| 1. |
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| 2. |
- Gogova, Daniela, et al.
(author)
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Epitaxial growth of β -Ga 2 O 3 by hot-wall MOCVD
- 2022
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In: AIP Advances. - : AIP Publishing. - 2158-3226. ; 12:5, s. 055022-055022
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Journal article (peer-reviewed)abstract
- The hot-wall metalorganic chemical vapor deposition (MOCVD) concept, previously shown to enable superior material quality and highperformance devices based on wide bandgap semiconductors, such as Ga(Al)N and SiC, has been applied to the epitaxial growth ofβ-Ga2O3. Epitaxial β-Ga2O3 layers at high growth rates (above 1 μm/h), at low reagent flows, and at reduced growth temperatures(740 ○C) are demonstrated. A high crystalline quality epitaxial material on a c-plane sapphire substrate is attained as corroborated by a combination of x-ray diffraction, high-resolution scanning transmission electron microscopy, and spectroscopic ellipsometry measurements. Thehot-wall MOCVD process is transferred to homoepitaxy, and single-crystalline homoepitaxial β-Ga2O3 layers are demonstrated with a 201 ¯rocking curve width of 118 arc sec, which is comparable to those of the edge-defined film-fed grown (201) ¯ β-Ga2O3 substrates, indicative ofsimilar dislocation densities for epilayers and substrates. Hence, hot-wall MOCVD is proposed as a prospective growth method to be furtherexplored for the fabrication of β-Ga2O3
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| 3. |
- Gogova, Daniela, 1967-, et al.
(author)
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Epitaxial growth of β-Ga2O3 by hot-wall MOCVD
- 2022
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In: AIP Advances. - : AIP Publishing. - 2158-3226. ; 12:5
-
Journal article (peer-reviewed)abstract
- The hot-wall metalorganic chemical vapor deposition (MOCVD) concept, previously shown to enable superior material quality and high performance devices based on wide bandgap semiconductors, such as Ga(Al)N and SiC, has been applied to the epitaxial growth of beta-Ga2O3. Epitaxial beta-Ga2O3 layers at high growth rates (above 1 mu m/h), at low reagent flows, and at reduced growth temperatures (740 degrees C) are demonstrated. A high crystalline quality epitaxial material on a c-plane sapphire substrate is attained as corroborated by a combination of x-ray diffraction, high-resolution scanning transmission electron microscopy, and spectroscopic ellipsometry measurements. The hot-wall MOCVD process is transferred to homoepitaxy, and single-crystalline homoepitaxial beta-Ga2O3 layers are demonstrated with a 201 rocking curve width of 118 arc sec, which is comparable to those of the edge-defined film-fed grown (201) beta-Ga2O3 substrates, indicative of similar dislocation densities for epilayers and substrates. Hence, hot-wall MOCVD is proposed as a prospective growth method to be further explored for the fabrication of beta-Ga2O3.
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| 4. |
- Knight, Sean Robert, et al.
(author)
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Room temperature two-dimensional electron gas scattering time, effective mass, and mobility parameters in AlxGa1−xN/GaN heterostructures (0.07 ≤ x ≤ 0.42)
- 2023
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In: Journal of Applied Physics. - : American Institute of Physics Inc.. - 0021-8979 .- 1089-7550. ; 134:18
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Journal article (peer-reviewed)abstract
- Al xGa 1−xN/GaN high-electron-mobility transistor (HEMT) structures are key components in electronic devices operating at gigahertz or higher frequencies. In order to optimize such HEMT structures, understanding their electronic response at high frequencies and room temperature is required. Here, we present a study of the room temperature free charge carrier properties of the two-dimensional electron gas (2DEG) in HEMT structures with varying Al content in the Al xGa 1−xN barrier layers between x=0.07 and x=0.42. We discuss and compare 2DEG sheet density, mobility, effective mass, sheet resistance, and scattering times, which are determined by theoretical calculations, contactless Hall effect, capacitance-voltage, Eddy current, and cavity-enhanced terahertz optical Hall effect (THz-OHE) measurements using a low-field permanent magnet (0.6 T). From our THz-OHE results, we observe that the measured mobility reduction from x=0.13 to x=0.42 is driven by the decrease in 2DEG scattering time, and not the change in effective mass. For x<0.42, the 2DEG effective mass is found to be larger than for electrons in bulk GaN, which in turn, contributes to a decrease in the principally achievable mobility. From our theoretical calculations, we find that values close to 0.3 m0 can be explained by the combined effects of conduction band nonparabolicity, polarons, and hybridization of the electron wavefunction through penetration into the barrier layer.
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| 5. |
- Persson, Ingemar, et al.
(author)
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Origin of layer decoupling in ordered multilayer graphene grown by high-temperature sublimation on C-face 4H-SiC
- 2020
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In: APL Materials. - : AMER INST PHYSICS. - 2166-532X. ; 8:1
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Journal article (peer-reviewed)abstract
- We study the origin of layer decoupling in ordered multilayer graphene grown by high temperature sublimation on C-face 4H-SiC. The mid-infrared optical Hall effect technique is used to determine the magnetic field dependence of the inter-Landau level transition energies and their optical polarization selection rules, which unambiguously show that the multilayer graphene consists of electronically decoupled layers. Transmission electron microscopy reveals no out-of-plane rotational disorder between layers in the stack, which is in contrast to what is typically observed for C-face graphene grown by low temperature sublimation. It is found that the multilayer graphene maintains AB-stacking order with increased interlayer spacing by 2.4%-8.4% as compared to highly oriented pyrolytic graphite. Electron energy loss spectroscopy mapping reveals Si atoms trapped in between layers, which are proposed to be the cause for the observed increased interlayer spacing leading to layer decoupling. Based on our results, we propose a defect-driven growth evolution mechanism for multilayer graphene on C-face SiC via high temperature sublimation.
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| 6. |
- Persson, Tomas, et al.
