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| 2. |
- Zinke, Julika, et al.
(författare)
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The development of a miniaturised balloon-borne cloud water sampler and its first deployment in the high Arctic
- 2021
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Ingår i: Tellus. Series B, Chemical and physical meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 73:1, s. 1-12
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Tidskriftsartikel (refereegranskat)abstract
- The chemical composition of cloud water can be used to infer the sources of particles upon which cloud droplets and ice crystals have formed. In order to obtain cloud water for analysis of chemical composition for elevated clouds in the pristine high Arctic, balloon-borne active cloud water sampling systems are the optimal approach. However, such systems have not been feasible to deploy previously due to their weight and the challenging environmental conditions. We have taken advantage of recent developments in battery technology to develop a miniaturised cloud water sampler for balloon-borne collection of cloud water. Our sampler is a bulk sampler with a cloud drop cutoff diameter of approximately 8 mu m and an estimated collection efficiency of 70%. The sampler was heated to prevent excessive ice accumulation and was able to operate for several hours under the extreme conditions encountered in the high Arctic. We have tested and deployed the new sampler on a tethered balloon during the Microbiology-Ocean-Cloud-Coupling in the High Arctic (MOCCHA) campaign in August and September 2018 close to the North pole. The sampler was able to successfully retrieve cloud water samples that were analysed to determine their chemical composition as well as their ice-nucleating activity. Given the pristine conditions found in the high Arctic we have placed significant emphasis on the development of a suitable cleaning procedure to minimise background contamination by the sampler itself.
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| 3. |
- Akbari, Saeed, et al.
(författare)
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Ceramic Additive Manufacturing Potential for Power Electronics Packaging
- 2022
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Ingår i: IEEE Transactions on Components, Packaging, and Manufacturing Technology. - : Institute of Electrical and Electronics Engineers Inc.. - 2156-3950 .- 2156-3985. ; 12:11, s. 1857-1866
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Tidskriftsartikel (refereegranskat)abstract
- Compared with silicon-based power devices, wide band gap (WBG) semiconductor devices operate at significantly higher power densities required in applications such as electric vehicles and more electric airplanes. This necessitates development of power electronics packages with enhanced thermal characteristics that fulfil the electrical insulation requirements. The present research investigates the feasibility of using ceramic additive manufacturing (AM), also known as three-dimensional (3D) printing, to address thermal and electrical requirements in packaging gallium nitride (GaN) based high-electron-mobility transistors (HEMTs). The goal is to exploit design freedom and manufacturing flexibility provided by ceramic AM to fabricate power device packages with a lower junction-to-ambient thermal resistance (RθJA). Ceramic AM also enables incorporation of intricate 3D features into the package structure in order to control the isolation distance between the package source and drain contact pads. Moreover, AM allows to fabricate different parts of the packaging assembly as a single structure to avoid high thermal resistance interfaces. For example, the ceramic package and the ceramic heatsink can be printed as a single part without any bonding layer. Thermal simulations under different thermal loading and cooling conditions show the improvement of thermal performance of the package fabricated by ceramic AM. If assisted by an efficient cooling strategy, the proposed package has the potential to reduce RθJA by up to 48%. The results of the preliminary efforts to fabricate the ceramic package by AM are presented, and the challenges that have to be overcome for further development of this manufacturing method are recognized and discussed.
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| 4. |
- Alleaume, Pierre Franck, et al.
(författare)
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A highly integrated heterogeneous micro- and mm-wave platform
- 2010
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Ingår i: IEEE MTT-S International Microwave Symposium Digest. - 0149-645X. - 9781424477326 ; , s. 461-464
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A highly integrated platform for micro- and mmwave frequency applications is introduced. The platform utilizes heterogeneous process modules with integrated passive and tunable devices together with silicon and GaAs MMIC technology to achieve outstanding flexibility. The different process modules are accounted for and their feasibility is proven through a number of application demonstrators from 23GHz telecom backhauling and 77GHz automotive radar indicating excellent performance. © 2010 IEEE.
