3,293 research outputs found
Planar digital nanoliter dispensing system based on thermocapillary actuation
We provide guidelines for the design and operation of a planar digital nanodispensing system based on
thermocapillary actuation. Thin metallic microheaters embedded within a chemically patterned glass
substrate are electronically activated to generate and control 2D surface temperature distributions
which either arrest or trigger liquid flow and droplet formation on demand. This flow control is
a consequence of the variation of a liquid’s surface tension with temperature, which is used to draw
liquid toward cooler regions of the supporting substrate. A liquid sample consisting of several
microliters is placed on a flat rectangular supply cell defined by chemical patterning. Thermocapillary
switches are then activated to extract a slender fluid filament from the cell and to divide the filament into
an array of droplets whose position and volume are digitally controlled. Experimental results for the
power required to extract a filament and to divide it into two or more droplets as a function of
geometric and operating parameters are in excellent agreement with hydrodynamic simulations. The
capability to dispense ultralow volumes onto a 2D substrate extends the functionality of microfluidic
devices based on thermocapillary actuation previously shown effective in routing and mixing nanoliter
liquid samples on glass or silicon substrates
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Organic aerosol formation downwind from the Deepwater Horizon oil spill.
A large fraction of atmospheric aerosols are derived from organic compounds with various volatilities. A National Oceanic and Atmospheric Administration (NOAA) WP-3D research aircraft made airborne measurements of the gaseous and aerosol composition of air over the Deepwater Horizon (DWH) oil spill in the Gulf of Mexico that occurred from April to August 2010. A narrow plume of hydrocarbons was observed downwind of DWH that is attributed to the evaporation of fresh oil on the sea surface. A much wider plume with high concentrations of organic aerosol (>25 micrograms per cubic meter) was attributed to the formation of secondary organic aerosol (SOA) from unmeasured, less volatile hydrocarbons that were emitted from a wider area around DWH. These observations provide direct and compelling evidence for the importance of formation of SOA from less volatile hydrocarbons
A low optical depth region in the inner disk of the HerbigAe star HR5999
Circumstellar disks surrounding young stars are known to be the birthplaces
of planets, and the innermost astronomical unit is of particular interest. We
present new long-baseline spectro-interferometric observations of the HerbigAe
star, HR5999, obtained in the H and K bands with the AMBER instrument at the
VLTI, and aim to produce near-infrared images at the sub-AU spatial scale. We
spatially resolve the circumstellar material and reconstruct images using the
MiRA algorithm. In addition, we interpret the interferometric observations
using models that assume that the near-infrared excess is dominated by the
emission of a circumstellar disk. We compare the images reconstructed from the
VLTI measurements to images obtained using simulated model data. The K-band
image reveals three main elements: a ring-like feature located at ~0.65 AU, a
low surface brightness region inside, and a central spot. At the maximum
angular resolution of our observations (1.3 mas), the ring is resolved while
the central spot is only marginally resolved, preventing us from revealing the
exact morphology of the circumstellar environment. We suggest that the ring
traces silicate condensation, i.e., an opacity change, in a circumstellar disk
around HR 5999. We build a model that includes a ring at the silicate
sublimation radius and an inner disk of low surface brightness responsible for
a large amount of the near-infrared continuum emission. The model successfully
fits the SED, visibilities, and closure phases, and provides evidence of a low
surface brightness region inside the silicate sublimation radius. This study
provides additional evidence that in HerbigAe stars, there is material in a low
surface brightness region, probably a low optical depth region, located inside
the silicate sublimation radius and of unknown nature.Comment: 11 pages, 10 figure
Simultaneous radio-interferometric and high-energy TeV observations of the gamma-ray blazar Mkn 421
The TeV-emitting BL Lac object Mkn 421 was observed with very long baseline
interferometry (VLBI) at three closely-spaced epochs one-month apart in
March-April 1998. The source was also monitored at very-high gamma-ray energies