(author)
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Provningsmetod för sol- och biovärmesystem : Systemprestanda och emissionsdata
- 2012
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Reports (other academic/artistic)abstract
- SP i Borås och SERC, Högskolan Dalarna har i samverkan tagit fram en systemprovnings-metod där kompletta sol- och pelletsvärmesystem har provats i laboratorium under sex dygn. Plus två inledande dygn för termisk stabilisering av systemet. Provningen innefattar verklig-hetstrogna lastfall för två sommardagar, två vinterdagar, och två vår/höstdagar. Syftet är att få fram information om systemets helårsprestanda och systemfunktion genom en kortare tids provning. Vid mätningarna som genomförts vid Högskolan Dalarna har syftet också varit att undersöka systemens emissionsprestanda. Emissionsmätningarna ingår normalt inte i system-provningen, eftersom det skulle öka kostnaderna för att genomföra proven. Ett komplett system inklusive regulatorer provas med undantag för solfångaren, som utgörs av en dator-styrd rigg för att kunna skapa en repeterbar solvärmemängd från en systemspecifik solfångar-krets. Totalt har sju olika sol-pelletsystem provats samt ett referenssystem som utgörs av en kombi-panna utan solvärme. Dessutom har det inom projektet genomförts en jämförande provning mellan SP och Högskolan Dalarna på samma system. Provningsmetoden som utvecklats i detta projekt har visat sig kunna uppfylla målen, det vill säga kunna jämföra systemprestanda mellan olika system och uppskatta årsprestandan. Till detta har även eventuella driftsproblem i systemen kunnat identifieras så att dessa kan åtgärdas och systemen förbättras. För att förbättra provningsmetoden och öka noggrannheten i utvärderingen föreslås ett antal åtgärder inför en fortsatt provning. De viktigaste förändringarna är att se till att pannans och systemets laddstatus är så lika som möjligt vid början av sexdagarssekvensen, liksom vid sekvensens slut. Detta kräver två olika åtgärder: dels att de inledande två dygnen är identiska med de sista två dygnen och att panna triggas igång ett par timmar innan sekvensens början och slut, så att risken minskar att pannan levererar värme till tanken vid sekvensens början och slut. Vidare föreslås att en ny metod skall användas för att mäta värmeavgivningen till rummet från kaminer och att dess noggrannhet undersöks. För att åstadkomma exakt rätt last och solvärmetillskott vid provningen skall riggen använda en teknik med kontinuerlig kompensation av last och solvärmetillskott så att uppmätt och önskad energimängd alltid blir densamma i alla provningar. Detta förenklar även handhavan-det vid provningen och underlättar utvärderingen. För att kunna ge bättre återkoppling och kunna ge råd till hur systemen skall förbättras bör tanktemperaturen alltid mätas i några punk-ter och att förlustkoefficienter för panna och tank tas fram genom ett separat avsvalningsprov. Systemprovningen visar generellt att det är gynnsamt att kombinera pelleteldning med sol-värme. Pelletpannor har en låg verkningsgrad under låglastperioden och med solvärme kan pannan stängas av när driftsförutsättningarna är som sämst. Hög pannverkningsgrad liksom en väl fungerande ackumulatortank och styrsystem har visat sig vara avgörande för att erhålla höga systemprestanda i denna provningsmetod. Pannverk-ningsgraden över mätperioden är betydligt lägre än för motsvarande pannor under stationär drift på full effekt. Detta beror på att driftstiden för brännaren endast utgör en liten del av hela provningsperioden och därför blir pannans egenskaper under stilleståndsperioderna desto viktigare för systemets prestanda. Under stilleståndsperioderna är det värmeförlusterna till rummet som är avgörande för prestandan, medan värmeförlusterna har en försumbar inverkan på verkningsgraden när pannan eldas på full effekt enligt provningsmetoden för pannor EN 303-5. Resultaten pekar alltså på att de normala prestandaprovningarna för pannor enligt EN 303-5 inte ger någon garanti för att pannan är effektiv under verklighetstrogen drift och att provning vid stationär effekt inte heller styr utvecklingen mot bättre isolerade pannor och därmed effektivare sol- och biovärmesystem. Solfångarens prestanda och storlek har också relativt liten inverkan på den totala systempres-tandan. Solfångarprovning som garanterar solfångarens prestanda är viktigt för att garantera solfångarnas kvalitet och prestanda, men alltså inte på något sätt avgörande för att uppnå höga årsprestanda i kombinerade sol- och biobränslesystem Det finns uppenbarligen en stor förbätt-ringspotential för denna typ av system och den utvecklade provmetoden är ett mycket viktigt redskap för att effektivisera sol- och biovärmesystem. Emissionsfaktorer redovisade som medelvärde för hela provningssekvensen (sex dygn) var mellan 192 och 547 mg/MJ för CO, mellan 61 och 95 mg/MJ för NO, mellan 6 och 45 mg/MJ för TOC och mellan 31 och 116 mg/MJ för partiklar. För CO och NO ligger värdena inom de intervall som redovisas från forskningsprogrammet "biobränsle hälsa och miljö BHM. Upp-mätt medelkoncentration av kolväten och partiklar ligger betydligt högre än de emissionsfak-torer som redovisas av BHM. Andelen av emissionerna som släpps ut under start/stopp sekvenserna ligger mellan 63 och 96 % för CO-utsläppen och mellan 48 och 93 % av TOC-utsläppen. För partiklar är motsvarande andel mellan 30 och 39 % och för NO endast 10 till 21 %. Det betyder att styrningen av brän-naren och emissionskarakteristiken under start/stopp-blir mycket avgörande för hur mycket CO och TOC som släpps ut och att nuvarande metoder för miljömärkning av pelletpannor som baseras på stationära mätningar enligt EN 303-5 inte leder till att emissioner av CO och TOC minimeras på årsbasis.
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| 7. |
- Pettersson, Ulrik, et al.
(author)
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Provningsmetod för integrerade sol-biosystem : Årsverkningsgrad genom korttidsmätning
- 2011
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Reports (other academic/artistic)abstract
- Test method for integrated solar- biomass systems - Long term prediction trough short term measurements SP Technical Research Institute of Sweden and SERC, Dalarna University have in cooperation developed a test method for integrated solar and biomass systems. The test method is performed under six days including two summer days, two winter days and two spring/autumn days true to real weather conditions and loads for a single family house. The aim of the test method is to get information about a Combisystem’s annual performance and operation throughout a short term test. Seven different solar Combisystems have been tested within the project together with a pellet boiler without solar collectors. In addition to that a comparative testing has been performed at the two laboratories at SP and at SERC on the same Combisystem. The test method developed within the project has been proved to withstand the aim of the project, which is to be able to compare the performance between the systems. The test method is also suitable for identification of possible operation problems so they can be taken care of and consequently improves the system. The project and the system testing reveal that it is in general favorable to combine biomass pellets with solar heating. Pellet boilers has normally a low performance during the summer period but combined with a solar collector the boiler can be switch off during this period. There are however big differences in performance between the tested. The efficiency of the pellet boiler is highly dependent of the operating conditions and elements like heat losses from the system, system configuration and control strategy have great influence of the performance of the system and the emissions. On the other hand, the performance and the size of the solar collectors have a minor effect on the overall system performance. There is obviously a big potential for improvement of the system´s performance and the developed test method is an essential way to implement this perfection.
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| 8. |
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| 9. |
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| 10. |
- Andersson, Mathias H, et al.