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| 5. |
- Baccarini, Andrea, et al.
(författare)
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Frequent new particle formation over the high Arctic pack ice by enhanced iodine emissions
- 2020
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- In the central Arctic Ocean the formation of clouds and their properties are sensitive to the availability of cloud condensation nuclei (CCN). The vapors responsible for new particle formation (NPF), potentially leading to CCN, have remained unidentified since the first aerosol measurements in 1991. Here, we report that all the observed NPF events from the Arctic Ocean 2018 expedition are driven by iodic acid with little contribution from sulfuric acid. Iodic acid largely explains the growth of ultrafine particles (UFP) in most events. The iodic acid concentration increases significantly from summer towards autumn, possibly linked to the ocean freeze-up and a seasonal rise in ozone. This leads to a one order of magnitude higher UFP concentration in autumn. Measurements of cloud residuals suggest that particles smaller than 30nm in diameter can activate as CCN. Therefore, iodine NPF has the potential to influence cloud properties over the Arctic Ocean. Which vapors are responsible for new particle formation in the Arctic is largely unknown. Here, the authors show that the formation of new particles at the central Arctic Ocean is mainly driven by iodic acid and that particles smaller than 30nm in diameter can activate as cloud condensation nuclei.
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| 6. |
- Cunliffe, Michael, et al.
(författare)
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Sea surface microlayers : A unified physicochemical and biological perspective of the air-ocean interface
- 2013
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Ingår i: Progress in Oceanography. - : Elsevier BV. - 0079-6611 .- 1873-4472. ; 109, s. 104-116
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Forskningsöversikt (refereegranskat)abstract
- The sea surface microlayer (SML) covers more than 70% of the Earth's surface and is the boundary layer interface between the ocean and the atmosphere. This important biogeochemical and ecological system is critical to a diverse range of Earth system processes, including the synthesis, transformation and cycling of organic material, and the air-sea exchange of gases, particles and aerosols. In this review we discuss the SML paradigm, taking into account physicochemical and biological characteristics that define SML structure and function. These include enrichments in biogenic molecules such as carbohydrates, lipids and proteinaceous material that contribute to organic carbon cycling, distinct microbial assemblages that participate in air-sea gas exchange, the generation of climate-active aerosols and the accumulation of anthropogenic pollutants with potentially serious implications for the health of the ocean. Characteristically large physical, chemical and biological gradients thus separate the SML from the underlying water and the available evidence implies that the SML retains its integrity over wide ranging environmental conditions. In support of this we present previously unpublished time series data on bacterioneuston composition and SML surfactant activity immediately following physical SML disruption; these imply timescales of the order of minutes for the reestablishment of the SML following disruption. A progressive approach to understanding the SML and hence its role in global biogeochemistry can only be achieved by considering as an integrated whole, all the key components of this complex environment.
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| 7. |
- D'Humières, Benoit, et al.
(författare)
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The C3PO project : A laser communication system concept for small satellites
- 2017
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 9781510606333
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Konferensbidrag (refereegranskat)abstract
- The satellite market is shifting towards smaller (micro and nanosatellites), lowered mass and increased performance platforms. Nanosatellites and picosatellites have been used for a number of new, innovative and unique payloads and missions. This trend requires new concepts for a reduced size, a better performance/weight ratio and a reduction of onboard power consumption. In this context, disruptive technologies, such as laser-optical communication systems, are opening new possibilities. This paper presents the C3PO1 system, "advanced Concept for laser uplink/ downlink CommuniCation with sPace Objects", and the first results of the development of its key technologies. This project targets the design of a communications system that uses a ground-based laser to illuminate a satellite, and a Modulating Retro-Reflector (MRR) to return a beam of light modulated by data to the ground. This enables a downlink, without a laser source on the satellite. This architecture suits well to small satellite applications so as high data rates are potentially provided with very low board mass. C3PO project aims to achieve data rates of 1Gbit/s between LEO satellites and Earth with a communication payload mass of less than 1kilogram. In this paper, results of the initial experiments and demonstration of the key technologies will be shown.
