| 1. |
- Imani Jajarmi, Ramin, 1987-
(författare)
-
Acoustic separation of submicron particles in gaseous flows
- 2015
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The separation of submicron particles suspended in gaseous flows is a problem of great importance and is the subject of sustained research efforts. This is motivated by several challenges presented by modern science and technology requiring high separation efficiencies for submicron particles.Continuous acoustic particles separation is a novel technique based on the acoustophoresis phenomenon, in which a particle within an acoustic field is manipulated using acoustic forces on its surface. This technique has the potential to overcome some of the limitations of common techniques for the separation of submicron particles, as well as performing advanced tasks such as sorting particles according to their size or density.In this thesis, the separation of submicron solid particles suspended in air is investigated experimentally, with a focus on the effect of key design parameters (acoustic, flow, geometry) on the efficiency of the process. A simple method based on laser light scattering was also used to provide qualitative information on the particle number density as a function of position in the channel. This technique allowed to quickly investigate the effect of a wide range of parameters on the acoustic separation efficiency including the pressure amplitude, the frequency of the standing wave, the average flow velocity and the parallelism of the channel walls. The results demonstrate conclusively that acoustic manipulation is possible for submicron particles and that the acoustic force scales following the trends expected from theoretical models developed in the continuum regime. From the size of the particles used it however follows that the observed separation is the result of transition regime acoustophoresis, with a Knudsen number on the order of 0.2.
|
|
| 2. |
- Barrdunge, Mats, 1956-
(författare)
-
Upplysningens ljus i Norrland : Om fyra aktörer vid Härnösands gymnasium under 1700-talet
- 2024
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The purpose of this dissertation is to investigate the occurrence of Enlightenment ideas in the central Northern part of Sweden during the 18th century, focussing on a carefully chosen set of characters: one bishop and three senior lecturers at the gymnasium of Härnösand, in the province of Ångermanland. This dissertation uses a perspective of circulation of knowledge, inspired by the research field of history of knowledge. The methodological approach in this study is to use a complex thematic definition with eight different components of Enlightenment in the analysis of relevant texts and writings by selected characters, supplemented with a contextual perspective.A center for the ecclesiastical culture of learning in Norrland was Härnösand, and the gymnasium was Norrland´s only higher education institution, north of Gävle, for 200 years between 1650 and 1850. During the 18th century, three senior lecturers were employed there, each working for the dissemination of Enlightenment ideas, through both writing and practical action: Magnus Stridsberg (1696–1772), Nils Gissler (1715–1771) and Pehr Hellzén (1744–1811). At the same time as these, the diocese was governed by Bishop Olof Kiörning (1704–1778), who was also the Supervisor of the gymnasium. He was influenced by Enlightenment ideas and showed a strong interest in advanced agriculture and contributed to the church taking greater part in the social and economic development. The first lecturer, Magnus Stridsberg, created new methods in agriculture concerning soil mixing, manure production and grain nurseries, but has mainly been remembered for his threshing machine which came into general use in central Norrland during the second half of the 18th century. The next lecturer, Nils Gissler, was Norrland´s first provincial physician and introduced a scientific approach to practical medicine in the region. With the dissemination of knowledge and a great deal of personal commitment, he showed interest in mental illness and treated his patients in his own home. He laid the foundation for an infrastructure for public health care in the province. He was a member of the Swedish Academy of Sciences and wrote many scientific papers, and in modern times has received international scientific recognition for the discovery of the inverted barometer effect. The third lecturer, Pehr Hellzén, was a pre-industrial contractor in the sawmill and shipbuilding industry in central Norrland and founded the shipyard and shipping company Wifstavarf in 1798. Hellzén gave an important inaugural speech when the new gymnasium was built: Om uplysningens verkan på människors och samhällens sällhet (On the effect of Enlightenment on the happiness of people and societies), printed in Swedish 1794. He gave Härnösand a special role within the Enlightenment, described as a driving force behind the development of science, education and economic in the region.The Enlightenment that developed in Härnösand can be summarized as a Christian ‘utilism’ with clear Enlightenment traits such as reason, experience-based science, the dissemination of knowledge, humanity, social reforms, religious tolerance & religion of reason, and utility & virtue. It rested on an evangelical Lutheran foundation, it regarded the meaning of ‘utilism’ in a broader sense than just financial gain, and included central Enlightenment ideas.