(author)
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A framework for regulating underwater noise during pile driving
- 2017
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Reports (other academic/artistic)abstract
- Pile driving is a common technique used during the construction of bridges, offshore wind power, and underwater infrastructure or shoreline structures. It is the process by which a foundation, beam or pole is hammered or vibrated down into the bottom, which can generate extremely loud noise that propagates throughout the surrounding water and sediment. The noise can reach such high levels that marine animals are at risk of disturbance, injury or even death.Sweden currently lacks established thresholds stating the level at which underwater noise potentially disturbs or injures marine animals. Hence, there are no guidance values for allowable underwater noise levels from noiseproducing activities to avoid serious environmental impacts. Several countries in Europe have defined thresholds for when underwater noise can result in severe negative environmental impacts as well as standards for measuring, analysing and reporting underwater noise levels.The purpose of this study is to review the scientific literature on underwater noise from pile driving and its effects on marine life. The study aims to define the noise levels that can cause injury and other negative effects and, on this basis, recommend noise levels that can be used to establish guidance values for regulating underwater noise for Swedish waters and species. The study presents examples of the factors that contribute to sound propagation in Swedish waters and how this influences the noise level from a pile strike as a function of distance at four study areas along the Swedish coast. Additionally, the study contains a thorough technical description of pile driving activities, basic underwater acoustics and noise effects on marine animals. These effects (injury and behavioral, e.g., flight, but not subtle effects) are demonstrated on representative species such as the harbour porpoise (Phocoena phocoena), Atlantic cod (Gadus morhua), Atlantic herring (Clupea harengus) and on fish larvae and eggs. The study’s authors look atthe original sources of information that other countries base their guidelines and thresholds on, so the recommendations follow scientifically determined levels rather than values that have been rounded off or otherwise altered.The study presents sound levels in three different units, each with different biological relevance to the effects caused by a pile driving activity. None of the sound levels have been frequency weighted for a specific species, as this method is not yet fully established. The first unit used is the sound pressure level SPL(peak), which is the maximum overpressure or underpressure of the noise pulse generated by the pile strike. This unit has a high relevance for behavioural effects. The sound exposure level, SEL, is the calculated energy level over a period of time and expresses the energy of the entire sound pulse. SEL is the unit most related to hearing impairing effects. SEL(ss) is the value for a single strike while SEL(cum) is the cumulative value of a determined number of pulses over a period of time. The review revealed that for Atlantic cod and Atlantic herring there are currently no studies that can be used to determine a species’ specific threshold value for injury, but studies show that loud noise can affect both species negatively. Because of this, the recommended noise levels for injury are based mainly on studies on other species exposed to pile driving noise in laboratory environments, supported by studies conducting large-scale experiments in tanks and oceans. The levels at which fish are at risk of death or sustaining serious injury to internal organs is SPL 207 dB re 1 μPa, SEL(ss) 174 dB re 1 μPa2s and SEL(cum) 204 dB re 1 μPa2s. Note that for injury in fish, the cumulative sound exposure level has higher relevance than the single-strike level as the cited studies found injuries after a certain time period of exposure. The thresholds for fish larvae and eggs are based on the fact that no negative effects were observed at exposures of up to SPL(peak) 217 dB re 1 μPa, SEL(ss) 187 dB re 1 μPa2s and SEL(cum) 207 dB re 1 μPa2s. However, there are relatively few studies on early life stages of fish. There are more species-specific studies on harbour porpoises regarding noise than there are for Atlantic cod and Atlantic herring. Nonetheless, only a few can be used to determine thresholds that will lead to injury or negative behavioural effects. The levels at which there is a risk of a temporary impact on hearing, i.e. temporary threshold shift (TTS), for the harbour porpoises is SPL(peak) 194 dB re 1 μPa, SEL(ss) 164 dB re 1 μPa2s and SEL(cum) 175 dB re 1 μPa2s. When it comes to TTS, the cumulative sound exposure level, SEL(cum), is of primary importance. However, this unit is dependent on a specific time and number of pulses. For permanent threshold shift (PTS), the level is set to SPL(peak) 200 dB re 1 μPa, SEL(ss) 179 dB re 1 μPa2s and SEL(cum) 190 dB re 1 μPa2s. The recommended level should be revised as new relevant studies are conducted.
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| 11. |
- Andersson, Mathias H., et al.
(author)
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Displacement effects of ship noise on fish population : FP7 - Collaborative Project n° 314227 WP 4: Sensitivity of marine life to shipping noise Task 4.2.1
- 2015
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Reports (other academic/artistic)abstract
- Ship induced noise is one of the major contributors to the elevated noise levels in the world’s oceans today. However, the knowledge about the impact on marine organisms is still scarce. Especially the effects on fish behaviour needs to be studied as fish are a fundamental part of the oceans ecosystem. Direct measurement of fish behaviour in the open sea area is technically difficult but needs to be done in order to estimate reaction thresholds and scales of any reaction. This experiment studies the long term behavioural reaction by wild cod (Gadus morhua) to ship noise and describes the character and scale of the reaction. This study took place on the Swedish west coast with a small local cod population and the area is normally without any large vessel traffic. For the ship disturbance, the Swedish Coast Guard ship KBV 032 was hired and passed thru the area nine times during three days. During the three days of ship noise exposure, the noise levels increased well above the ambient noise. The ship signature was what could be expected in terms of spectral level with most radiated noise energy between 100 - 500 Hz. The ship had a higher source level than expected (232 dB re 1μPa at 1 m, 10 - 300 Hz) but this was deliberate as the crew was asked to use the propellers in a non-optimal way to generate as much noise as possible. The result was a lot of broadband cavitation pulses generated by the ship. Then a noise footprint model was created and used in the estimates of received levels (exposure level) by the individual fish in the area based on the most probable location. It was clear in the transmission loss varied between the two sites where at the shallow site, the noise was attenuated more compared to the deep site. This is probably caused by the quite complicated propagation pattern. Also, the acoustically different bottom properties will affect the transmission loss in the area. In total, 39 cod (Gadus morhua) were caught by hand jigging and were fitted with internal acoustical tags. Bottom mounted receivers were deployed covering the area where the cod were known to inhabit. This study was designed to capture more large scale movements of hundreds of meters and not startle responses to the ship noise. Out of the 39 tagged fish, 17 and 18 fish met the set quality criterion for the short time behaviour analysis and 23 fish for long time behaviour to be included in the analysis. Some fish met the quality criteria for both the short and long term analysis. The other fish were either eaten by seals, caught by fishermen, left the area or had a malfunctioning tag. In general, the noticed reaction in terms of horizontal swimming were much smaller than expected and what the study was designed for. This results was surprising as the sound pressure levels the fish were exposed to would, based on the literature, cause a strong behaviour response in the fish. The movement was not in any large scale that would affect their energy consumption and affect their long term survival. This study was able to track fish with an accuracy of less than 10 m and estimates an interval of received noise level. This is one of the first studies of its kind that is tracking free swimming fish over a long period of time during an acoustic disturbance.
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| 12. |
- Andersson, Mathias H., et al.
