4,141 research outputs found
Mixing by Swimming Algae
In this fluid dynamics video, we demonstrate the microscale mixing
enhancement of passive tracer particles in suspensions of swimming microalgae,
Chlamydomonas reinhardtii. These biflagellated, single-celled eukaryotes (10
micron diameter) swim with a "breaststroke" pulling motion of their flagella at
speeds of about 100 microns/s and exhibit heterogeneous trajectory shapes.
Fluorescent tracer particles (2 micron diameter) allowed us to quantify the
enhanced mixing caused by the swimmers, which is relevant to suspension feeding
and biogenic mixing. Without swimmers present, tracer particles diffuse slowly
due solely to Brownian motion. As the swimmer concentration is increased, the
probability density functions (PDFs) of tracer displacements develop strong
exponential tails, and the Gaussian core broadens. High-speed imaging (500 Hz)
of tracer-swimmer interactions demonstrates the importance of flagellar beating
in creating oscillatory flows that exceed Brownian motion out to about 5 cell
radii from the swimmers. Finally, we also show evidence of possible cooperative
motion and synchronization between swimming algal cells.Comment: 1 page, APS-DFD 2009 Gallery of Fluid Motio
Isomer triggering via nuclear excitation by electron capture
Triggering of long-lived nuclear isomeric states via coupling to the atomic
shells in the process of nuclear excitation by electron capture (NEEC) is
studied. NEEC occurring in highly-charged ions can excite the isomeric state to
a triggering level that subsequently decays to the ground state. We present
total cross sections for NEEC isomer triggering considering experimentally
confirmed low-lying triggering levels and reaction rates based on realistic
experimental parameters in ion storage rings. A comparison with other isomer
triggering mechanisms shows that, among these, NEEC is the most efficient.Comment: minor changes - updated to the final version; 4 pages, 1 figur
A Validated Reversed-Phase HPLC Method for the Determination of Atorvastatin Calcium in Tablets
A Reversed-Phase Liquid Chromatographic (RP-LC) assay method was developed for the quantitative determination of atorvastatin calcium in the presence of its degradation products. The assay involved an isocratic elution of atorvastatin calcium in a LiChroCARTR 250*4 mm HPLC Cartridge LiChrospherR 100 RP-18 (5 ÎŒm) column using a mobile phase consisting of 0.1% acetic acid solution: acetonitrile (45:55, v/v), pH = 3.8. The flow rate was 0.8 mL/min and the analytes monitored at 246 nm. The assay method was found to be linear from 8.13 to 23.77 ÎŒg/mL. All the validation parameters were within the acceptance range. The developed method was successfully applied to estimate the amount of atorvastatin calcium in tablets.Fil: Simionato, Laura Daniela. Universidad de Buenos Aires. Facultad de Farmacia y BioquĂmica. Departamento de TecnologĂa FarmacĂ©utica; ArgentinaFil: Ferello, L.. Universidad de Buenos Aires. Facultad de Farmacia y BioquĂmica. Departamento de TecnologĂa FarmacĂ©utica; ArgentinaFil: Stamer. S.. Universidad de Buenos Aires. Facultad de Farmacia y BioquĂmica. Departamento de TecnologĂa FarmacĂ©utica; ArgentinaFil: Repetto, M. F.. Universidad de Buenos Aires. Facultad de Farmacia y BioquĂmica. Departamento de TecnologĂa FarmacĂ©utica; ArgentinaFil: Zubata, P. D.. Universidad de Buenos Aires. Facultad de Farmacia y BioquĂmica. Departamento de TecnologĂa FarmacĂ©utica; ArgentinaFil: Segall, Adriana Ines. Universidad de Buenos Aires. Facultad de Farmacia y BioquĂmica. Departamento de TecnologĂa FarmacĂ©utica; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Houssay; Argentin
Estudo da eficĂĄcia dos pavimentos drenantes na redução do ruĂdo rodoviĂĄrio para condiçÔes seco e molhado
A experiĂȘncia portuguesa no domĂnio da avaliação dos nĂveis sonoros em diferentes tipos de
pavimentos e dos factores que os determinam ainda Ă© insuficiente, face Ă s exigĂȘncias europeias de qualidade ambiental. Assim, neste artigo estuda-se a eficĂĄcia dos pavimentos drenantes na redução do ruĂdo de trĂĄfego, quer na presença, quer na ausĂȘncia de precipitação.
No estudo consideram-se duas secçÔes consecutivas, integradas na A41/IC24, uma com
camada de desgaste em betĂŁo betuminoso drenante e a outra, com camada de desgaste em
betĂŁo betuminoso. A avaliação dos nĂveis sonoros em cada uma das secçÔes foi realizada pelo
MĂ©todo EstatĂstico de Passagem. Para as condiçÔes de ensaio consideradas â tipo de veĂculo, velocidade de ensaio, superfĂcie seca e molhada â verificou-se que o nĂvel de ruĂdo Ă© inferior na secção com camada drenante com a superfĂcie seca e molhada, embora os benefĂcios da sua utilização sejam reduzidos quando se trata de veĂculos pesados
Mobile Sound Recognition for the Deaf and Hard of Hearing
Human perception of surrounding events is strongly dependent on audio cues.
Thus, acoustic insulation can seriously impact situational awareness. We
present an exploratory study in the domain of assistive computing, eliciting
requirements and presenting solutions to problems found in the development of
an environmental sound recognition system, which aims to assist deaf and hard
of hearing people in the perception of sounds. To take advantage of smartphones
computational ubiquity, we propose a system that executes all processing on the
device itself, from audio features extraction to recognition and visual
presentation of results. Our application also presents the confidence level of
the classification to the user. A test of the system conducted with deaf users
provided important and inspiring feedback from participants.Comment: 25 pages, 8 figure
Critical Dynamics of the Contact Process with Quenched Disorder
We study critical spreading dynamics in the two-dimensional contact process
(CP) with quenched disorder in the form of random dilution. In the pure model,
spreading from a single particle at the critical point is
characterized by the critical exponents of directed percolation: in
dimensions, , , and . Disorder causes a
dramatic change in the critical exponents, to , , and . These exponents govern spreading following
a long crossover period. The usual hyperscaling relation, , is violated. Our results support the conjecture by Bramson, Durrett, and
Schonmann [Ann. Prob. {\bf 19}, 960 (1991)], that in two or more dimensions the
disordered CP has only a single phase transition.Comment: 11 pages, REVTeX, four figures available on reques
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