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  • 1.
    Albernaz, Daniel L.
    et al.
    KTH.
    Do-Quang, Minh
    KTH.
    Hermanson, James C.
    University of Washington, Seattle, USA.
    Amberg, Gustav
    KTH.
    Thermodynamics of a real fluid near the critical point in numerical simulations of isotropic turbulence2016Inngår i: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 28, nr 12, artikkel-id 125105Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We investigate the behavior of a fluid near the critical point by using numerical simulations of weakly compressible three-dimensional isotropic turbulence. Much has been done for a turbulent flow with an ideal gas. The primary focus of this work is to analyze fluctuations of thermodynamic variables (pressure, density, and temperature) when a non-ideal Equation Of State (EOS) is considered. In order to do so, a hybrid lattice Boltzmann scheme is applied to solve the momentum and energy equations. Previously unreported phenomena are revealed as the temperature approaches the critical point. Fluctuations in pressure, density, and temperature increase, followed by changes in their respective probability density functions. Due to the non-linearity of the EOS, it is seen that variances of density and temperature and their respective covariance are equally important close to the critical point. Unlike the ideal EOS case, significant differences in the thermodynamic properties are also observed when the Reynolds number is increased. We also address issues related to the spectral behavior and scaling of density, pressure, temperature, and kinetic energy.

  • 2.
    Bredenberg, Johan
    et al.
    Södertörns högskola, Avdelning Naturvetenskap.
    Nilsson, L
    Modeling zinc sulfhydryl bonds in zinc fingers2001Inngår i: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 83, nr 3-4, s. 230-244Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Molecular dynamics simulations have been carried out employing three different model descriptions of the zinc sulfhydryl interactions in class II fingers. One bonded and two nonbonded models were studied. Two variant structures of the glucocorticoid receptor DNA-binding; domain and a NMR structure from a fragment of methionyl-tRNA synthetase were subjected to long-time MD simulations with these models. Our analysis is focused on comparison with experimental and quantum mechanical data, concerning the local Zn-finger and overall structural and dynamic properties for these models. All models performed M ell, but the nonbonded models appeared to reproduce the protein dynamics in better agreement with experimental data than does the bonded description.

  • 3.
    Carlson, Andreas
    et al.
    KTH.
    Do-Quang, Minh
    KTH.
    Amberg, Gustav
    KTH.
    Dissipation in rapid dynamic wetting2011Inngår i: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 682, s. 213-240Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this article, we present a modelling approach for rapid dynamic wetting based on the phase field theory. We show that in order to model this accurately, it is important to allow for a non-equilibrium wetting boundary condition. Using a condition of this type, we obtain a direct match with experimental results reported in the literature for rapid spreading of liquid droplets on dry surfaces. By extracting the dissipation of energy and the rate of change of kinetic energy in the flow simulation, we identify a new wetting regime during the rapid phase of spreading. This is characterized by the main dissipation to be due to a re-organization of molecules at the contact line, in a diffusive or active process. This regime serves as an addition to the other wetting regimes that have previously been reported in the literature.

  • 4.
    Carlson, Andreas
    et al.
    KTH / Harvard University, Cambridge, United States / Princeton University, Princeton, United States.
    Kim, P.
    Korea Advanced Institute of Science and Technology, Daejeon, South Korea / Princeton University, Princeton, United States.
    Amberg, Gustav
    KTH.
    Stone, H. A.
    Princeton University, Princeton, United States.
    Short and long time drop dynamics on lubricated substrates2013Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 104, nr 3, artikkel-id 34008Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Liquid infiltrated solids have been proposed as functional solvent-phobic surfaces for handling single and multiphase flows. Implementation of such surfaces alters the interfacial transport phenomenon as compared to a dry substrate. To better understand the interface characteristics in such systems we study experimentally the dynamics of a pendant water drop in air that contacts a substrate coated by thin oil films. At short times the water drop is deformed by the oil that spreads onto the water-air interface, and the dynamics are characterized by inertial and viscous regimes. At late times, the the oil film under the drop relaxes either to a stable thin film or ruptures. In the thin film rupture regime, we measure the waiting time for the rupture as a function of the drop equilibrium contact angle on a dry substrate and the initial film height. The waiting time is rationalized by lubrication theory, which indicates that long-range intermolecular forces destabilize the oil-water interface and is the primary mechanism for the film drainage.