(author)
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Ljud från vindkraftverk i havet och dess påverkan på fisk
- 2011
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Reports (other academic/artistic)abstract
- Sedan lång tid tillbaka står den kommersiella fartygstrafiken för det största bidraget av antropogent ljud till den marina miljön. Konstruktion och drift av havsbaserad vindkraft gör att ytterliga ljud tillförs och än så länge vet vi lite om hur detta påverkar fisk. Denna studie syftar till att öka vår kunskap om vilken typ av ljud och vilka ljudnivåer som en vindkraftspark genererar under olika vindhastigheter. Ljudnivåer mellan enskilda turbiner och hela parken jämförs samt andra ljudkällor från Öresundsområdet som t.ex. fartyg. Vidare beskriver studien den potentiella påverkan på fisk som ljudet från en vindkraftpark kan ha. Studien är utförd i Öresund vid Lillgrunds vindkraftspark som byggdes 2007 och består av 48 turbiner (Siemens Mk II) med en individuell effekt av 2,3 MW. Parken ägs och drivs av Vattenfall. Två hydrofonsystem, ett batteridrivet och ett inkopplat på elnätet i en turbin, användes under den flera veckor långa mätperioden. Mätningar utfördes på olika avstånd till enskilda turbinerna liksom på längre avstånd från hela parken samt på ett kontrollområde (Sjollen) 10 km norr om parken. För att få en bättre förståelse av parkens bidrag till Öresunds ljudlandskap utvecklades en numerisk modell för parken där driftseffektivitet varieras. Vidare utvecklades en numerisk modell för det av fartyg utstrålande bullerbidraget för att jämföra fartygsgenererade ljudet från den närbelägna farleden Flintränna med vindkraftsparkens ljud.Resultaten visar att vindkraftverken producerar ett bredbandigt ljud under 1 kHz samt ett par toner där 127 Hz tonen är den kraftigaste. Den maximala beräknade ljudnivåerna som vindkraftverken genererar var 136 och 138 dB re 1μPa(RMS) vid en meter vid full effekt (12 m/s) för den av turbinerna dominanta 127 Hz (integrerad över 123-132 Hz) tonen respektive vid fullt spektrum (integrerad över 52-343 Hz). Denna ljudnivå ligger mellan 33-55 dB över bakgrundsnivån. På ett avstånd av 100 m från en turbin har ljudnivåerna gått ner till 104-106 dB re 1μPa(RMS) vilket är nära det lokalt uppmätta bredbandiga bakgrundsljudet, men ljudnivån ligger fortfarande omkring 23 dB över bakgrunden för 127 Hz tonen.Denna studie är vad man vet den första som påvisar en parkeffekt där varje enskild turbin ökar ljudnivån i området. På längre avstånd än 80 meter från en turbin kommer ljudnivån att få ett ej försumbart bidrag från närliggande turbiner. Ljudets utbredning beräknades att minska med 17×log (avståndet) på nära håll (80 m) och vid avstånd större än sju kilometer. På grund av att den mesta av ljudenergin är fokuserad till 127 Hz tonen kommer ljudet att skära igenom det fartygsdominerade ljudlandskapet och på så sätt blir hörbart för fisk på längre avstånd än vad annars skulle vara fallet.De uppmätta och beräknade ljudnivåerna vid Lillgrunds vindkraftspark har i andra studier inte gett några fysiska skador på fisk. Det är endast inom ca 100 meter från en turbin och vid höga vindstyrkor som nivåerna är tillräckligt höga för att det finns risk att fisk påverkas negativt i form av flyktbeteende eller möjlig maskering av kommunikation. För lax och ål blev detektionsavståndet för 127 Hz tonen 250 meter respektive en kilometer för en driftseffektivitet på 60 och 100 %, vilket motsvarar vindstyrkorna på ca 6 och 12 m/s. Dessa beräknade avstånden begränsas av arternas hörselförmåga. För sill och torsk däremot är deras detektionsavstånd av vindkraftsljudet begränsat av bakgrundsbruset och är då beräknat till mellan 13 och 16 kilometer. Detta är ett långt avstånd och är beräknad med den uppmätta utbredningsförlusten som gäller i vindkraftsområdet. Men lokala variationer av bottendjup och fysiska hinder som t.ex. halvön Falsterbonäset ändrar förutsättningarna för ljudutbredningen och som resultat gäller inte antagandet för ljudutbredningen för större avstånd från parken. Som exempel detekterades inte 127 Hz tonen i inspelningarna vid Sjollen som ligger 10 kilometer norr om vindkraftparken. I dagsläget finns det inget som tyder på att bara för att ljudet är hörbart skulle det vara förenat med några negativa konsekvenser för fiskarna på populationsnivå.
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| 13. |
- Andersson, Mathias H., et al.
(author)
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Underlag för reglering av undervattensljud vid pålning
- 2016
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Reports (other academic/artistic)abstract
- Vid byggnation av broar, havsbaserad vindkraft och andra havsbaserade eller strandnära konstruktioner används det oftast någon form av pålningsteknik för att få ner konstruktionen i botten. Detta innebär att ett fundament, balk eller spont hamras eller vibreras ner i botten, vilket kan generera mycket höga ljudnivåer som sprids ut i vattnet och ner i botten. Ljudnivåerna är så höga att marina organismer kan störas, skadas eller till och med dödas. Idag saknar Sverige fastställda ljudnivåer för när undervattensbuller blir så högt att de kan skada djur i havet. Det saknas därför också vedertagna begränsningsvärden som anger vilka nivåer av undervattensbuller som kan tillåtas för bullrande aktiviteter utan att riskera allvarliga miljöeffekter. Flera länder i Europa har någon form av gränsvärden för när bullernivån under vattnet kan ge upphov till allvarlig miljöpåverkan liksom standarder för hur undervattensbuller skall mätas och rapporteras. Syftet med denna studie var att ta fram ett vetenskapligt underlag rörande ljudet från pålning i havet och dess påverkan på det marina livet. Slutmålet var att utifrån den vetenskapliga information som finns idag ge förslag på ljudnivåer för skador och negativ påverkan som sedan kan användas för att ta fram begränsningsvärden för reglering av undervattensbuller anpassade för svenska vatten och arter. Studien ger ett antal exempel på vilka faktorer som påverkar ljudutbredningen i svenska vatten och hur detta påverkar ett pålningsslags ljudnivå som funktion av avstånd i fyra typområden kring den svenska kusten. Vidare presenteras ingående både tekniska beskrivningar av pålningsaktiviteter, undervattensakustik samt påverkan på marina djur. Denna påverkan (skada och flyktbeteende men ej subtila effekter) demonstreras med hjälp av ett antal typarter som tandvalen tumlare (Phocoena phocoena) och fiskarterna torsk (Gadus morhua) och sill (Clupea clupea) samt fiskägg och fisklarver. I denna studie har författarna gått tillbaka till de originalkällor av information som andra länders gränsvärden grundas på, så att rekommendationerna bygger på vetenskapliga nivåer och inte värden som har avrundats eller på annat sätt ändrats.Studien presenterar ljudnivåer i tre olika enheter då dessa har olika biologisk relevans för påverkan från en pålningsaktivitet. Inga av dessa värden har frekvensviktats för att anpassas för en specifik art då denna metod ännu inte är helt vedertagen. Den första enheten är ljudtrycksnivå SPL(topp), d.v.s. det maximala över- eller undertryck som den av pålningsslaget genererade ljudpulsen har. Denna enhet har hög relevans för beteendepåverkan. För ljudexponeringsnivå SEL, beräknas ljudnivån över en viss tid och tar då med energin i hela ljudpulsen. SEL är den enhet som visats vara bäst relaterad till hörselskador. SEL(enkel) är värdet för en enkel puls