2,299 research outputs found
Electrically controlled topological micro cargo transportation
We demonstrate electrically controlled linear translation and precision positioning of a colloidal particle in a soft matter device. The basis of transportation is the time dependent electric field reconfiguration and manipulation of a topological line defect between two distinct hybrid aligned nematic liquid crystal domains having opposing tilt orientations. Deliberately tuning an applied voltage relative to a low threshold value (5.7 V at 1 kHz) permits defect trapping of the colloidal particle and allows subsequent control over the particle’s velocity and bidirectional linear movement over millimeter distances, without the need for externally imposed flow nor for lateral confining walls
Evolving mass spectra of the oxidized component of organic aerosol: results from aerosol mass spectrometer analyses of aged diesel emissions
International audienceThe species and chemistry responsible for secondary organic aerosol (SOA) formation remain highly uncertain. Laboratory studies of the oxidation of individual, high-flux SOA precursors do not lead to particles with mass spectra (MS) matching those of ambient aged organic material. Additionally, the complexity of real organic particles challenges efforts to identify their chemical origins. We have previously hypothesized that SOA can form from the atmospheric oxidation of a large suite of precursors with varying vapor pressures. Here, we support this hypothesis by using an aerosol mass spectrometer to track the chemical evolution of diesel exhaust as it is photochemically oxidized in an environmental chamber. With explicit knowledge of the condensed-phase MS of the primary emissions from our engine, we are able to decompose each recorded MS into contributing primary and secondary spectra throughout the experiment. We find that the SOA becomes increasingly oxidized as a function of time, quickly approaching a final MS that closely resembles that of ambient aged organic particulate matter. This observation is consistent with our hypothesis of an evolving suite of SOA precursors. Low vapor pressure, semi-volatile organic emissions can form condensable products with even a single generation of oxidation, resulting in an early-arising, relatively less-oxidized SOA. Continued gas-phase oxidation can form highly oxidized SOA in surprisingly young air masses via reaction mechanisms that can add multiple oxygen atoms per generation and result in products with sustained or increased reactivity toward OH
Triviality and the (Supersymmetric) See-Saw
For the D=5 Majorana neutrino mass operator to have a see-saw ultraviolet
completion that is viable up to the Planck scale, the see-saw scale is bounded
above due to triviality limits on the see-saw couplings. For supersymmetric
see-saw models, with realistic neutrino mass textures, we compare constraints
on the see-saw scale from triviality bounds, with those arising from
experimental limits on induced charged-lepton flavour violation, for both the
CMSSM and for models with split supersymmetry.Comment: 27 pages, 7 figures, references adde
Spitzer/IRS Imaging and Spectroscopy of the luminous infrared galaxy NGC 6052 (Mrk 297)
We present photometric and spectroscopic data of the interacting starburst
galaxy NGC 6052 obtained with the Spitzer Space Telescope. The mid-infrared
(MIR) spectra of the three brightest spatially resolved regions in the galaxy
are remarkably similar and are consistent with dust emission from young nearly
coeval stellar populations. Analysis of the brightest infrared region of the
system, which contributes ~18.5 % of the total 16\micron flux, indicates that
unlike similar off-nuclear infrared-bright regions found in Arp 299 or NGC
4038/9, its MIR spectrum is inconsistent with an enshrouded hot dust (T > 300K)
component. Instead, the three brightest MIR regions all display dust continua
of temperatures less than ~ 200K. These low dust temperatures indicate the dust
is likely in the form of a patchy screen of relatively cold material situated
along the line of sight. We also find that emission from polycyclic aromatic
hydrocarbons (PAHs) and the forbidden atomic lines is very similar for each
region. We conclude that the ionization regions are self-similar and come from
young (about 6 Myr) stellar populations. A fourth region, for which we have no
MIR spectra, exhibits MIR emission similar to tidal tail features in other
interacting galaxies.Comment: 20 pages in preprint form, estimated 7 pages in ApJ Aeptember 10,