  • 5.
    Do-Quang, Minh
    et al.
    KTH.
    Shiomi, Junichiro
    University of Tokyo, Tokyo, Japan / CREST, Japan Science and Technology Agency, Tokyo, Japan.
    Amberg, Gustav
    KTH.
    When and how surface structure determines the dynamics of partial wetting2015Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 110, nr 4, artikkel-id 46002Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The motion of a three phase contact line, as in a droplet spreading over a dry surface, is ubiquitous in nature and common in technology, but is still not well understood. As has been recently shown, line friction may play an important role in rapid dynamic wetting. Recognizing this as a sometimes dominating factor, we identify the possible scenarios for dynamic wetting of a partially wetting fluid, given the fluid and substrate properties. In doing so, we also reconcile the seemingly different interpretations of dynamic wetting that have been put forward in the recent literature. Copyright (C) EPLA, 2015

  • 6.
    Kekesi, Timea
    et al.
    KTH.
    Amberg, Gustav
    KTH.
    Wittberg, L. Prahl
    KTH.
    Drop deformation and breakup in flows with shear2016Inngår i: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 140, s. 319-329Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A Volume of Fluid (VOF) method is applied to study the deformation and breakup of a single liquid drop in shear flows superimposed on uniform flow. The effect of shearing on the breakup mechanism is investigated as a function of the shear rate. Sequential images are compared for the parameter range studied; density ratios of liquid to gas of 20, 40, and 80, viscosity ratios in the range 0.5-50, Reynolds numbers between 20, a constant Weber number of 20, and the non-dimensional shear rate of the flow G = 0-2.1875. It is found that while shear breakup remains similar for all values of shear rate considered, other breakup modes observed for uniform flows are remarkably modified with increasing shear rate. The time required for breakup is significantly decreased in strong shear flows. A simple model predicting the breakup time as a function of the shear rate and the breakup time observed in uniform flows is suggested.

  • 7.
    Knaust, Stefan
    et al.
    Uppsala University.
    Andersson, Martin
    Uppsala University.
    Rogeman, Niklas
    Uppsala University.
    Hjort, Klas
    Uppsala University.
    Amberg, Gustav
    KTH.
    Klintberg, Lena
    Uppsala University.
    Influence of flow rate, temperature and pressure on multiphase flows of supercritical carbon dioxide and water using multivariate partial least square regression2015Inngår i: Journal of Micromechanics and Microengineering, ISSN 0960-1317, E-ISSN 1361-6439, Vol. 25, nr 10, artikkel-id 105001Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Supercritical carbon dioxide (scCO(2)) is often used to replace harmful solvents and can dissolve a wide range of organic compounds. With a favorable critical point at 31 degrees C and 7.4 MPa, reaching above the critical point for scCO(2) is fairly accessible. Because of the compressible nature of scCO(2) and the large changes of viscosity and density with temperature and pressure, there is a need to determine the behavior of scCO(2) in microfluidic systems. Here, the influence of how parameters such as flow rate, temperature, pressure, and flow ratio affects the length of parallel flow of water and scCO(2) and the length of the created CO2 segments are investigated and modeled using multivariate data analysis for a 10 mm long double-y channel. The parallel length and segment size were observed in the laminar regime around and above the critical point of CO2. The flow ratio between the two fluids together with the flow rate influenced both the parallel length and the segment sizes, and a higher pressure resulted in shorter parallel lengths. Regarding the segment length of CO2, longer segments were a result of a higher Weber number for H2O together with a higher temperature in the channel.

  • 8. Lebedeva, Natalia F.
    Одномерные нестационарные задачи об ударном нагружении несжимаемых упругих сред[One-dimensional non-stationary problems of shock loading uncompressible elastic solids]1997Doktoravhandling, monografi (Annet vitenskapelig)
  • 9.
    Liu, Jiewei
    et al.
    KTH.
    Amberg, Gustav
    KTH.
    Do-Quang, Minh
    KTH.
    Diffuse interface method for a compressible binary fluid2016Inngår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 93, nr 1, artikkel-id 013121Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Multicomponent, multiphase, compressible flows are very important in real life, as well as in scientific research, while their modeling is in an early stage. In this paper, we propose a diffuse interface model for compressible binary mixtures, based on the balance of mass, momentum, energy, and the second law of thermodynamics. We show both analytically and numerically that this model is able to describe the phase equilibrium for a real binary mixture (CO2 + ethanol is considered in this paper) very well by adjusting the parameter which measures the attraction force between molecules of the two components in the model. We also show that the calculated surface tension of the CO2 + ethanol mixture at different concentrations match measurements in the literature when the mixing capillary coefficient is taken to be the geometric mean of the capillary coefficient of each component. Three different cases of two droplets in a shear flow, with the same or different concentration, are simulated, showing that the higher concentration of CO2 the smaller the surface tension and the easier the drop deforms.