och för det kumulativa SEL(kum) har antalet pulser under en viss tid summerats.Litteraturstudien på torsk och sill visar att det i dagsläget inte finns några studier som kan användas för att fastställa en artspecifik ljudnivå för skada men litteraturen visar tydligt på att höga bullernivåer kan påverka torsk och sill negativt. Istället baseras de föreslagna nivåerna i huvudsak på studier på andra arter som har exponerats för pålningsljud i laboratoriemiljö med stöd av studier från mer storskaliga experiment i tankar och hav. De nivåer då fisk riskerar att dödas eller få allvarliga skador på inre organ är 207 dB re 1 μPa SPL(topp), 174 dB re 1 μPa2s SEL(enkel) och 204 dB re 1 μPa2s SEL(kum). Notera att för skada på fisk har det kumulativa värdet högre relevans än enkelvärdet för SEL eftersom studier visar att skador uppkommer efter en viss tids exponering. Nivåerna för påverkan på fiskägg och larver grundas i att inga negativa effekter har observerats vid exponering för ljudtryck från pålning upp till 217 dB re 1 μPa SPL(topp), 187 dB re 1 μPa2s SEL(enkel) och 207 dB re 1 μPa2s SEL(kum). Det finns emellertid mycket få studier relaterat till pålningsljud för dessa livsstadier. För tumlare finns det fler artspecifika studier gjorda relaterat till buller än för torsk och sill. Det är dock endast ett fåtal som kan användas för att bestämma ljudnivåer som leder till skada eller negativ beteendepåverkan. De ljudnivåer som riskerar ge tillfällig hörselnedsättning (TTS) hos tumlare är 194 dB re 1 μPa SPL(topp), 164 dB re 1 μPa2s SEL(enkel) och 175 dB re 1 μPa2s SEL(kum). Det är framförallt den kumulativa ljudexponeringsnivån SEL(kum) som har stor betydelse för just TTS, dock hänger detta värde ihop med en specifik tid och antalet pulser vilket kan vara svårt att uppskatta i förväg. Vidare avseende permanent hörselskada (PTS) är ljudnivån 200 dB re 1 μPa SPL(topp), 179 dB re 1 μPa2s SEL(enkel) och 190 dB re 1 μPa2s SEL(kum). Föreslagna nivåer bör uppdateras när nya relevanta forskningsstudier tillkommer.
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| 14. |
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| 15. |
- Asplund, C., et al.
(author)
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Real-time RT-PCR of protein epitope signature tags
- 2005
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In: Molecular & Cellular Proteomics. - : AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC. - 1535-9476 .- 1535-9484. ; 4:8, s. S60-S60
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Journal article (other academic/artistic)
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| 16. |
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| 17. |
- Barroso da Silva, Fernando Luis, et al.
(author)
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Effect of Charge Regulation and Ion-Dipole Interactions on the Selectivity of Protein-Nanoparticle Binding
- 2014
-
In: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 30:14, s. 4078-4083
-
Journal article (peer-reviewed)abstract
- We investigate the role of different mesoscopic interactions (Coulomb, charge regulation, and ion-dipole "surface patch" effects) on the binding of bovine serum albumin (BSA) and beta-lactoglobulin (BLG) to a cationic gold nanoparticle (TTMA+). The results demonstrate that the charge-regulation mechanism plays a vital role for selectivity of protein-nanoparticle complexation at low salt concentration. At slightly higher ionic strengths, charge-dipole effects are the dominating driving force. Thus, very small variations in salt concentration strongly influence the origin of complexation.
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| 18. |
- Berglund, Lisa, et al.
(author)
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A genecentric Human Protein Atlas for expression profiles based on antibodies
- 2008
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In: Molecular & Cellular Proteomics. - 1535-9476 .- 1535-9484. ; 7:10, s. 2019-2027
-
Research review (peer-reviewed)abstract
- An attractive path forward in proteomics is to experimentally annotate the human protein complement of the genome in a genecentric manner. Using antibodies, it might be possible to design protein-specific probes for a representative protein from every protein-coding gene and to subsequently use the antibodies for systematical analysis of cellular distribution and subcellular localization of proteins in normal and disease tissues. A new version (4.0) of the Human Protein Atlas has been developed in a genecentric manner with the inclusion of all human genes and splice variants predicted from genome efforts together with a visualization of each protein with characteristics such as predicted membrane regions, signal peptide, and protein domains and new plots showing the uniqueness (sequence similarity) of every fraction of each protein toward all other human proteins. The new version is based on tissue profiles generated from 6120 antibodies with more than five million immunohistochemistry-based images covering 5067 human genes, corresponding to approximately 25% of the human genome. Version 4.0 includes a putative list of members in various protein classes, both functional classes, such as kinases, transcription factors, G-protein-coupled receptors, etc., and project-related classes, such as candidate genes for cancer or cardiovascular diseases. The exact antigen sequence for the internally generated antibodies has also been released together with a visualization of the application-specific validation performed for each antibody, including a protein array assay, Western blot analysis, immunohistochemistry, and, for a large fraction, immunofluorescence-based confocal microscopy. New search functionalities have been added to allow complex queries regarding protein expression profiles, protein classes, and chromosome location. The new version of the protein atlas thus is a resource for many areas of biomedical research, including protein science and biomarker discovery.
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| 19. |
- Berglund, Lisa, et al.
(author)
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Generation of validated antibodies towards the human proteome
-
Journal article (other academic/artistic)abstract
- Here we show the results from a large effort to generate antibodies towards the human proteome. A high-throughput strategy was developed based on cloning and expression of antigens as recombitant protein epitope signature tags (PrESTs) Affinity purified polyclonal antibodies were generated, followed by validation by protein microarrays, Western blotting and microarray-based immunohistochemistry. PrESTs were selected based on sequence uniqueness relative the proteome and a bioinformatics analysis showed that unique antigens can be found for at least 85% of the proteome using this general strategy. The success rate from antigen selection to validated antibodies was 31%, and from protein to antibody 55%. Interestingly, membrane-bound and soluble proteins performed equally and PrEST lengths between 75 and 125 amino acids were found to give the highest yield of validated antibodies. Multiple antigens were selected for many genes and the results suggest that specific antibodies can be systematically generated to most human proteibs.
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| 20. |
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| 21. |
- Berglund, Martin, 1985-, et al.
