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

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-

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.

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

Benchmarking Implementations of Functional Languages with ``Pseudoknot'', a Float-Intensive Benchmark

Over 25 implementations of different functional languages are benchmarked using the same program, a floatingpoint intensive application taken from molecular biology. The principal aspects studied are compile time and execution time for the various implementations that were benchmarked. An important consideration is how the program can be modified and tuned to obtain maximal performance on each language implementation.\ud With few exceptions, the compilers take a significant amount of time to compile this program, though most compilers were faster than the then current GNU C compiler (GCC version 2.5.8). Compilers that generate C or Lisp are often slower than those that generate native code directly: the cost of compiling the intermediate form is normally a large fraction of the total compilation time.\ud There is no clear distinction between the runtime performance of eager and lazy implementations when appropriate annotations are used: lazy implementations have clearly come of age when it comes to implementing largely strict applications, such as the Pseudoknot program. The speed of C can be approached by some implemtations, but to achieve this performance, special measures such as strictness annotations are required by non-strict implementations.\ud The benchmark results have to be interpreted with care. Firstly, a benchmark based on a single program cannot cover a wide spectrum of 'typical' applications.j Secondly, the compilers vary in the kind and level of optimisations offered, so the effort required to obtain an optimal version of the program is similarly varied

Ultrasound-induced acoustophoretic motion of microparticles in three dimensions

We derive analytical expressions for the three-dimensional (3D) acoustophoretic motion of spherical microparticles in rectangular microchannels. The motion is generated by the acoustic radiation force and the acoustic streaming-induced drag force. In contrast to the classical theory of Rayleigh streaming in shallow, infinite, parallel-plate channels, our theory does include the effect of the microchannel side walls. The resulting predictions agree well with numerics and experimental measurements of the acoustophoretic motion of polystyrene spheres with nominal diameters of 0.537 um and 5.33 um. The 3D particle motion was recorded using astigmatism particle tracking velocimetry under controlled thermal and acoustic conditions in a long, straight, rectangular microchannel actuated in one of its transverse standing ultrasound-wave resonance modes with one or two half-wavelengths. The acoustic energy density is calibrated in situ based on measurements of the radiation dominated motion of large 5-um-diam particles, allowing for quantitative comparison between theoretical predictions and measurements of the streaming induced motion of small 0.5-um-diam particles.Comment: 13 pages, 8 figures, Revtex 4.

Diving with microparticles in acoustic fields

Sound can move particles. A good example of this phenomenon is the Chladni plate, in which an acoustic wave is induced in a metallic plate and particles migrate to the nodes of the acoustic wave. For several years, acoustophoresis has been used to manipulate microparticles in microscopic scales. In this fluid dynamics video, submitted to the 30th Annual Gallery of Fluid Motion, we show the basic mechanism of the technique and a simple way of visualize it. Since acoustophoretic phenomena is essentially a three-dimensional effect, we employ a simple technique to visualize the particles in 3D. The technique is called Astigmatism Particle Tracking Velocimetry and it consists in the use of cylindrical lenses to induce a deformation in the particle shape, which will be then correlated with its distance from the observer. With this method we are able to dive with the particles and observe in detail particle motion that would otherwise be missed. The technique not only permits visualization but also precise quantitative measurements that can be compared with theory and simulations.Comment: Fluid dynamics video for the 30th Annual Gallery of Fluid Motion, Entry #84160 65th Annual Meeting of the American Physical Society, Division of Fluid Dynamics San Diego, CA, Nov 201