1,656 research outputs found
Far-Field Plasmonic Resonance Enhanced Nano-Particle Image Velocimetry within a Micro Channel
In this paper, a novel far-field plasmonic resonance enhanced
nanoparticle-seeded Particle Image Velocimetry (nPIV) has been demonstrated to
measure the velocity profile in a micro channel. Chemically synthesized silver
nanoparticles have been used to seed the flow in the micro channel. By using
Discrete Dipole Approximation (DDA), plasmonic resonance enhanced light
scattering has been calculated for spherical silver nanoparticles with
diameters ranging from 15nm to 200nm. Optimum scattering wavelength is
specified for the nanoparticles in two media: water and air. The
diffraction-limited plasmonic resonance enhanced images of silver nanoparticles
at different diameters have been recorded and analyzed. By using standard PIV
techniques, the velocity profile within the micro channel has been determined
from the images.Comment: submitted to Review of Scientific Instrument
Analytical and experimental investigations of dual-plane PIV
In its 'classical' form particle image velocimetry (PIV) extracts two components of the flow velocity vector by measuring the displacement of tracer particles within a double-pulsed laser light sheet. The method described in this paper is based on the additional recording of a third exposure of the tracer particles in a parallel light sheet, which is slightly displaced with respect to the first one. The particle images resulting from these three exposures are stored on separate frames. The locations of the correlation peaks, as obtained by cross-correlation methods, are used to determine the projections of the velocity vectors onto the plane between both light sheets. In the manner described below, the amplitudes of these peaks are used to obtain information about the velocity component perpendicular to the light sheet planes. The mathematical background of this method is described in the paper. Numerical simulations show the influence of the main parameters (e.g. light sheet thickness, light sheet displacement and out-of-plane component) on the resolution and reliability of the new method. Two different recording procedures and their results will be shown to demonstrate the ease of operation when applying this technique to liquid flows
Improved synthesis of 4-[18F]fluoro-m-hydroxyphenethylguanidine using an iodonium ylide precursor
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/151961/1/jlcr3791.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151961/2/jlcr3791_am.pd
Extraction of coherent structures in a rotating turbulent flow experiment
The discrete wavelet packet transform (DWPT) and discrete wavelet transform
(DWT) are used to extract and study the dynamics of coherent structures in a
turbulent rotating fluid. Three-dimensional (3D) turbulence is generated by
strong pumping through tubes at the bottom of a rotating tank (48.4 cm high,
39.4 cm diameter). This flow evolves toward two-dimensional (2D) turbulence
with increasing height in the tank. Particle Image Velocimetry (PIV)
measurements on the quasi-2D flow reveal many long-lived coherent vortices with
a wide range of sizes. The vorticity fields exhibit vortex birth, merger,
scattering, and destruction. We separate the flow into a low-entropy
``coherent'' and a high-entropy ``incoherent'' component by thresholding the
coefficients of the DWPT and DWT of the vorticity fields. Similar thresholdings
using the Fourier transform and JPEG compression together with the Okubo-Weiss
criterion are also tested for comparison. We find that the DWPT and DWT yield
similar results and are much more efficient at representing the total flow than
a Fourier-based method. Only about 3% of the large-amplitude coefficients of
the DWPT and DWT are necessary to represent the coherent component and preserve
the vorticity probability density function, transport properties, and spatial
and temporal correlations. The remaining small amplitude coefficients represent
the incoherent component, which has near Gaussian vorticity PDF, contains no
coherent structures, rapidly loses correlation in time, and does not contribute
significantly to the transport properties of the flow. This suggests that one
can describe and simulate such turbulent flow using a relatively small number
of wavelet or wavelet packet modes.Comment: experimental work aprox 17 pages, 11 figures, accepted to appear in
PRE, last few figures appear at the end. clarifications, added references,
fixed typo
Inactivation of Genes for Antigenic Variation in the Relapsing Fever Spirochete \u3ci\u3eBorrelia hermsii\u3c/i\u3e Reduces Infectivity in Mice and Transmission by Ticks