(TeV measurements) during the same period in an attempt to search for
correlations between TeV variability and the evolution of the radio morphology
on parsec scales. While the VLBI maps show no temporal changes in the Mkn 421
VLBI jet, there is strong evidence of complex variability in both the total and
polarized fluxes of the VLBI core of Mkn 421 and in its spectrum over the
two-month span of our data. The high-energy measurements indicate that the
overall TeV activity of the source was rising during this period, with a
gamma-ray flare detected just three days prior to our second VLBI observing
run. Although no firm correlation can be established, our data suggest that the
two phenomena (TeV activity and VLBI core variability) are connected, with the
VLBI core at 22 GHz being the self-absorbed radio counterpart of synchrotron
self-Compton (SSC) emission at high energies. Based on the size of the VLBI
core, we could derive an upper limit of 0.1 pc (3 x 10**17 cm) for the
projected size of the SSC zone. This determination is the first model-free
estimate of the size of the gamma-ray emitting region in a blazar.Comment: 12 pages, 9 figures, accepted for publication in Astronomy &
Astrophysic
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Agricultural fires in the southeastern US during SEAC(4)RS: Emissions of trace gases and particles and evolution of ozone, reactive nitrogen, and organic aerosol
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Airborne measurements of western U.S. wildfire emissions: Comparison with prescribed burning and air quality implications
Wildfires emit significant amounts of pollutants that degrade air quality. Plumes from three wildfires in the western U.S. were measured from aircraft during the Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS) and the Biomass Burning Observation Project (BBOP), both in summer 2013. This study reports an extensive set of emission factors (EFs) for over 80 gases and 5 components of submicron particulate matter (PM1) from these temperate wildfires. These include rarely, or never before, measured oxygenated volatile organic compounds and multifunctional organic nitrates. The observed EFs are compared with previous measurements of temperate wildfires, boreal forest fires, and temperate prescribed fires. The wildfires emitted high amounts of PM1 (with organic aerosol (OA) dominating the mass) with an average EF that is more than 2 times the EFs for prescribed fires. The measured EFs were used to estimate the annual wildfire emissions of carbon monoxide, nitrogen oxides, total nonmethane organic compounds, and PM1 from 11 western U.S. states. The estimated gas emissions are generally comparable with the 2011 National Emissions Inventory (NEI). However, our PM1 emission estimate (1530 ± 570 Gg yr-1) is over 3 times that of the NEI PM2.5 estimate and is also higher thanthe PM2.5 emitted from all other sources in these states in the NEI. This study indicates that the source of OA from biomass burning in the western states is significantly underestimated. In addition, our results indicate that prescribed burning may be an effective method to reduce fine particle emissions
Genetic and biochemical analyses of chromosome and plasmid gene homologues encoding ICL and ArCP domains in Vibrioanguillarum strain 775
Anguibactin, the siderophore produced by Vibrio anguillarum 775 is synthesized from 2,3-dihydroxybenzoic acid (DHBA), cysteine and hydroxyhistamine via a nonribosomal peptide synthetase (NRPS) mechanism. Most of the genes encoding anguibactin biosynthetic proteins are harbored by the pJM1 plasmid. In this work we report the identification of a homologue of the plasmid-encoded angB on the chromosome of strain 775. The product of both genes harbor an isochorismate lyase (ICL) domain that converts isochorismic acid to 2,3-dihydro-2,3-dihydroxybenzoic acid, one of the steps of DHBA synthesis. We show in this work that both ICL domains are functional in the production of DHBA in V. anguillarum as well as in E. coli. Substitution by alanine of the aspartic acid residue in the active site of both ICL domains completely abolishes their isochorismate lyase activity in vivo. The two proteins also carry an aryl carrier protein (ArCP) domain. In contrast with the ICL domains only the plasmid encoded ArCP can participate in anguibactin production as determined by complementation analyses and site-directed mutagenesis in the active site of the plasmid encoded protein, S248A. The site-directed mutants, D37A in the ICL domain and S248A in the ArCP domain of the plasmid encoded AngB were also tested in vitro and clearly show the importance of each residue for the domain function and that each domain operates independently.
