Granular Rayleigh-Taylor Instability: Experiments and Simulations

A granular instability driven by gravity is studied experimentally and numerically. The instability arises as grains fall in a closed Hele-Shaw cell where a layer of dense granular material is positioned above a layer of air. The initially flat front defined by the grains subsequently develops into a pattern of falling granular fingers separated by rising bubbles of air. A transient coarsening of the front is observed right from the start by a finger merging process. The coarsening is later stabilized by new fingers growing from the center of the rising bubbles. The structures are quantified by means of Fourier analysis and quantitative agreement between experiment and computation is shown. This analysis also reveals scale invariance of the flow structures under overall change of spatial scale.Comment: 4 pages, 11 figure

Parafinvoks forståelse og kontroll - Produkt- og markedsanalyse

Denne masteroppgaven omhandler teori og eksperimentelt arbeid for dannelse av parafinvoks og effektene som oppnås ved å tilsette to ulike kjemikaler levert av Jotun. I tillegg presenterer oppgaven en PESTEL-analyse som tar for seg faktorer i samfunnet som påvirker Jotuns muligheter for å etablere seg i det eksisterende markedet av voksinhibitorer. Målet med oppgaven har vært å studere hvordan to kjemikaler levert av Jotun påvirker dannelse, struktur og hardhet av parafinvoks. Dannelse av parafinvoks er et problem som oppstår i rør og annet utstyr ved produksjon av olje og gass. Dette problemet danner en ekstra kostnad for produksjonen ved at det må tilsettes ekstra kjemikaler eller utføres andre operasjoner for å hindre avsatt parafinvoks. I denne oppgaven har to ulike kjemikaler blitt tilsatt en simulert råoljeproduksjon, hvor en kaldfinger og en avsetningsplate har blitt brukt for å utføre reologiske målinger av den avsatte voksen. Metoden som har blitt brukt er basert på metodeutviklingen som ble gjennomført i 2018. I tillegg har det blitt benyttet en gasskromatograf for å studere de kjemiske sammensetningene av den avsatte voksen. Inhibitorenes effekt på mengde avsatt voks, kjemisk sammensetning og reologi har vært de sentrale områdene som har blitt studert. Effekten av de to forskjellige inhibitorene har vært varierende. Inhibitor 1 har ikke hatt noen effekt på den avsatte voksen, mens inhibitor 2 har medført en reduksjon i storage modulus ved en konsentrasjon på 750 ppm eller høyere, samt en reduksjon i komponenter med lang kjedelengde ved konsentrasjoner på 3000 ppm eller høyere

Family-Vicsek scaling of detachment fronts in Granular Rayleigh Taylor Instabilities during sedimenting granular/fluid flows

When submillimetric particles are confined in a fluid such that a compact cluster of particles lie above the clear fluid, particles will detach from the lower boundary of the cluster and form an unstable separation front giving rise to growing fingers of falling particles. We study this problem using both experiments and hybrid granular/fluid mechanics models. In the case of particles from 50 to 500 microns in diameter falling in air, we study the horizontal density fluctuations at early times: the amplitude of the density difference between two points at a certain horizontal distance grows as a power law of time. This happens up to a saturation corresponding to a power law of the distance. The way in which the correlation length builds up to this saturation also follows a power law of time. We show that these decompaction fronts in sedimentation problems follow a Family-Vicsek scaling, characterize the dynamic and Hurst exponent of the lateral density fluctuations, respectively z \sim 1 and \zeta \sim 0.75, and show how the prefactors depend on the grain diameter. We also show from similar simulations with a more viscous and incompressible fluid, that this feature is independent of the fluid compressibility or viscosity, ranging from air to water/glycerol mixtures

FORSVARETS MARKEDSEKSPONERING: Har Forsvarets markedseksponering påvirket vernepliktige ved Forsvarets Spesialstyrker i kontingent 2008 sine forberedelser til opptak?

Tema for denne Bacheloroppgaven er Forsvarets markedseksponering og påvirkningen det har på kandidaters forberedelser til opptak. Bakgrunn for temaet er at Forsvaret, som andre organisasjoner, er avhengig av personell og derfor trenger å tiltrekke seg det best kvalifiserte personellet. Markedsføring er et viktig ledd i Forsvarets rekrutteringsprosess og representerer en stor del av Forsvarets kommunikasjon utad. Vi valgte å gjennomføre en casestudie på Forsvarets Spesialkommando (FS), siden deres vernepliktige tjeneste er søknadsbasert og består av en relativt homogen gruppe. Problemstillingen er derfor som følger; Har Forsvarets markedseksponering påvirket vernepliktige ved Forsvarets Spesialstyrker i kontingent 2008 sine forberedelser til opptak? Vår casestudie kombinerte kvantitativ og kvalitativ undersøkelsesmetode i den hensikt å belyse fenomenet helhetlig. Dette ble gjort gjennom en spørreundersøkelse på aspirantene i kontingent 2008, og intervju av ansatte med tilknytning til rekruttering og seleksjon i avdelingen. Resultatene fra undersøkelsene ble deretter diskutert i lys av markedsførings og motivasjonsteori. Vi konkluderer med at Forsvarets markedseksponering har en grad av påvirkning på de vernepliktige i kontingent 2008 sine forberedelser til opptak. Markedseksponeringen har tilsynelatende formet enkeltes forventninger, motivasjon og inntrykk av tjenestens innhold ved avdelingen. Det har resultert i motivasjon og atferdsendring hos flere kandidater, synliggjort gjennom endrede forberedelser til opptaket. Konsekvensene for vår forskning er blant annet at den bidrar med kunnskap innen et tema som er lite forsket på. En anbefaling til videre forskning blir derfor å undersøke hvilke typer mennesker som blir tiltrukket av Forsvarets markedseksponering, og hvorvidt disse menneskene er de FS faktisk ønsker å ansette.publishedVersio