(author)
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Evaluation of a microplasma source based on a stripline split-ring resonator
- 2013
-
In: Plasma sources science & technology. - : Institute of Physics (IOP). - 0963-0252 .- 1361-6595. ; 22:5, s. 055017-
-
Journal article (peer-reviewed)abstract
- In this paper, a stripline split-ring resonator microwave-induced plasma source, aimed for integration in complex systems, is presented and compared with a traditional microstrip design. Devices based on the two designs are evaluated using a plasma breakdown test setup for measuring the power required to ignite plasmas at different pressures. Moreover, the radiation efficiency of the devices is investigated with a Wheeler cap, and their electromagnetic compatibility is investigated in a variable electrical environment emulating an application. Finally, the basic properties of the plasma in the two designs are investigated in terms of electron temperature, plasma potential and ion density. The study shows that, with a minor increase in plasma ignition power, the stripline design provides a more isolated and easy-to-integrate alternative to the conventional microstrip design. Moreover, the stripline devices showed a decreased antenna efficiency as compared with their microstrip counterparts, which is beneficial for plasma sources. Furthermore, the investigated stripline devices exhibited virtually no frequency shift in a varying electromagnetic environment, whereas the resonance frequency of their microstrip counterparts shifted up to 17.5%. With regard to the plasma parameters, the different designs showed only minor differences in electron temperature, whereas the ion density was higher with the stripline design.
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| 22. |
- Bostrom, Mathias, et al.
(author)
-
Lifshitz interaction can promote ice growth at water-silica interfaces
- 2017
-
In: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 95:15
-
Journal article (peer-reviewed)abstract
- At air-water interfaces, the Lifshitz interaction by itself does not promote ice growth. On the contrary, we find that the Lifshitz force promotes the growth of an ice film, up to 1-8 nm thickness, near silica-water interfaces at the triple point of water. This is achieved in a system where the combined effect of the retardation and the zero frequency mode influences the short-range interactions at low temperatures, contrary to common understanding. Cancellation between the positive and negative contributions in the Lifshitz spectral function is reversed in silica with high porosity. Our results provide a model for how water freezes on glass and other surfaces.
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| 23. |
- Bostrom, Mathias, et al.
(author)
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Self-preserving ice layers on CO2 clathrate particles : Implications for Enceladus, Pluto, and similar ocean worlds
- 2021
-
In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 650
-
Journal article (peer-reviewed)abstract
- Context. Gas hydrates can be stabilised outside their window of thermodynamic stability by the formation of an ice layer - a phenomenon termed self-preservation. This can lead to a positive buoyancy for clathrate particles containing CO2 that would otherwise sink in the oceans of Enceladus, Pluto, and similar oceanic worlds.Aims. Here we investigate the implications of Lifshitz forces and low occupancy surface regions on type I clathrate structures for their self-preservation through ice layer formation, presenting a plausible model based on multi-layer interactions through dispersion forces.Methods. We used optical data and theoretical models for the dielectric response for water, ice, and gas hydrates with a different occupancy. Taking this together with the thermodynamic Lifshitz free energy, we modelled the energy minima essential for the formation of ice layers at the interface between gas hydrate and liquid water.Results. We predict the growth of an ice layer between 0.01 and 0.2 mu m thick on CO, CH4, and CO2 hydrate surfaces, depending on the presence of surface regions depleted in gas molecules. Effective hydrate particle density is estimated, delimiting a range of particle size and compositions that would be buoyant in different oceans. Over geological time, the deposition of floating hydrate particles could result in the accumulation of kilometre-thick gas hydrate layers above liquid water reservoirs and below the water ice crusts of their respective ocean worlds. On Enceladus, the destabilisation of near-surface hydrate deposits could lead to increased gas pressures that both drive plumes and entrain stabilised hydrate particles. Furthermore, on ocean worlds, such as Enceladus and particularly Pluto, the accumulation of thick CO2 or mixed gas hydrate deposits could insulate its ocean against freezing. In preventing freezing of liquid water reservoirs in ocean worlds, the presence of CO2-containing hydrate layers could enhance the habitability of ocean worlds in our Solar System and on the exoplanets and exomoons beyond.
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| 24. |
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| 25. |
- Boström, Mathias, et al.
(author)
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Atmospheric water droplets can catalyse atom pair break-up via surface-induced resonance repulsion
- 2013
-
In: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 101:4, s. 43002-
-
Journal article (peer-reviewed)abstract
- We present the theory for a retarded resonance interaction between two identical atoms near a dielectric surface. In free space the resonance interaction between isotropically excited atom pairs is attractive at all atom-atom separations. We illustrate numerically how this interaction between oxygen, sulphur, hydrogen, or nitrogen atom pairs may turn repulsive near water droplets. The results provide evidence of a mechanism causing excited state atom pair breakage to occur in the atmosphere near water droplets.
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| 26. |
- Boström, Mathias, et al.
(author)
-
Casimir attractive-repulsive transition in MEMS
- 2012
-
In: European Physical Journal B. - : Springer Science and Business Media LLC. - 1434-6028 .- 1434-6036. ; 85:11, s. 377-
-
Journal article (peer-reviewed)abstract
- Unwanted stiction in micro-and nanomechanical (NEMS/MEMS) systems due to dispersion (van der Waals, or Casimir) forces is a significant hurdle in the fabrication of systems with moving parts on these length scales. Introducing a suitably dielectric liquid in the interspace between bodies has previously been demonstrated to render dispersion forces repulsive, or even to switch sign as a function of separation. Making use of recently available permittivity data calculated by us we show that such a remarkable nonmonotonic Casimir force, changing from attractive to repulsive as separation increases, can in fact be observed in systems where constituent materials are in standard NEMS/MEMS use requiring no special or exotic materials. No such nonmonotonic behaviour has been measured to date. We calculate the force between a silica sphere and a flat surface of either zinc oxide or hafnia, two materials which are among the most prominent for practical microelectrical and microoptical devices. Our results explicate the need for highly accurate permittivity functions of the materials involved for frequencies from optical to far-infrared frequencies. A careful analysis of the Casimir interaction is presented, and we show how the change in the sign of the interaction can be understood as a result of multiple crossings of the dielectric functions of the three media involved in a given set-up.
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| 27. |
- Boström, Mathias, et al.
(author)
-
Casimir force between atomically thin gold films
- 2013
-
In: European Physical Journal B. - : Springer Science and Business Media LLC. - 1434-6028 .- 1434-6036. ; 86:2, s. 43-
-
Journal article (peer-reviewed)abstract
- We have used density functional theory to calculate the anisotropic dielectric functions for ultrathin gold sheets (composed of 1, 3, 6, and 15 atomic layers). Such films are important components in nano-electromechanical systems. When using correct dielectric functions rather than bulk gold dielectric functions we predict an enhanced attractive Casimir-Lifshitz force (at most around 20%) between two atomically thin gold sheets. For thicker sheets the dielectric properties and the corresponding Casimir forces approach those of gold half-spaces. The magnitude of the corrections that we predict should, within the today's level of accuracy in Casimir force measurements, be clearly detectable.
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| 28. |
- Boström, Mathias, et al.