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| 8. |
- Ickes, Luisa, 1986, et al.
(författare)
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The ice-nucleating activity of Arctic sea surface microlayer samples and marine algal cultures
- 2020
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Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 20:18, s. 11089-11117
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Tidskriftsartikel (refereegranskat)abstract
- In recent years, sea spray as well as the biological material it contains has received increased attention as a source of ice-nucleating particles (INPs). Such INPs may play a role in remote marine regions, where other sources of INPs are scarce or absent. In the Arctic, these INPs can influence water-ice partitioning in low-level clouds and thereby the cloud lifetime, with consequences for the surface energy budget, sea ice formation and melt, and climate. Marine aerosol is of a diverse nature, so identifying sources of INPs is challenging. One fraction of marine bioaerosol (phytoplankton and their exudates) has been a particular focus of marine INP research. In our study we attempt to address three main questions. Firstly, we compare the ice-nucleating ability of two common phytoplankton species with Arctic seawater microlayer samples using the same instrumentation to see if these phytoplankton species produce ice-nucleating material with sufficient activity to account for the ice nucleation observed in Arctic microlayer samples. We present the first measurements of the ice-nucleating ability of two predominant phytoplankton species: Melosira arctica, a common Arctic diatom species, and Skeletonema marinoi, a ubiquitous diatom species across oceans worldwide. To determine the potential effect of nutrient conditions and characteristics of the algal culture, such as the amount of organic carbon associated with algal cells, on the ice nucleation activity, Skeletonema marinoi was grown under different nutrient regimes. From comparison of the ice nucleation data of the algal cultures to those obtained from a range of sea surface microlayer (SML) samples obtained during three different field expeditions to the Arctic (ACCACIA, NETCARE, and ASCOS), we found that they were not as ice active as the investigated microlayer samples, although these diatoms do produce ice-nucleating material. Secondly, to improve our understanding of local Arctic marine sources as atmospheric INPs we applied two aerosolization techniques to analyse the ice-nucleating ability of aerosolized microlayer and algal samples. The aerosols were generated either by direct nebulization of the undiluted bulk solutions or by the addition of the samples to a sea spray simulation chamber filled with artificial seawater. The latter method generates aerosol particles using a plunging jet to mimic the process of oceanic wave breaking. We observed that the aerosols produced using this approach can be ice active, indicating that the ice-nucleating material in seawater can indeed transfer to the aerosol phase. Thirdly, we attempted to measure ice nucleation activity across the entire temperature range relevant for mixed-phase clouds using a suite of ice nucleation measurement techniques - an expansion cloud chamber, a continuous-flow diffusion chamber, and a cold stage. In order to compare the measurements made using the different instruments, we have normalized the data in relation to the mass of salt present in the nascent sea spray aerosol. At temperatures above 248K some of the SML samples were very effective at nucleating ice, but there was substantial variability between the different samples. In contrast, there was much less variability between samples below 248 K. We discuss our results in the context of aerosol-cloud interactions in the Arctic with a focus on furthering our understanding of which INP types may be important in the Arctic atmosphere.
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| 9. |
- Jergil, Måns, et al.