2007, v666n 2 issue, six encapsulated postscript figure
The Cool ISM in S0 Galaxies. I. A Survey of Molecular Gas
Lenticular galaxies remain remarkably mysterious as a class. Observations to
date have not led to any broad consensus about their origins, properties and
evolution, though they are often thought to have formed in one big burst of
star formation early in the history of the Universe, and to have evolved
relatively passively since then. In that picture, current theory predicts that
stellar evolution returns substantial quantities of gas to the interstellar
medium; most is ejected from the galaxy, but significant amounts of cool gas
might be retained. Past searches for that material, though, have provided
unclear results. We present results from a survey of molecular gas in a
volume-limited sample of field S0 galaxies, selected from the Nearby Galaxies
Catalog. CO emission is detected from 78 percent of the sample galaxies. We
find that the molecular gas is almost always located inside the central few
kiloparses of a lenticular galaxy, meaning that in general it is more centrally
concentrated than in spirals. We combine our data with HI observations from the
literature to determine the total masses of cool and cold gas. Curiously, we
find that, across a wide range of luminosity, the most gas rich galaxies have
about 10 percent of the total amount of gas ever returned by their stars. That
result is difficult to understand within the context of either monolithic or
hierarchical models of evolution of the interstellar medium.Comment: 26 pages of text, 15 pages of tables, 10 figures. Accepted for
publication in the Astrophysical Journa
Discovery of Recent Star Formation in the Extreme Outer Regions of Disk Galaxies
We present deep Halpha images of three nearby late-type spiral galaxies
(NGC628, NGC1058 and NGC6946), which reveal the presence of HII regions out to,
and beyond, two optical radii (defined by the 25th B-band isophote). The
outermost HII regions appear small, faint and isolated, compared to their inner
disk counterparts, and are distributed in organized spiral arm structures,
likely associated with underlying HI arms and faint stellar arms. The
relationship between the azimuthally--averaged Halpha surface brightness
(proportional to star formation rate per unit area) and the total gas surface
density is observed to steepen considerably at low gas surface densities. We
find that this effect is largely driven by a sharp decrease in the covering
factor of star formation at large radii, and not by changes in the rate at
which stars form locally. An azimuthally--averaged analysis of the
gravitational stability of the disk of NGC6946 reveals that while the existence
of star formation in the extreme outer disk is consistent with the Toomre-Q
instability model, the low rates observed are only compatible with the model
when a constant gaseous velocity dispersion is assumed. We suggest that
observed behaviour could also be explained by a model in which the star
formation rate has an intrinsic dependence on the azimuthally-averaged gas
volume density, which decreases rapidly in the outer disk due to the vertical
flaring of the gas layer.Comment: 10 pages, 2 embedded postscript files, 3 jpeg images; accepted for
publication in ApJ Letter
Comparison of Deconvolution Software: A User Point of View—Part 2
Deconvolution is an image processing technique that restores the effective object representation [3] [4], allowing to improve images analysis steps such as segmentation [1] or colocalization study [2]. We performed several deconvolution tests on different kinds of datasets. The methodology has been reported in Part 1. Evaluation criteria and results are reported here. References A. Chomik, A. Dieterlen, C. Xu, O. Haeberlé, J.J. Meyer, S. Jacquey, "Quantification in Optical Sectioning Microscopy: A Comparison of Some Deconvolution Algorithms in View of 3D Image Segmentation," Journal of Optics, vol. 28, no. 6, pp. 225-233, December 1997. L. Landmann, "Deconvolution Improves Colocalization Analysis of Multiple Fluorochromes in 3D Confocal Data Sets more than Filtering Techniques," Journal of Microscopy, vol. 208, no. 2, pp. 134-147, November 2002. J.-B. Sibarita, "Deconvolution Microscopy," Advances in Biochemical Engineering/Biotechnology, vol. 95, pp. 201-243, 2005. W. Wallace, L.H. Schaefer, J.R. Swedlow, "A Workingperson's Guide to Deconvolution in Light Microscopy," BioTechniques, vol. 31, no. 5, pp. 1076-1097, November 2001
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