|
|
| 3. |
- Bergman, Martin, 1981-
(författare)
-
The evolution of territoriality in butterflies
- 2011
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Competition over mating opportunities is a conspicuous characteristic of animal behaviour. In many butterfly species the males establish territories in places advantageous for encountering females. This thesis addresses questions about how territoriality has evolved and is maintained in butterflies. The studies have been conducted using the speckled wood butterfly, Pararge aegeria, as a model species. Males of P. aegeria are found in sunspots on the forest floor (paper I-V), on the lookout for females visiting the sunspots. However, males are only found in sunspots above a certain size (paper III). This behavior is maintained by a mating success advantage, where using large sunspots instead of small sunspots as perching areas generates a higher reproductive output (paper I). The mating success asymmetry is not explained by female choice or by a female preference for large sunspots per se (paper I, V), but rather the large sunspot facilitates visual performance of perching males and improves flight pursuit and interception of females (paper III). Winners of territorial contests gain sole ownership of large sunspot territories, while losers search for a new suitable sunspot territory (paper I, II & IV) or use smaller, suboptimal sunspots as perching sites (paper II). Territorial contests between P. aegeria males are not settled due to an obvious morphological/physiological asymmetry (paper I). Rather, variation in resource value and motivational asymmetries are important for settling contests (paper IV). A majority of male-female interactions (paper V) and matings (paper I) are initiated by a perching male detecting and intercepting a flying female. Furthermore, females can affect their chances of being detected by a perching male by behaving more conspicuously (paper V). This thesis highlights the role of female behaviour, variation in resource value and motivation asymmetries to understand the evolution of territoriality in butterflies.
|
|
| 4. |
- Christakou, Athanasia, 1977-
(författare)
-
Ultrasound-assisted Interactions of Natural Killer Cells with Cancer Cells and Solid Tumors
- 2014
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this Thesis, we have developed a microtechnology-based method for culturing and visualizing high numbers of individual cells and cell-cell interactions over extended periods of time. The foundation of the device is a silicon-glass multiwell microplate (also referred as microchip) directly compatible with fluorescence microscopy. The initial microchip design involved thousands of square wells of sizes up to 80 µm, for screening large numbers of cell-cell interactions at the single cell level. Biocompatibility and confinement tests proved the feasibility of the idea, and further investigation showed the conservation of immune cellular processes within the wells. Although the system is very reliable for screening, limitations related to synchronization of the interaction events, and the inability to maintain conjugations for long time periods, led to the development of a novel ultrasonic manipulation multiwell microdevice.The main components of the ultrasonic device is a 100-well silicon-glass microchip and an ultrasonic transducer. The transducer is used for ultrasonic actuation on the chip with a frequency causing half-wave resonances in each of the wells (2.0-2.5 MHz for wells with sizes 300-350 µm). Therefore, cells in suspension are directed by acoustic radiation forces towards a pressure node formed in the center of each well. This method allows simultaneous aggregation of cells in all wells and sustains cells confined within a small area for long time periods (even up to several days).The biological target of investigation in this Thesis is the natural killer (NK) cells and their functional properties. NK cells belong to the lymphatic group and they are important factors for host defense and immune regulation. They are characterized by the ability to interact with virus infected cells and cancer cells upon contact, and under suitable conditions they can induce target cell death. We have utilized the ultrasonic microdevice to induce NK-target cell interactions at the single cell level. Our results confirm a heterogeneity within IL-2 activated NK cell populations, with some cells being inactive, while others are capable to kill quickly and in a consecutive manner.Furthermore, we have integrated the ultrasonic microdevice in a temperature regulation system that allows to actuate with high-voltage ultrasound, but still sustain the cell physiological temperature. Using this system we have been able to induce formation of up to 100 solid tumors (HepG2 cells) in parallel without using surface modification or hydrogels. Finally, we used the tumors as targets for investigating NK cells ability to infiltrate and kill solid tumors. To summarize, a method is presented for investigating individual NK cell behavior against target cells and solid tumors. Although we have utilized our technique to investigate NK cells, there is no limitation of the target of investigation. In the future, the device could be used for any type of cells where interactions at the single cell level can reveal critical information, but also to form solid tumors of primary cancer cells for toxicology studies.
