15 research outputs found
Numerical analysis of acoustic scattering by a thin circular disk, with application to train-tunnel interaction noise
The sound generated by high speed trains can be exacerbated by the presence of trackside
structures. Tunnels are the principal structures that have a strong influence on the
noise produced by trains. A train entering a tunnel causes air to flow in and out of the
tunnel portal, forming a monopole source of low frequency sound ["infrasound"] whose
wavelength is large compared to the tunnel diameter. For the compact case, when the
tunnel diameter is small, incompressible flow theory can be used to compute the Green's
function that determines the monopole sound. However, when the infrasound is "shielded"
from the far field by a large "flange" at the tunnel portal, the problem of calculating the
sound produced in the far field is more complex. In this case, the monopole contribution
can be calculated in a first approximation in terms of a modified Compact Green's function,
whose properties are determined by the value at the center of a. disk (modelling the flange)
of a diffracted potential produced by a thin circular disk. In this thesis this potential is
calculated numerically. The scattering of sound by a thin circular disk is investigated using
the Finite Difference Method applied to the three dimensional Helmholtz equation subject
to appropriate boundary conditions on the disk. The solution is also used to examine the
unsteady force acting on the disk
An analysis of the micromechanics of the organ of Corti: significance of microfluid flow
We exploit novel modeling techniques to investigate the micromechanics of the organ of Corti (OC). Our first aim was to confirm that the tunnel of Corti (ToC) can sustain fluid wave propagation, as this may provide physiological grounds for the explanation of the cochlear amplifier by non-classical cochlear models. The experimental evidence is that OHC contraction induces oscillatory flow in the tunnel of Corti. The question we address is whether this oscillatory flow is produced by an actual fluid wave traveling in the ToC or is merely an oscillating flow with no spatial phase change. We hypothesize that the pillar cells must not present a significant barrier to flow into the tunnel of Corti if the latter can support sustainable traveling fluid waves in response to outer hair cell motion. We use both analytical and numerical models to investigate this hypothesis. The numerical model consists of a realistic three dimensional finite element model of ToC in the middle turn of the gerbil cochlea. The analytical estimates and numerical calculations give similar estimates for the impedance of the pillar cells to fluid flow into the tunnel of Corti. We conclude that the row of pillar cells does not significantly impede fluid exchange between ToC and the space of Nuel. The wavelength of the resulting fluid wave launched into the tunnel is 0.9 mm, which is similar, but somewhat larger, than the wavelength estimated for the classical traveling wave. We also found that this fluid wave propagates at least 1 wavelength before being significantly attenuated. Our results support the hypothesis that there is an additional source of longitudinal coupling, provided by the tunnel of Corti, as required in non-classical models of the cochlear amplifier. Our second aim was to assess the influence of the interstitial microfluid flow on the micromechanics of the organ of Corti. For this purpose, a finely resolved short section of the cochlea was simulated to study the fluid-elastic interaction. A modal analysis of the section was performed with and without cochlear fluid and the modal results were interpreted as the limiting case of wave propagation. The analysis results suggest that: (1) The long wave response is similar to the classical OC motion, with both arcuate and pectinate regions of the basilar membrane moving in phase and a pivoting of arch of Corti about the inner pillar foot. In this mode, however, the two inner rows of OHCs bend radially in phase while moving out of phase with the outermost row of OHCs. (2) The resonant response of the short cochlea section is characterized by a complex fluid-structure interaction mode, where the two regions of the basilar