Characterization of rockfalls from seismic signal: insights from laboratory experiments

International audienceThe seismic signals generated by rockfalls can provide information on their dynamics and location. However, the lack of field observations makes it difficult to establish clear relationships between the characteristics of the signal and the source. In this study, scaling laws are derived from analytical impact models to relate the mass and the speed of an individual impactor to the radiated elastic energy and the frequency content of the emitted seismic signal. It appears that the radiated elastic energy and frequencies decrease when the impact is viscoelastic or elasto-plastic compared to the case of an elastic impact. The scaling laws are validated with laboratory experiments of impacts of beads and gravels on smooth thin plates and rough thick blocks. Regardless of the involved materials, the masses and speeds of the impactors are retrieved from seismic measurements within afactor of 3. A quantitative energy budget of the impacts is established. On smooth thin plates, the lost energy is either radiated in elastic waves or dissipated in viscoelasticity when the impactor is large or small with respect to the plate thickness, respectively. In contrast, on rough thick blocks, theelastic energy radiation represents less than 5% of the lost energy. Most of the energy is lost in plastic deformation or rotation modes of the bead owingto surface roughness. Finally, we estimate the elastic energy radiated during field scale rockfalls experiments. This energy is shown to be proportional to the boulder mass, in agreement with the theoretical scaling laws

Next-Generation Biomaterials for Food Packaging Applications

During the recent years, environmentally friendly packaging has become increasingly important for the consumer. However, this shift towards a greener alternative should not come as a compromise on the safety of the product being packaged. The main aim of this study was to investigate two different biopolymers and their usage as packaging material for food packaging applications. Films made from natural biopolymers such as chitosan and alginate were made, and their functional properties were studied. However, in order to achieve films with enhanced functional properties (mechanical, barrier, etc.) suitable for food packaging applications, seaweed was added to the film forming solution followed by HPP treatment. Chitosan is typically dissolved in acetic acid, which has a quite pungent smell which might lead to rejection by the consumer. Thus, it was investigated if citric acid as a solvent could compare to the properties of chitosan-acetic acid films. The films made with the two different acids showed similar water vapor transmission rates. However, chitosan-acetic acid films were tougher, more flexible and had a higher concentration of free amino groups. Nevertheless, films made with both citric and acetic acid were observed to have relatively good antioxidant properties. HPP treatment was performed on the film-forming solution prior to casting the films. Generally, HPP treatment at pressures of 200 and 600 MPa either decreased the properties in the chitosan films, or the properties remained unchanged. In addition, seaweed was added in different concentrations to investigate if the properties of the chitosan films could improve. However, no such improvement was seen except for increased antioxidant activity at high seaweed concentrations. Alginate is dissolved in water, so only the effect of HPP treatment and seaweed addition was studied for this polymer. HPP treatment showed some promising effects on the tensile strength of the alginate films at 200 MPa pressure. However, the barrier properties in the films remained unchanged by HPP treatment. Some decrease in antioxidant activity was observed with HPP treatment at 600 MPa pressure. Addition of seaweed showed more promising results. The antioxidant activity of the alginate films increased with added seaweed and some improvement was seen in the WVTR. Nevertheless, the tensile strength of the films was not improved by addition of seaweed, and the elasticity decreased. Both chitosan and seaweed has been reported to have good antimicrobial properties. These properties were investigated by two types of assays: disc diffusion and liquid-based assays. The disc diffusion assay was not successful due to the films curling in on themselves upon contact with the slight wet media. However, two liquid-based assays were performed at both ideal growth temperate of 37 °C, and 10 °C to simulate more realistic storage temperatures. Chitosan made with citric acid or acetic acid showed higher antimicrobial effect against E. coli than S. aureus at both 24 h incubation at 37 °C and 5 and 10 days incubation at 10 °C. The log concentration in the chitosan samples was below the detection limit for E. coli after 5 and 10 days incubation at 10 °C. Seaweed had no antimicrobial effect at 37 °C, however, some effect was seen for S. aureus at 10 °C. The combination of chitosan and seaweed was also studied at 10 °C. Reduction in CFU/mL were observed for both E. coli and S. aureus after 5 and 10 days incubation at 10 °C, however, the effect was biggest for S. aureus with a complete inhibition after 10 days incubation at 10 °C