Borrelia hermsii, a causative agent of relapsing fever of humans in western North America, is maintained in enzootic cycles that include small mammals and the tick vector Ornithodoros hermsi. In mammals, the spirochetes repeatedly evade the host’s acquired immune response by undergoing antigenic variation of the variable major proteins (Vmps) produced on their outer surface. This mechanism prolongs spirochete circulation in blood, which increases the potential for acquisition by fast-feeding ticks and therefore perpetuation of the spirochete in nature. Antigenic variation also underlies the relapsing disease observed when humans are infected. However, most spirochetes switch off the bloodstream Vmp and produce a different outer surface protein, the variable tick protein (Vtp), during persistent infection in the tick salivary glands. Thus the production of Vmps in mammalian blood versus Vtp in ticks is a dominant feature of the spirochete’s alternating life cycle. We constructed two mutants, one which was unable to produce a Vmp and the other was unable to produce Vtp. The mutant lacking a Vmp constitutively produced Vtp, was attenuated in mice, produced lower cell densities in blood, and was unable to relapse in animals after its initial spirochetemia. This mutant also colonized ticks and was infectious by tick-bite, but remained attenuated compared to wild-type and reconstituted spirochetes. The mutant lacking Vtp also colonized ticks but produced neither Vtp nor a Vmp in tick salivary glands, which rendered the spirochete noninfectious by tick bite. Thus the ability of B. hermsii to produce Vmps prolonged its survival in blood, while the synthesis of Vtp was essential for mammalian infection by the bite of its tick vector
Binding of [ 3 H]mazindol to cardiac norepinephrine transporters: kinetic and equilibrium studies
The norepinephrine transporter (NET) is the carrier that drives the neuronal norepinephrine uptake mechanism (uptake 1 ) in mammalian hearts. The radioligand [ 3 H]mazindol binds with high affinity to NET. In this study, the kinetics of [ 3 H]mazindol binding to NET were measured using a rat heart membrane preparation. Results from these studies were used to set up saturation binding assays designed to measure cardiac NET densities ( B max ) and competitive inhibition assays designed to measure inhibitor binding affinities ( K I ) for NET. Saturation binding assays measured NET densities in rat, rabbit, and canine hearts. Assay reproducibility was assessed and the effect of NaCl concentration on [ 3 H]mazindol binding to NET was studied using membranes from rat and canine hearts. Specificity of [ 3 H]mazindol binding to NET was determined in experiments in which the neurotoxin 6-hydroxydopamine (6-OHDA) was used to selectively destroy cardiac sympathetic nerve terminals in rats. Competitive inhibition studies measured K I values for several NET inhibitors and substrates. In kinetic studies using rat heart membranes, [ 3 H]mazindol exhibited a dissociation rate constant k off =0.0123±0.0007 min −1 and an association rate constant k on =0.0249±0.0019 nM −1 min −1 . In saturation binding assays, [ 3 H]mazindol binding was monophasic and saturable in all cases. Increasing the concentration of NaCl in the assay buffer increased binding affinity significantly, while only modestly increasing B max . Injections of 6-OHDA in rats decreased measured cardiac NET B max values in a dose-dependent manner, verifying that [ 3 H]mazindol binds specifically to NET from sympathetic nerve terminals. Competitive inhibition studies provided NET inhibitor and substrate K I values consistent with previously reported values. These studies demonstrate the high selectivity of [ 3 H]mazindol binding for the norepinephrine transporter in membrane preparations from mammalian hearts.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46313/1/210_2004_Article_949.pd
Transition phenomena in unstably stratified turbulent flows
We study experimentally and theoretically transition phenomena caused by the
external forcing from Rayleigh-Benard convection with the large-scale
circulation (LSC) to the limiting regime of unstably stratified turbulent flow
without LSC whereby the temperature field behaves like a passive scalar. In the
experiments we use the Rayleigh-B\'enard apparatus with an additional source of
turbulence produced by two oscillating grids located nearby the side walls of
the chamber. When the frequency of the grid oscillations is larger than 2 Hz,
the large-scale circulation (LSC) in turbulent convection is destroyed, and the
destruction of the LSC is accompanied by a strong change of the mean
temperature distribution. However, in all regimes of the unstably stratified
turbulent flow the ratio varies slightly (even in the range
of parameters whereby the behaviour of the temperature field is different from
that of the passive scalar). Here are the integral scales of
turbulence along x, y, z directions, T and \theta are the mean and fluctuating
parts of the fluid temperature. At all frequencies of the grid oscillations we
have detected the long-term nonlinear oscillations of the mean temperature. The
theoretical predictions based on the budget equations for turbulent kinetic
energy, turbulent temperature fluctuations and turbulent heat flux, are in
agreement with the experimental results.Comment: 14 pages, 14 figures, REVTEX4-1, revised versio
Genome-Wide Association Study Identifies Loci for Liver Enzyme Concentrations in Mexican Americans: The GUARDIAN Consortium.