membrane move out of phase and fluid is moved between the tunnel of Corti, the interstitial spaces between the OHCs, and the outer tunnel. The outer hair cell rows move all in phase following the radial flow direction. A significant fluid motion was observed between the cylindrical cellular structures of the OC as the result of the structural displacement. This indicates that the flow of interstitial fluid avoids overpressuring the OC, and is responsible for driving cellular movements. (3) In both the long and short wave cases, fluid is squeezed radially, back and forth in the subtectorial space as a result of the bending motion of the reticular lamina in the region above the OHC heads. This causes a compression and expansion of the subtectorial space. This motion is consistent with experimentally observed motion during electrical stimulation experiments. Finally, we have developed a method to analyze periodic fluid-elastic waveguides with complex geometries, such as the cochlea. The method is a hybrid numerical-analytical based on the Floquet theory. We apply the method to two and three dimensional waveguides. We present and discuss the details of the method
Magasinets sköna, nya vÀrld : SÄ förÀndras journalistiken i klivet frÄn papper till surfplatta. En studie av Svenska Dagbladets Ipadmagasin Insikt
Medievanorna förĂ€ndras fort. Dagens mediekonsument krĂ€ver medier med ett âriktâ utbud, med rörliga bilderoch musik, ungefĂ€r som i den smarta mobilen. Och produkten ska vara möjlig att ta med sig överallt, för det Ă€r juvad den nya teknologin vant oss vid. Ipaden erbjuder just detta. MĂ„nga medieexperter menar att den Ă€r lösningenmed stort L för den krisande magasinsbranschen.Men hur förĂ€ndras journalistiken i klivet frĂ„n papper till Ipad? Det Ă€r vad min undersökning vill ge ett svar pĂ„.Den bygger pĂ„ ett nĂ€rstudium av de första Ă„tta utgĂ„vorna av Svenska Dagbladets Insikt, det mest utveckladeIpadmagasinet i Sverige just nu.Surfplattan Ă€r framför allt ett visuellt medium, men det ger ocksĂ„ en totalupplevelse, pĂ„ ett helt annat sĂ€tt Ă€n enpapperstidning. Flera sinnen stimuleras samtidigt, syn, hörsel, kĂ€nsel. Texter kan vara praktiskt taget hur lĂ„ngasom helst hĂ€r â men min studie visar att antalet bilder ökar Ă€nnu mer. I Insikt Ă€r det det rikt illustrerade ochtidlösa kulturreportaget med mĂ„nga interaktiva inslag som Ă€r sĂ€rskilt gynnat. Mycket tyder ocksĂ„ pĂ„ att arbetetmed den nya plattformen har inspirerat till ökad lekfullhet och kreativitet pĂ„ Svenska Dagbladets redaktion
Konsumentens upplevelse av interaktiv reklam
Tidigare studier pÄvisar att dagens marknadsföring inte Àr lika effektiv som förr, och behöver dÀrmed nyanseras. Marknadsförare Àr pÄ stÀndig jakt efter nya effektiva sÀtt att förmedla sina budskap pÄ. En av dessa nya fenomen Àr interaktiv reklam. Interaktiv reklam Àr ett innovativt verktyg, som Ànnu inte slagit rötter i medielandskapet och Àr dÀrmed ett fenomen som bör undersökas djupsinnigare. Syftet med denna studie Àr att förstÄ och undersöka fenomenet interaktiv reklam. FörstÄ dess potential samt vad konsumenter ser i mediet som de inte ser i traditionella medier. Problemet som ligger till grund för denna studie Àr att sjÀlva konstruktionen av reklam som finns tillgÀnglig i dag pÄminner mycket om varandra oavsett vilken plattform det gÀller. Detta medför att det finns stor risk för avtrubbning hos konsumenten. För att undersöka problemet har denna studie valt at stÀlla frÄgan: Hur upplever mediekommunikationsstudenter interaktiv reklam? Genom att angripa frÄgestÀllningen med en receptionsstudie med intervjuer som datainsamlingsmetod fick studien sitt syfte uppfyllt. Det genomfördes 14 stycken enskilda semistrukturerande intervjuer. Data analyserades med en tematisk analys med hjÀlp av Stuart Halls modell för olika tolkningssÀtt som teoretisk utgÄngspunkt. Studien resulterade i att interaktiv reklam var tilltalande och attityden var generellt positiv. Det studien kan konstatera Àr att interaktiv media har fÄtt en bra acceptans, och mÀnniskor Àr benÀgna att testa mediet. SÄledes behöver inte resultaten studien har fÄtt fram om att interaktiviteten fÄtt sÄ bra godkÀnnande ligga i enskilda individers resonemang utan rÀtteligen ligga i undermedvetet missnöje kring dagens övergripande reklam