(author)
-
Casimir-Lifshitz interaction between ZnO and SiO2 nanorods in bromobenzene turns repulsive at intermediate separations due to retardation effects
- 2012
-
In: Physical Review A. Atomic, Molecular, and Optical Physics. - : American Physical Society. - 1050-2947 .- 1094-1622. ; 85:4, s. 044702-
-
Journal article (peer-reviewed)abstract
- We consider the interaction between a ZnO nanorod and a SiO2 nanorod in bromobenzene. Using optical data for the interacting objects and ambient we calculate the force (from short-range attractive van der Waals force to intermediate-range repulsive Casimir-Lifshitz force to long-range entropically driven attraction). The nonretarded van der Waals interaction is attractive at all separations. We demonstrate a retardation-driven repulsion at intermediate separations. At short separations (in the nonretarded limit) and at large separations (in the classical limit) the interaction is attractive. These effects can be understood from an analysis of multiple crossings of the dielectric functions of the three media as functions of imaginary frequencies.
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| 29. |
- Boström, Mathias, et al.
(author)
-
Enlarged molecules from excited atoms in nanochannels
- 2012
-
In: Physical Review A. Atomic, Molecular, and Optical Physics. - : American Physical Society. - 1050-2947 .- 1094-1622. ; 86:1, s. 014701-
-
Journal article (peer-reviewed)abstract
- The resonance interaction that takes place in planar nanochannels between pairs of excited-state atoms is explored. We consider interactions in channels of silica, zinc oxide, and gold. The nanosized channels induce a dramatically different interaction from that in free space. Illustrative calculations for two lithium and cesium atoms demonstrate that there is a short-range repulsion followed by long-range attraction. The binding energy is strongest near the surfaces. The size of the enlarged molecule is biggest at the center of the cavity and increases with channel width. Since the interaction is generic, we predict that enlarged molecules are formed in porous structures, and that the molecule size depends on the size of the nanochannels.
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| 30. |
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| 31. |
- Boström, Mathias, et al.
(author)
-
Increased porosity turns desorption to adsorption for gas bubbles near water-SiO2 interface
- 2015
-
In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 91:7
-
Journal article (peer-reviewed)abstract
- We consider theoretically the retarded van der Waals interaction of a small gas bubble in water with a porous SiO2 surface. We predict a possible transition from repulsion to attraction as the surface is made more porous. It highlights that bubbles will interact differently with surface regions with different porosity (i.e., with different optical properties).
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| 32. |
- Boström, Mathias, et al.
(author)
-
Lithium atom storage in nanoporous cellulose via surface-induced Li-2 breakage
- 2013
-
In: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 104:6, s. 63003-
-
Journal article (peer-reviewed)abstract
- We demonstrate a physical mechanism that enhances a splitting of diatomic Li-2 at cellulose surfaces. The origin of this splitting is a possible surface-induced diatomic-excited-state resonance repulsion. The atomic Li is then free to form either physical or chemical bonds with the cellulose surface and even diffuse into the cellulose layer structure. This allows for an enhanced storage capacity of atomic Li in nanoporous cellulose.
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| 33. |
- Boström, Mathias, et al.
(author)
-
Resonance interaction induced by metal surfaces catalyzes atom-pair breakage
- 2013
-
In: Physical Review A. Atomic, Molecular, and Optical Physics. - : American Physical Society. - 1050-2947 .- 1094-1622. ; 87:4, s. 044701-
-
Journal article (peer-reviewed)abstract
- We present the theory for retarded resonance interaction between two identical atoms at arbitrary positions near a metal surface. The dipole-dipole resonance interaction force that binds isotropically excited atom pairs together in free space may turn repulsive close to an ideal (totally reflecting) metal surface. On the other hand, close to an infinitely permeable surface it may turn more attractive. We illustrate numerically how the dipole-dipole resonance interaction between two oxygen atoms near a metal surface may provide a repulsive energy of the same order of magnitude as the ground-state binding energy of an oxygen molecule. As a complement we also present results from density-functional theory.
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| 34. |
- Boström, Mathias, et al.
(author)
-
Ultrathin metallic coatings can induce quantum levitation between nanosurfaces
- 2012
-
In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 100:25, s. 253104-
-
Journal article (peer-reviewed)abstract
- There is an attractive Casimir-Lifshitz force between two silica surfaces in a liquid (bromobenze or toluene). We demonstrate that adding an ultrathin (5-50 angstrom) metallic nanocoating to one of the surfaces results in repulsive Casimir-Lifshitz forces above a critical separation. The onset of such quantum levitation comes at decreasing separations as the film thickness decreases. Remarkably, the effect of retardation can turn attraction into repulsion. From that we explain how an ultrathin metallic coating may prevent nanoelectromechanical systems from crashing together.
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| 35. |
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| 36. |
- Broth, Mathias, 1965-, et al.
(author)
-
Inspelning och analys av interaktionsdata
- 2020
-
In: Multimodal interaktionsanalys. - Lund : Studentlitteratur AB. - 9789144127521 ; , s. 41-74
-
Book chapter (other academic/artistic)abstract
- Inom multimodal interaktionsanalys utgörs data av videoinspelningar. Utan en videoinspelning kan man inte utföra multimodal interaktionsanalys i enlighet med vad som avses i denna bok. Videoanalysen inbegriper generellt såväl identifiering av relevanta sekvenser i förhållande till ett visst forskningsintresse som transkription av vad som dokumenterats i videofilmen och framskrivande av en empiriskt grundad argumentation. Det är denna analysprocess, ”från ax till limpa”, som utgör ämnet för detta kapitel. Olika undersökningar kan naturligtvis se olika ut. Vår framställning kan därför ses som ett vägledande förslag på arbetsgång.
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| 37. |
- Broth, Mathias, et al.
(author)
-
Inspelning och analys av interaktionsdata
- 2020. - 1
-
In: Multimodal interaktionsanalys. - : Studentlitteratur AB. - 9789144127521 ; , s. 41-74
-
Book chapter (other academic/artistic)
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| 38. |
- Browne, Katherine, et al.
(author)
-
How does policy coherence shape effectiveness and inequality? Implications for sustainable development and the 2030 Agenda
- 2023
-
In: Sustainable Development. - : Wiley-Blackwell. - 0968-0802 .- 1099-1719. ; 31:5, s. 3161-3174
-
Journal article (peer-reviewed)abstract
- During the formulation of the 2030 Agenda for Sustainable Development, many promoted policy coherence as a key tool to ensure achievement of the Sustainable Development Goals (SDGs) in a way that “leaves no one behind.” Their argument assumed that coherent policymaking contributes to more effective policies and supports over-arching efforts to reduce inequality. As the 2030 Agenda reaches the halfway point, however, countries are falling short on many SDGs, particularly SDG 10 (reduce inequality). This study revisits the basic assumptions about policy coherence underpinning the SDGs. We systematically screened the peer-reviewed literature to identify 40 studies that provide evidence about whether coherent policymaking contributes to more effective outcomes and helps to reduce inequality. We find that coherent policymaking did not help reduce inequality in a majority of cases and made it worse in several. Our findings challenge the narrative that coherence is a necessary pre-condition for progress on the SDGs for all people.