ObjectivePopulations of Mexican American ancestry are at an increased risk for nonalcoholic fatty liver disease. The objective of this study was to determine whether loci in known and novel genes were associated with variation in aspartate aminotransferase (AST) (n = 3,644), alanine aminotransferase (ALT) (n = 3,595), and gamma-glutamyl transferase (GGT) (n = 1,577) levels by conducting the first genome-wide association study (GWAS) of liver enzymes, which commonly measure liver function, in individuals of Mexican American ancestry.MethodsLevels of AST, ALT, and GGT were determined by enzymatic colorimetric assays. A multi-cohort GWAS of individuals of Mexican American ancestry was performed. Single-nucleotide polymorphisms (SNP) were tested for association with liver outcomes by multivariable linear regression using an additive genetic model. Association analyses were conducted separately in each cohort, followed by a nonparametric meta-analysis.ResultsIn the PNPLA3 gene, rs4823173 (P = 3.44 × 10-10 ), rs2896019 (P = 7.29 × 10-9 ), and rs2281135 (P = 8.73 × 10-9 ) were significantly associated with AST levels. Although not genome-wide significant, these same SNPs were the top hits for ALT (P = 7.12 × 10-8 , P = 1.98 × 10-7 , and P = 1.81 × 10-7 , respectively). The strong correlation (r2 = 1.0) for these SNPs indicated a single hit in the PNPLA3 gene. No genome-wide significant associations were found for GGT.ConclusionsPNPLA3, a locus previously identified with ALT, AST, and nonalcoholic fatty liver disease in European and Japanese GWAS, is also associated with liver enzymes in populations of Mexican American ancestry
Robust cell tracking in epithelial tissues through identification of maximum common subgraphs
Tracking of cells in live-imaging microscopy videos of epithelial sheets is a powerful tool for investigating fundamental processes in embryonic development. Characterizing cell growth, proliferation, intercalation and apoptosis in epithelia helps us to understand how morphogenetic processes such as tissue invagination and extension are locally regulated and controlled. Accurate cell tracking requires correctly resolving cells entering or leaving the field of view between frames, cell neighbour exchanges, cell removals and cell divisions. However, current tracking methods for epithelial sheets are not robust to large morphogenetic deformations and require significant manual interventions. Here, we present a novel algorithm for epithelial cell tracking, exploiting the graph-theoretic concept of a ‘maximum common subgraph’ to track cells between frames of a video. Our algorithm does not require the adjustment of tissue-specific parameters, and scales in sub-quadratic time with tissue size. It does not rely on precise positional information, permitting large cell movements between frames and enabling tracking in datasets acquired at low temporal resolution due to experimental constraints such as phototoxicity. To demonstrate the method, we perform tracking on the Drosophila embryonic epidermis and compare cell–cell rearrangements to previous studies in other tissues. Our implementation is open source and generally applicable to epithelial tissues
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