|
|
| 5. |
- Olofsson, Martin, 1980-
(författare)
-
Antipredator defence in butterflies
- 2013
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Predation exerts a potent selection mechanism and has resulted in a suite of antipredation adaptations encompassing morphological and behavioral traits in prey. In butterflies, several such traits appear to be directed towards birds which are considered as one of their major predators. In this thesis I have investigated tactics by which adult butterflies may survive close encounters with birds. In paper I, I provide supporting evidence that the small white “comma” on females of the comma butterfly, Polygonia c-album, has a distractive function on blue tits and so reduces the attack risk. In paper II & III, I investigate the antipredator efficiency of sudden wing-flicking in two species, the peacock butterfly, Inachis io, and the European swallowtail, Papilio machaon, when confronted with domestic fowl and great tits, respectively. Peacock butterflies were manipulated to either display visible or painted over eyespots. Interestingly, the birds that confronted peacocks with visible eyespots were more likely to utter antipredator alarm calls, which imply that the eyespots may be perceived as real eyes of a potential predator. On the whole, wing-flicking in both species typically induced evasion in the birds which suggests that the birds became frightened rather than perceiving the butterflies as not profitable to attack for some other reason. Moreover, I use blue tits as predators to investigate the possible function of smaller eyespots of satyrine butterflies in that they serve to divert predator attacks. Evidence suggests that low light conditions accentuated in the UV may enhance the deflective function of marginal eyespots in the woodland brown butterfly, Lopinga achine (paper IV). In paper V, I show that the presence of one marginal eyespot on the speckled wood butterfly, Pararge aegeria, can deflect bird attacks; moreover, when the butterfly is concealed against the background, eyespots can also increase the latency time until bird attack. In conclusion, my thesis underscores that behavioral studies of predators are instrumental to aid our understanding of the adaptive significance of certain behavioral and morphological traits in prey.
|
|
| 6. |
|
|
| 7. |
- Svennebring, Jessica, 1979-
(författare)
-
Ultrasonic Handling of Living Cells in Microfluidic Systems
- 2009
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Microfluidic chips have become a powerful tool in research where biological cells are processed and/or analyzed. One method for contactless cell manipulation in microfluidic chips that has gained an increasing amount of attention the last decade is ultrasonic standing wave (USW) technology. This Thesis explores the biocompatibility of USW technology applied to microfluidic chips, and presents a novel USW-based method for serial processing and accurate characterization of living cells. The biocompatibility has been investigated by measuring the proliferation rate of cells after they had been trapped and aggregated inside a chip by ultrasound. No negative influence was observed after continuous exposure to 0.85 MPa pressure amplitudes for up to 75 min. Furthermore, the heat generation in the fluid channel caused by the ultrasound has been measured and used in a regulation scheme where the temperature can be controlled around any relevant temperature (e.g. 37‰) with ±0.1‰ accuracy for more than 12 hours. The proliferation rate and temperature investigations suggest that USW technology applied to microfluidic chips is a biocompatiblemethod useful for long-term handling of living cells. We have introduced a new concept of contactless ultrasonic ”caging” of single cells or small aggregates of cells. These cages are channel segments in the microfluidic chips that are geometrically designed to resonate at one or several actuation frequencies. The actuation is performed remotely by up to five external frequency specific wedge transducers, where each transducer produces a localized and spatially confined standing wave with a specific orientation of its corresponding radiation force field. By multi-frequency actuation, sophisticated and flexible force fields are realized by both overlapping and separated single fields. The Thesis describes two different cages: A sub-mm ”micro-cage” for tree-dimensional manipulationof single cells, and a 5-mm ”mini-cage” for selective retention of small cell aggregates (up to approx. 10^3 cells) from a continuously feeding sample flow. Finally,our microfluidic chips were also designed to be compatible with high-resolution optical microscopy. We have demonstrated sub-μm-resolution confocal fluorescence and trans-illumination microscopy imaging of ultrasonically caged living cells.
|
|
| 8. |
- Ghorbani, Morteza, et al.
