The acoustic force density acting on inhomogeneous fluids in acoustic fields

We present a theory for the acoustic force density acting on inhomogeneous fluids in acoustic fields on time scales that are slow compared to the acoustic oscillation period. The acoustic force density depends on gradients in the density and compressibility of the fluid. For microfluidic systems, the theory predicts a relocation of the inhomogeneities into stable field-dependent configurations, which are qualitatively different from the horizontally layered configurations due to gravity. Experimental validation is obtained by confocal imaging of aqueous solutions in a glass-silicon microchip.Comment: RevTex, 5 pages, 3 eps figure

IT and telecom companies in Kista Science City, Northern Stockholm

The Kista area north of Stockholm is a symbol of Sweden’s IT and telecom sector, which has great importance for the economy and working life. The report gives a current, empirically founded description of the IT sector in Kista (including the districts Akalla and Husby), which to a high extent previously has not been available. What do the establishments in Kista look like and what are the relations between them? The management of one hundred IT and telecom establishments in Kista with up to 200 employees have answered a substantial number of survey questions about their activities, their staff and about Kista. The report is descriptive and includes a short description of Kista’s history from the ideas of a city with an integration of work, housing and services until today’s Kista Science City, the year of establishment, number and size of the IT establishments in Kista and their activities. Some results in brief are: • Most of the companies have developed during the last five to ten years. • They are to a very high degree focused on IT and telecom. The most common activity is consulting followed by production of software, R&D and commerce. • More than half of the establishments have an exchange of experiences with other companies in Kista, and almost half of them are involved in strategic cooperation within e.g. development, production and marketing. • Quite a few outsource IT activities to other companies and work as subcontractors to them, but only a limited part of the contracts are with companies in Kista. The networks are regional and international rather than local. • About a quarter cooperate with interactive media companies in Stockholm. • The managements are throughout satisfied with Kista. On all the five factors they see as most important for their operations, Kista comes out well: communications, telecom, premises, competent staff and customers. Kista also comes out well on the criterion proximity to university; although few regard this as important, which is discussed in the report. • One fifth of the employees are women and the top manager is a woman in less then ten per cent of the establishments. • The average age of employees is 38 years. • The staff is well educated, almost 70 percent have three years university education or more. Still, managements view learning on the establishment as the most important source of skills. Perhaps university education is taken for granted.

The sulfur budget of the troposphere

A one dimensional photochemical tropospheric model was used to calculate the vertical profiles of tropospheric species. Particular attention is focused on the recent inclusion of the chemistry of the sulfur group, which consists of 13 species involving a total of 45 chemical reactions. It is found that the chemistry of the sulfur species, because it is largely anthropogenic, plays an increasingly important role in the distribution of tropospheric gases. The calculated vertical profiles were compared to available measurements and generally found to be in good agreement

Characterization of Acoustic Streaming in Gradients of Density and Compressibility

Suppression of boundary-driven Rayleigh streaming has recently been demonstrated for fluids of spatial inhomogeneity in density and compressibility owing to the competition between the boundary-layer-induced streaming stress and the inhomogeneity-induced acoustic body force. Here we characterize acoustic streaming by general defocusing particle tracking inside a half-wavelength acoustic resonator filled with two miscible aqueous solutions of different density and speed of sound controlled by the mass fraction of solute molecules. We follow the temporal evolution of the system as the solute molecules become homogenized by diffusion and advection. Acoustic streaming rolls is suppressed in the bulk of the microchannel for 70-200 seconds dependent on the choice of inhomogeneous solutions. From confocal measurements of the concentration field of fluorescently labelled Ficoll solute molecules, we conclude that the temporal evolution of the acoustic streaming depends on the diffusivity and the initial distribution of these molecules. Suppression and deformation of the streaming rolls are observed for inhomogeneities in the solute mass fraction down to 0.1 %.Comment: RevTex, pdfLaTex, 10 pages, 10 pdf figure

Acoustic streaming and its suppression in inhomogeneous fluids

We present a theoretical and experimental study of boundary-driven acoustic streaming in an inhomogeneous fluid with variations in density and compressibility. In a homogeneous fluid this streaming results from dissipation in the boundary layers (Rayleigh streaming). We show that in an inhomogeneous fluid, an additional non-dissipative force density acts on the fluid to stabilize particular inhomogeneity configurations, which markedly alters and even suppresses the streaming flows. Our theoretical and numerical analysis of the phenomenon is supported by ultrasound experiments performed with inhomogeneous aqueous iodixanol solutions in a glass-silicon microchip.Comment: 6 pages, 3 pdf figures, RevTex 4-

Influencing factors on petrography interpretations in provenance research – a case-study review

