiverade material på naturfiberbaserade substrat som ger hållbara lösningar för kommande generationer