(författare)
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Exploring Transcriptional Response toValproic Acid and Valproic Acid Analogs in Human Embryonic Stem Cells
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Annan publikation (populärvet., debatt m.m.)abstract
- Developmental toxicity is a major concern for manufacturers of new pharmaceuticals,and current testing requires many laboratory animals. Human embryonic stem (hES)cells, potentially being close in function to cells in the developing embryo, mayprovide a technology for classification of candidate drugs in the early phase of toxicityevaluation. Altered gene expression in such system may be predictive of teratogenicproperties of a substance if important gene regulatory pathways are affected, and mayhence be used as appropriate endpoint. In the present study we used the pluripotenthES cell line SA002 (Cellartis AB), and microarrays to profile the response tovalproic acid (VPA), a known human teratogen causing increased risk of e.g. spinabifida and cognitive disorders in exposed embryos We also investigated three closelyrelated VPA analogs with differing in vivo teratogenicity in mice as well as histonedeacetylase (HDAC) inhibition, a proposed teratogenic mechanism of VPA. hEScells in an undifferentiated state were exposed for 24 h to either 1 mM VPA, 0.25mM or 0.5 mM (S)-2-pentyl-4-pentynoic acid a more potent teratogen and HDACinhibitor than VPA, 1 mM 3-propyl-heptanoic acid, a potent teratogen but not anHDAC inhibitor, 1 mM 2-ethyl-4-methyl-pentanoic acid, a non-teratogen and non-HDAC inhibitor, or 0.1% DMSO. Gene expression was subsequently profiled usingCodelink Human Whole Genome BioArrays. We found the HDAC inhibitors tostrongly deregulate largely the same genes. Further, a concordance of altered geneontology groups, predominantly neurogenic processes, was evident between all theteratogenic substances. Also, comparison with mouse ES cells showed an overlap ofderegulated genes as well as species specific gene to be deregulated.
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| 10. |
- Jergil, Måns, 1975-, et al.
(författare)
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Short-Time Gene Expression Response to Valproic Acid and Valproic Acid analogs in Mouse Embryonic Stem Cells
- 2011
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Ingår i: Toxicological Sciences. - : Oxford University Press (OUP). - 1096-6080 .- 1096-0929. ; 121:2, s. 328-342
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Tidskriftsartikel (refereegranskat)abstract
- The prediction of potential developmental toxicity in vitro could be based ontoxicogenomic endpoints a short time after exposure in cultured embryo-derived celllines. Our previous microarray studies in P19 mouse embryonal carcinoma cells andmouse embryos have indicated that the teratogen valproic acid (VPA), an inducerof neural tube defects, deregulates the expression of a large number of genes, manyof which have critical roles in neural tube formation and closure. In this study weexposed undifferentiated R1 mouse embryonic stem (ES) cells to VPA and VPA analogto define genes whose expression responses may be related to teratogenic potential.After 6 h of exposure, RNA samples were subjected to microarray analysis usingCodeLinkTM Mouse Whole Genome Bioarrays. VPA (1 mM) and the teratogenic VPAanalog (S)-2-pentyl-4-pentynoic (0.25 mM or 0.5 mM) deregulate a large numberof genes, whereas for the non-teratogenic (and potentially pharmacologically active)analog 2-ethyl-4-methyl-pentanoic acid (1 mM) the expression of only a few geneswas affected. Biological process ontology groups related to embryonic development,morphogenesis, and cell behavior were overrepresented among the affected teratogentarget genes. Multivariate analysis indicated that as few as five genes (out of ~2500array probes correlating with the separation) could separate the data set accordingto teratogenicity. Genes deregulated by the two teratogens showed a substantialoverlap with genes previously found to be deregulated by VPA in P19 cells and mouseembryos. A panel of candidate genes was defined as potential markers predictiveof teratogenicity and evaluated through TaqMan low density array analysis. Theteratogens butyrate and trichostatin A, which like VPA and (S)-2-pentyl-4-pentynoicacid are known histone deacetylase (HDAC) inhibitors, induced similar responsesas these two teratogens for a large subset of markers. This indicates that HDACinhibition may be a major mechanism by which VPA induces gene deregulation andpossibly teratogenicity. Other teratogenic compounds tested had no effect on thepanel of selected markers, indicating that they may not be predicitive of teratogenicityfor compounds acting through other mechanisms than VPA.
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