  • 10.
    Ogden, S.
    et al.
    Uppsala University.
    Boden, R.
    Uppsala University.
    Do-Quang, Minh
    KTH.
    Wu, Z. G.
    Uppsala University.
    Amberg, Gustav
    KTH.
    Hjort, K.
    Uppsala University.
    Fluid behavior of supercritical carbon dioxide with water in a double-Y-channel microfluidic chip2014Inngår i: Microfluidics and Nanofluidics, ISSN 1613-4982, E-ISSN 1613-4990, Vol. 17, nr 6, s. 1105-1112Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The use of supercritical carbon dioxide (scCO(2)) as an apolar solvent has been known for decades. It offers a greener approach than, e.g., hexane or chloroform, when such solvents are needed. The use of scCO(2) in microsystems, however, has only recently started to attract attention. In microfluidics, the flow characteristics need to be known to be able to successfully design such components and systems. As supercritical fluids exhibit the exciting combination of low viscosity, high density, and high diffusion rates, the fluidic behavior is not directly transferrable from aqueous systems. In this paper, three flow regimes in the scCO(2)-liquid water two-phase microfluidic system have been mapped. The effect of both total flow rate and relative flow rate on the flow regime is evaluated. Furthermore, the droplet dynamics at the bifurcating exit channel are analyzed at different flow rates. Due to the low viscosity of scCO(2), segmented flows were observed even at fairly high flow rates. Furthermore, the carbon dioxide droplet behavior exhibited a clear dependence on both flow rate and droplet length.

  • 11.
    Senatore Eriksson, Cecilia
    et al.
    Södertörns högskola, Institutionen för ekonomi och företagande.
    Elfner, Johanna
    Södertörns högskola, Institutionen för ekonomi och företagande.
    Fusion och Organisationskultur: En studie på Skruf Snus AB2007Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [en]

    Mergers between companies has become more and more common in Sweden and in the rest of the world with the motive to increase the competitive strength in the current markets and has an important role within organisational development of companies. When organisations merger there is not only buildings and objects that are put together but also their individual organisational structures, people, values and cultures. This can be a difficult process and can affect many people in how they think conscious as well as unconscious, feel and react.

    The purpose of this thesis is to gain a deeper understanding of how employees are affected following a merger when changes in the organisational culture come up, and how these changes are expressed.

    This thesis is delimited to investigate only one company, Skruf Snus AB and only focus on their business and employees in the region of Stockholm. The thesis contains a qualitative investigation with semi structured interviews that has been carried out with eight employees at Skruf Snus AB. The thesis is partly based on a model of Schein which describes the different levels in organisational culture and partly on some theories about reactions to change in relation to the integration between the employees following a merger.

    The results of the investigation indicate that with a merger the whole organisational culture is affected and therefore also the employees. Routines, communication, loyalty and relations have been changed. A gain of stress, anxiety, sadness and disappointment appears between the employees. This is often a result of lack of information and indistinct directives. Concepts like “Us and Them” are created, both unconscious and conscious and are permeated through the entire organisation.

    Fulltekst (pdf)
    FULLTEXT01
  • 12.
    Svensson, Melina
    Södertörns högskola, Lärarutbildningen.
    Förklaringar av ämnesspecifika begrepp i fysikens läroböcker: En läromedelsanalys för årskurs 4–62018Independent thesis Advanced level (professional degree), 10 poäng / 15 hpOppgave
    Abstract [en]

    The purpose with this thesis is to see which subject-specific concepts occur in middle school physics textbooks in the solar system. The second goal of the work is to analyze how these subject-specific concepts are explained to give an understanding of the concepts. This empirical work attempts to answer two questions:• What subject-specific concepts are found about the solar system in middle school physics textbooks?• How are the subject-specific concepts of the solar system explained so that they provide an understanding of the concepts?To answer these questions, a quantitative content analysis and a qualitative text analysis were made. The methods were applied to three different Swedish middle school textbooks. The theoretical framework used in this work is subject-specific concepts, analogies, metaphors and conceptual development. Subject-specific concepts are used to define the subject-specific concepts. Analogies and metaphors are used as a pair of glasses to show how students can acquire new concepts. The theory of conceptual development was used to gain perspective on how students understand new concepts. What I found out was that the subject-specific concepts used to explain our solar system were sun, moon, planet, earth, asteroid, earth axis, solar system, celestial bodies, gravity, attraction, dwarf planets, comets and crater. The result showed that none of the textbooks used analogies. A few metaphors were used but the explanations that appeared as the most except for no use were examples and relationships. In two textbooks some subject-specific concepts had been introduced earlier several times.Keywords: Physics, textbook, explained, solar system.Nyckelord: Fysik, lärobok, förklaringar, solsystemet.