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| 39. |
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| 40. |
- Cöster, Mathias, 1969-, et al.
(author)
-
Enabling sustainable visits : Introduction
- 2023
-
In: Enabling Sustainable Visits. - Visby : Uppsala University. - 9789150630145 - 9789150630237
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Book chapter (other academic/artistic)
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| 41. |
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| 42. |
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| 43. |
- Dou, Maofeng, et al.
(author)
-
Casimir quantum levitation tuned by means of material properties and geometries
- 2014
-
In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 89:20, s. 201407-
-
Journal article (peer-reviewed)abstract
- The Casimir force between two surfaces is attractive in most cases. Although stable suspension of nano-objects has been achieved, the sophisticated geometries make them difficult to be merged with well-established thin film processes. We find that by introducing thin film surface coating on porous substrates, a repulsive to attractive force transition is achieved when the separations are increased in planar geometries, resulting in a stable suspension of two surfaces near the force transition separation. Both the magnitude of the force and the transition distance can be flexibly tailored though modifying the properties of the considered materials, that is, thin film thickness, doping concentration, and porosity. This stable suspension can be used to design new nanodevices with ultralow friction. Moreover, it might be convenient to merge this thin film coating approach with micro- and nanofabrication processes in the future.
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| 44. |
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| 45. |
- Fiedler, Johannes, et al.
(author)
-
Dispersion forces in inhomogeneous planarly layered media : A one-dimensional model for effective polarizabilities
- 2019
-
In: Physical Review A. - 2469-9926. ; 99:6
-
Journal article (peer-reviewed)abstract
- Dispersion forces such as van der Waals forces between two microscopic particles, the Casimir-Polder forces between a particle and a macroscopic object, or the Casimir force between two dielectric objects are well studied in vacuum. However, in realistic situations the interacting objects are often embedded in an environmental medium. Such a solvent influences the induced dipole interaction. With the framework of macroscopic quantum electrodynamics, these interactions are mediated via an exchange of virtual photons. Via this method the impact of a homogeneous solvent medium can be expressed as local-field corrections leading to excess polarizabilities which have previously been derived for hard boundary conditions. In order to develop a more realistic description, we investigate a one-dimensional analog system illustrating the influence of a continuous dielectric profile.
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| 46. |
- Fiedler, Johannes, et al.
(author)
-
Effective Polarizability Models
- 2017
-
In: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 121:51, s. 9742-9751
-
Journal article (peer-reviewed)abstract
- Theories for the effective polarizability of a small particle in a medium are presented using different levels of approximation: we consider the virtual cavity, real cavity, and the hard-sphere models as well as a continuous interpolation of the latter two. We present the respective hard-sphere and-cavity radii as obtained from density-functional simulations as well as the resulting effective polarizabilities at discrete Matsubara frequencies. This enables us to account for macroscopic media in van der Waals interactions between molecules in water and their Casimir-Polder interaction with an interface.
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| 47. |
- Fiedler, Johannes, et al.
(author)
-
Full-Spectrum High-Resolution Modeling of the Dielectric Function of Water
- 2020
-
In: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 124:15, s. 3103-3113
-
Journal article (peer-reviewed)abstract
- In view of the vital role of water, exact knowledge of its dielectric function over a large frequency range is important. We report on currently available measurements of the dielectric function of water at room temperature (25 degrees C) across the full spectrum: microwave, IR, UV, and X-ray (up to 100 eV). We parameterize the complex dielectric function of water with two Debye (microwave) oscillators and high resolution of IR and UV/X-ray oscillators. We also report dielectric parameters for ice-cold water with a microwave/IR spectrum measured at 0.4 degrees C, while taking the UV spectrum at 25 degrees C (assuming negligible temperature dependence in UV). We employ van der Waals dispersion interactions to contrast our model of ice-cold water with earlier models. Air bubbles in water and dissolved gas molecules show attraction toward interfaces rather than repulsion. The van der Waals interaction promotes complete freezing rather than supporting a thin layer of water on ice. We infer that premelting is driven by charge and ion adsorption. Density-based extrapolation from warm to cold water of the dielectric function is satisfactory in microwave but poor (40% error) at IR frequencies.
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| 48. |
- Fiedler, Johannes, et al.
(author)
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Impact of effective polarisability models on the near-field interaction of dissolved greenhouse gases at ice and air interfaces
- 2019
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In: Physical chemistry chemical physics : PCCP. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 21:38, s. 21296-21304
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Journal article (peer-reviewed)abstract
- We present a theory for Casimir-Polder forces acting on greenhouse gas molecules dissolved in a thin water film. Such a nano-sized film has been predicted to arise on the surface of melting ice as stabilized by repulsive Lifshitz forces. We show that different models for the effective polarisability of greenhouse gas molecules in water lead to different predictions for how Casimir-Polder forces influence their extractions from the melting ice surface. For instance, in the most intricate model of a finite-sized molecule inside a cavity, dispersion potentials push the methane molecules towards the ice surface whereas the oxygen typically will be attracted towards the closest interface (ice or air). Previous models for effective polarisability had suggested that O2 would also be pushed towards the ice surface. Release of greenhouse gas molecules from the surface of melting ice can potentially influence climate greenhouse effects. With this model, we show that some molecules cannot escape from water as single molecules. Due to the contradiction of the results and the escape dynamics of gases from water, we extended the models to describe bubble filled with several molecules increasing their buoyancy force.
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| 49. |
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| 50. |
- Hamsten, Carl, 1981-, et al.
(author)
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Expression and immunogenicity of six putative variable surface proteins in Mycoplasma mycoides subsp. mycoides SC.
- 2008
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In: Microbiology. - Reading : Society for General Microbiology. - 1350-0872 .- 1465-2080. ; 154, s. 539-549
-
Journal article (peer-reviewed)abstract
- Variable surface protein Vmm and five Vmm-type proteins from Mycoplasma mycoides subsp. mycoides SC were analysed to determine whether these proteins are expressed in vivo in animals affected by contagious bovine pleuropneumonia (CBPP) and in vitro. Recombinant versions of these proteins were constructed and expressed in Escherichia coli after mutation of the TGA Trp codons to TGG. These proteins were then analysed by dot and Western blotting with sera from CBPP-affected cattle. Furthermore, affinity-purified polyclonal antibodies to the recombinant proteins were used in Western and colony blotting to look for expression of the putative Vmm-type proteins in cultured M. mycoides SC. This study demonstrates that immunoglobulins in CBPP sera recognize all putative Vmm-type proteins tested, indicating that these proteins or their homologues are expressed by mycoplasmas during natural infections. Vmm and one of the putative Vmm-type proteins showed variable expression in vitro.
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