(författare)
-
Unravelling the Acoustic and Thermal Responses of Perfluorocarbon Liquid Droplets Stabilized with Cellulose Nanofibers
- 2019
-
Ingår i: Langmuir. - : American Chemical Society. - 0743-7463 .- 1520-5827. ; 35:40, s. 13090-13099
-
Tidskriftsartikel (refereegranskat)abstract
- The attractive colloidal and physicochemical properties of cellulose nanofibers (CNFs) at interfaces have recently been exploited in the facile production of a number of environmentally benign materials, e.g. foams, emulsions, and capsules. Herein, these unique properties are exploited in a new type of CNF-stabilized perfluoropentane droplets produced via a straightforward and simple mixing protocol. Droplets with a comparatively narrow size distribution (ca. 1-5 μm in diameter) were fabricated, and their potential in the acoustic droplet vaporization process was evaluated. For this, the particle-stabilized droplets were assessed in three independent experimental examinations, namely temperature, acoustic, and ultrasonic standing wave tests. During the acoustic droplet vaporization (ADV) process, droplets were converted to gas-filled microbubbles, offering enhanced visualization by ultrasound. The acoustic pressure threshold of about 0.62 MPa was identified for the cellulose-stabilized droplets. A phase transition temperature of about 22 °C was observed, at which a significant fraction of larger droplets (above ca. 3 μm in diameter) were converted into bubbles, whereas a large part of the population of smaller droplets were stable up to higher temperatures (temperatures up to 45 °C tested). Moreover, under ultrasound standing wave conditions, droplets were relocated to antinodes demonstrating the behavior associated with the negative contrast particles. The combined results make the CNF-stabilized droplets interesting in cell-droplet interaction experiments and ultrasound imaging.
|
|
| 9. |
- Imani Jajarmi, Ramin
(författare)
-
Acoustic separation and electrostatic sampling of submicron particles suspended in air
- 2016
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- We investigate experimentally the effects of acoustic forces on submicron aerosol in a channel flow. This technique can potentially overcome some of the limitations of conventional separation systems and provide advanced manipulation capabilities such as sorting according to size or density. The theoretical framework for acoustophoresis at such small length scales where molecular effects are expected to be significant is still incomplete and in need of experimental validation. The main objectives of this thesis are to identify the physical limitations and capabilities of acoustophoretic manipulation for submicron aerosol particles.Two sets of experiments were carried out: first, qualitative results revealed that acoustic manipulation is possible for submicron particles in air and that the acoustic force follows the trend expected by theoretical models developed for particles in inviscid fluids. The acoustic force on submicron particles was estimated in a second set of measurements performed with quantitative diagnostic tools. Comparison of these results with available theoretical models for the acoustic radiation forces demonstrates that for such small particles additional forces have to be considered. At submicron length scales, the magnitude of the forces observed is orders of magnitude higher than the predictions from the inviscid theory.One potential application for acoustophoresis is specifically investigated in this thesis: assist electrostatic precipitation (ESP) samplers to target very small aerosols, such as those carrying airborne viruses. To identify the shortcomings of ESP samplers that acoustophoresis should overcome, two ESP designs have been investigated to quantify capture efficiency as a function of the particle size and of the air velocity in a wind tunnel. The results reveal that both designs have limitations when it comes to sampling submicron aerosol particles. When exposed to polydispersed suspensions they behave as low-pass filters.
|
|
| 10. |
- Loskutova, Ksenia, et al.
(författare)
-
Assessment of the Mechanical Propertiesof Cellulose Nanofiber-Stabilized Droplets Using Acoustophoresis
- 2021
-
Konferensbidrag (refereegranskat)abstract
- In this work, the compressibility of Pickering-stabilized perfluoropentane droplets was determined by using acoustophoresis. Polyamide beads with known density, size and compressibility were used to calculate the pressure amplitude inside the microchannel. The results show that the compressibility of CNF-stabilized droplets is significantly higher than for water, but lower than for pure PFC5. This shows promising potential for these droplets to be used in ultrasound-mediated clinical applications. It has also been shown that acoustophoresis can successfully measure the compressibility of pressure-sensitive particles for small USW pressure amplitudes. As the droplets relocate to pressure anti-nodes just as gas-filled microbubbles, it would be possible to study cell-droplet and cell-gasbubble in the same setup.
|
|