    Fulltekst (pdf)
    fulltext
  • 13.
    Tamadoni, Anilin
    Södertörns högskola, Institutionen för ekonomi och företagande.
    AstraZeneca: Vikten av intern marknadsföring och kommunikation i samband med fusioner2007Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [en]

    In the society of today it’s very hard for companies to succeed with mergers. (A.L.Pablo, M.Javidan:2004) This study intends to elucidate the importance of internal marketing and internal communication with mergers. The intention with this essay is to study and analyse the merger between the two companies Astra and Zeneca and study the employers at the time when the merger took place in 1999.

    I have chosen to do this study on the basis of an employer’s perspective. I have used existing theories as internal communication, internal marketing and mergers and acquisition. The empirical data is based on a questionnaire focusing on how the employers handled the merger AstraZeneca. The questionnaire was responded by 60 employers from AstraZeneca.

    The conclusion in this study is that internal marketing and internal communication are really important for mergers to succeed and that the internal marketing and communication in AstraZeneca was well organised. That was the main reason for AstraZeneca’s success. Companies should understand the importance of internal cooperation especially with mergers, when a lot of knowledge and information is vital for succeed.

    Fulltekst (pdf)
    FULLTEXT01
  • 14.
    Urthaler, Stephanie
    Södertörns högskola, Lärarutbildningen.
    Tränas förmågorna i ämnet fysik?: En innehållsanalys av lärarnas planeringar, LPP:er samt hur lärarna övar förmågorna med eleverna i ämnet fysik.2017Independent thesis Advanced level (professional degree), 10 poäng / 15 hpOppgave
    Abstract [en]

    Abstract - Which abilities are the students training in the subject of physics?

    The purpose of this study was to examine teachers' plans, LPPs (Local Educational Planning) to see which abilities are trained and how. I have created a content analysis of the teachers' plans, LPPs and how the teachers practice the abilities of the students in the subject of physics. I analysed two LPPs in the grade 5 and two LPPs in the grade 6. The LPPs are from two different schools and two teachers' one in each grade. My first purpose was to examine which abilities, prescribed in Lgr 11 students are training and if the abilities create a common thread between grade 5 and grade 6 in the subject of physics. My second purpose was to examine what kind of teaching the students are training the abilities which can be found in Lgr 11. The study addresses three different kinds of teaching which are more open, more guided or in a combined way of teaching. My study answered the following questions:

    • Which abilities in Lgr 11 are the students training in the subject of physics in grade 5 and 6?
    • What kind of teaching are the students training the abilities in Lgr 11?

    The study was based on a content analysis of the LPPs and the theory I used to analyse was The Big 5. I also used interview by email with the teachers who gave me the LPPs. Based on the results and the analysis of the study, I came to the conclusion that all four LPPs in the two different schools were practicing the abilities prescribed in Lgr 11 and that they used The Big 5 to clarify the abilities that the topic addresses. All four LPPs have a common thread between grade 5 and 6 where some abilities are recorded again others are excluded and supplemented with new ones. Based on the results and the analysis, I came to the conclusion that both teachers teach the skills prescribed in Lgr 11 in the subject of physics in an open way of teaching, i.e. when students are active participants in the teaching. Combined teaching was used several times when the students e.g. had to try out for a given topic. Guided teaching was used only once in all four LPPs e.g. when the teachers prepare a list of concepts.

    Fulltekst (pdf)
    fulltext
  • 15.
    Wang, Yuli
    et al.
    KYH / Jiangsu University, Zhenjiang, China.
    Minh, Do-Quang
    KTH.
    Amberg, Gustav
    KTH.
    Dynamic wetting of viscoelastic droplets2015Inngår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 92, nr 4, artikkel-id 043002Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We conduct numerical experiments on spreading of viscoelastic droplets on a flat surface. Our work considers a Giesekus fluid characterized by a shear-thinning viscosity and an Oldroyd-B fluid, which is close to a Boger fluid with constant viscosity. Our results qualitatively agree with experimental observations in that both shear thinning and elasticity enhances contact line motion, and that the contact line motion of the Boger fluid obeys the Tanner-Voinov-Hoffman relation. Excluding inertia, the spreading speed shows strong dependence on rheological properties, such as the viscosity ratio between the solvent and the polymer suspension, and the polymeric relaxation time. We also discuss how elasticity can affect contact line motion. The molecular migration theory proposed in the literature is not able to explain the agreement between our simulations and experimental results.

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