The use of framework petrography is a common initial step in provenance research of sand and sandstone. The data tend to be interpreted based on the three main components quartz, feldspar, and lithic fragments. Surprisingly often, this is done without taking other influencing factors than the tectonic setting of the catchment and/or the surroundings of the depositional basin into account. Based on a database of 14 studies with approximately 900 petrographic data points from sand and sandstone, this study demonstrates quantitative effects on the apparent composition resulting from both geological and non-geological biases. The study illustrates sandstone-classification differences based on different specifications of the three end-members quartz, feldspar, and lithic or rock fragments, how the point-counting method can affect the apparent petrographic composition of sandstone, how sorting and facies bias may be differentiated from a climate or provenance signal, and how bias due to diagenetic effects can be minimised. In conclusion, both geological and non-geological biases should be considered for provenance studies that include petrographic data.publishedVersio

Evaluating Switching GARCH Volatility Forecasts During the Recent Financial Crisis

Forecasting volatility is a fundamental topic in in both academic and applied financial economics. Different GARCH-specifications are by far the most popular model based approach used for this purpose. This thesis evaluates the forecast accuracy of some specific GARCH-models; GARCH, EGARCH, APGARCH and MRS-GARCH. The primary purpose of the essay is to investigate whether the more flexible two-regime MRS-GARCH model outperforms the more conventional one-regime GARCH models in a very volatile time period during the recent financial crises. The evaluation period stretches from the day when Lehman Brothers went bankrupt and one year ahead. Each model is evaluated using two indexes with different characteristics; the Standard & Poor 500 and the Bombay Sensex index. The result shows that the MRS-GARCH models are superior in predictive ability on S&P500 compared to the other tested models. Conversely, the overall relative performance accuracy of the BSE is less clear-cut since none of the tested models seem to perform particularly well. Generally, the results indicate that the MRS-GARCH provides better forecasts on S&P 500 compared to the other models and that no forecast can be distinguished as entirely superior on the BSE

Provenance of late Palaeozoic sediments in the southern Patagonian Andes

U-Pb-Datierungen von detritischen Zirkonen des sedimentären Grundgebirges der Anden (47-51°S) zeigen maximale Ablagerungsalter von Devon - Frühkarbon bis Spätkarbon - Frühperm an. Die hauptsächlichen Liefergesteine waren felsisch, metasedimentär und metamorph, und das Material wurde in der Kruste vor der Ablagerung recycelt wie angedeutet von KL von Quarz, Turmalin-Chemismus, Gesamtgesteinselement- und Sr-Nd-isotop-Chemie, und U-Pb Alter detritischer Zirkone. U-Pb-Alter und Hf-Isotopie von Einzelzirkonen zeigen, dass die ursprünglichen Hauptquellen das argentinsche Patagonien und die Sierra de la Ventana, das südliche Afrika, die Ostantarktis und das Falklandplateau waren. Die ?permischen Sedimente hatten felsische, magmatische Hauptquellen mit kontinentalem Ursprung und die Sedimente hatten kurze Transportwege. Mit Hilfe der obengenannten Daten stützt diese Studie einen Beginn von Subduktion am pazifischen Kontinentalrand Gondwanas im Spätkarbon

Effects of Multiple Scattering and Surface Albedo on the Photochemistry of the Troposphere

A one-dimensional photochemical model of the troposphere containing the species of the nitrogen, oxygen, carbon, hydrogen, and sulfur families has been developed and used to investigate the vertical profiles and the natural (including atmospheric chemical reactions) and anthropogenic sources and sinks of these species. The species continuity equations are solved numerically applying prescribed boundary conditions. The vertical flux is simulated by use of the parameterized eddy diffusion coefficients. Heterogeneous losses (e.g. rainout, gas-to-particle chemistry, and dry deposition), are parameterized to make calculated profiles consistent with measurements. The photochemical model is coupled to a radiative transfer model that calculates the radiation field due to the incoming solar radiation which initiates much of the photochemistry of the troposphere. Comparisons of vertical profiles of tropospheric species are made between the Leighton approximation, widely used in most tropospheric models, and the detailed radiative transfer matrix inversion model used in this study. The radiative transfer code includes the effects of multiple scattering due to molecules and aerosols, pure absorption and surface albedo on the transfer of incoming solar radiation. The results indicate that significant differences exist for several key photolysis frequencies and species number density profiles between the Leighton approximation and the profiles generated with the more detailed radiative transfer matrix inversion technique used in this study. Most species show enhanced vertical profiles when the more realistic treatment of the incoming solar radiation field is included. Furthermore, most species increase in concentration as a function of increasing surface albedo. A few species, notably ozone, exhibit decreased levels of concentration when the realistic radiative transfer model is used. The effect of the detailed treatment of incoming solar radiation on the photochemistry of the troposphere is discussed