Secure and scalable dataprocessing and communications for an Animal Tracking System

Modern technology is constantly being employed in new fields, by new industries and people. The cost of advanced technological equipment decreases continously, and equipment that was reserved for people and corporations with a lot of money has now become household products. This enables many interesting ideas and projects, Kitron Development’s radiocollar project being one of them. Kitron Development is involved in a project to track the position of animals by substituting the traditional bell collar with a collar that contains a GPS receiver. The collar transmits its position to a base station using VHF radio, and the base station forwards the received data to a central using cellular technology. In this thesis we have surveyed, designed and implemented the central, called Animal Tracking System, that receives and processes data from the base stations. The Animal Tracking System consists of four different components that work together. A server that communicates with the base station, and stores data in a database, an alarm monitor that survey the data in the database and a web application that allow the farmers to view data about their animals, as well as configure the system

Next-Generation Biomaterials for Food Packaging Applications

During the recent years, environmentally friendly packaging has become increasingly important for the consumer. However, this shift towards a greener alternative should not come as a compromise on the safety of the product being packaged. The main aim of this study was to investigate two different biopolymers and their usage as packaging material for food packaging applications. Films made from natural biopolymers such as chitosan and alginate were made, and their functional properties were studied. However, in order to achieve films with enhanced functional properties (mechanical, barrier, etc.) suitable for food packaging applications, seaweed was added to the film forming solution followed by HPP treatment. Chitosan is typically dissolved in acetic acid, which has a quite pungent smell which might lead to rejection by the consumer. Thus, it was investigated if citric acid as a solvent could compare to the properties of chitosan-acetic acid films. The films made with the two different acids showed similar water vapor transmission rates. However, chitosan-acetic acid films were tougher, more flexible and had a higher concentration of free amino groups. Nevertheless, films made with both citric and acetic acid were observed to have relatively good antioxidant properties. HPP treatment was performed on the film-forming solution prior to casting the films. Generally, HPP treatment at pressures of 200 and 600 MPa either decreased the properties in the chitosan films, or the properties remained unchanged. In addition, seaweed was added in different concentrations to investigate if the properties of the chitosan films could improve. However, no such improvement was seen except for increased antioxidant activity at high seaweed concentrations. Alginate is dissolved in water, so only the effect of HPP treatment and seaweed addition was studied for this polymer. HPP treatment showed some promising effects on the tensile strength of the alginate films at 200 MPa pressure. However, the barrier properties in the films remained unchanged by HPP treatment. Some decrease in antioxidant activity was observed with HPP treatment at 600 MPa pressure. Addition of seaweed showed more promising results. The antioxidant activity of the alginate films increased with added seaweed and some improvement was seen in the WVTR. Nevertheless, the tensile strength of the films was not improved by addition of seaweed, and the elasticity decreased. Both chitosan and seaweed has been reported to have good antimicrobial properties. These properties were investigated by two types of assays: disc diffusion and liquid-based assays. The disc diffusion assay was not successful due to the films curling in on themselves upon contact with the slight wet media. However, two liquid-based assays were performed at both ideal growth temperate of 37 °C, and 10 °C to simulate more realistic storage temperatures. Chitosan made with citric acid or acetic acid showed higher antimicrobial effect against E. coli than S. aureus at both 24 h incubation at 37 °C and 5 and 10 days incubation at 10 °C. The log concentration in the chitosan samples was below the detection limit for E. coli after 5 and 10 days incubation at 10 °C. Seaweed had no antimicrobial effect at 37 °C, however, some effect was seen for S. aureus at 10 °C. The combination of chitosan and seaweed was also studied at 10 °C. Reduction in CFU/mL were observed for both E. coli and S. aureus after 5 and 10 days incubation at 10 °C, however, the effect was biggest for S. aureus with a complete inhibition after 10 days incubation at 10 °C

Hedging, exposure and rm value: A study of European and U.S. Airlines

For several reasons, the airline industry is a reasonable industry to analyze the relation between corporate risk exposure, hedging policy, and rm value. We ex- plore the relationship between hedging, exposure, and rm value among European and U.S. airlines. More speci cally, how di erences in strategy between Low-Cost Carriers and Full-Service Airlines a ects this relationship, during the period Jan 1, 2010 { Dec 31, 2017. We analyze the relation between airlines fuel exposure coe cients and the percentage of next year's fuel requirement hedged. We nd evidence that hedging reduces exposure to fuel prices. Further, investgating the relationship between hedging and rm value, we nd that hedging is associated with higher rm value. However, we discover that di erences in strategy a ects the hedging premium. Our results con rms that increased hedging activity in periods of high exposure is not associated with higher rm value. Lastly, we nd that alleviating the underinvestment problem appear not to be important in explaining airlines hedging behavior