High-Redshift Starbursting Dwarf Galaxies Revealed by GRB Afterglows
We present a study of 15 long-duration gamma-ray burst (GRB) host galaxies at
z>2. The GRBs are selected with available early-time afterglow spectra in order
to compare interstellar medium (ISM) absorption-line properties with stellar
properties of the host galaxies. In addition to five previously studied hosts,
we consider new detections for the host galaxies of GRB050820 and GRB060206 and
place 2-sigma upper limits to the luminosities of the remaining unidentified
hosts. We examine the nature of the host galaxy population and find that (1)
the UV luminosity distribution of GRB host galaxies is consistent with
expectations from a UV luminosity weighted random galaxy population with a
median luminosity of =0.1 L*; (2) there exists a moderate correlation
between UV luminosity and SiII 1526 absorption width, which together with the
observed large line widths of W(1526)>1.5 Ang for a large fraction of the
objects suggests a galactic outflow driven velocity field in the host galaxies;
(3) there is tentative evidence for a trend of declining ISM metallicity with
decreasing galaxy luminosity in the star-forming galaxy population at z=2-4;
(4) the interstellar UV radiation field is found ~ 35-350 times higher in GRB
hosts than the Galactic mean value; and (5) additional galaxies are found at <
2" from the GRB host in all fields with known presence of strong MgII
absorbers, but no additional faint galaxies are found at < 2" in fields without
strong MgII absorbers. Our study confirms that the GRB host galaxies (with
known optical afterglows) are representative of unobscured star-forming
galaxies at z>2, and demonstrates that high spatial resolution images are
necessary for an accurate identification of GRB host galaxies in the presence
of strong intervening absorbers.Comment: 24 emulateapj pages, 24 figures, ApJ in press; full-resolution
version available at http://lambda.uchicago.edu/public/tmp/ghost.pd
SAPS 3—From evaluation of the patient to evaluation of the intensive care unit. Part 1: Objectives, methods and cohort description
OBJECTIVE: Risk adjustment systems now in use were developed more than a decade ago and lack prognostic performance. Objective of the SAPS 3 study was to collect data about risk factors and outcomes in a heterogeneous cohort of intensive care unit (ICU) patients, in order to develop a new, improved model for risk adjustment. DESIGN: Prospective multicentre, multinational cohort study. PATIENTS AND SETTING: A total of 19,577 patients consecutively admitted to 307 ICUs from 14 October to 15 December 2002. MEASUREMENTS AND RESULTS: Data were collected at ICU admission, on days 1, 2 and 3, and the last day of the ICU stay. Data included sociodemographics, chronic conditions, diagnostic information, physiological derangement at ICU admission, number and severity of organ dysfunctions, length of ICU and hospital stay, and vital status at ICU and hospital discharge. Data reliability was tested with use of kappa statistics and intraclass-correlation coefficients, which were >0.85 for the majority of variables. Completeness of the data was also satisfactory, with 1 [0–3] SAPS II parameter missing per patient. Prognostic performance of the SAPS II was poor, with significant differences between observed and expected mortality rates for the overall cohort and four (of seven) defined regions, and poor calibration for most tested subgroups. CONCLUSIONS: The SAPS 3 study was able to provide a high-quality multinational database, reflecting heterogeneity of current ICU case-mix and typology. The poor performance of SAPS II in this cohort underscores the need for development of a new risk adjustment system for critically ill patients. ELECTRONIC SUPPLEMENTARY MATERIAL: Electronic supplementary material is included in the online fulltext version of this article and accessible for authorised users: http://dx.doi.org/10.1007/s00134-005-2762-
Galaxy Group at z=0.3 Associated with the Damped Lyman Alpha System Towards Quasar Q1127-145
(Abridged) We performed a spectroscopic galaxy survey, complete to m<20.3
(L_B>0.15L_B* at z=0.3), within 100x100" of the quasar Q1127-145 (z=1.18). The
VLT/UVES quasar spectrum contains three z<0.33 MgII absorption systems. We
obtained eight new galaxy redshifts, adding to the four previously known, and
galaxy star formation rates and metallicities were computed where possible. A
strong MgII system [W_r(2796)=1.8A], which is a known DLA, had three previously
identified galaxies; we found two additional galaxies associated with this
system. These five galaxies form a group with diverse properties, such as a
luminosity range of 0.04<L_B<0.63L_B*, an impact parameter range of 17<D<241kpc
and velocity dispersion of 115km/s. The DLA group galaxy redshifts span beyond
the 350km/s velocity spread of the metallic absorption lines of the DLA itself.
The two brightest group galaxies have SFRs of a few Msun/yr and should not have
strong winds. We have sufficient spectroscopic information to directly compare
three of the five group galaxies' (emission-line) metallicities with the DLA
(absorption) metallicity: the DLA metallicity is 1/10th solar, substantially
lower than the three galaxies' which range between less than 1/2 solar to solar
metallicity. HST/WFPC-2 imaging shows perturbed morphologies for the three
brightest group galaxies, with tidal tails extending 25kpc. We favor a scenario
where the DLA absorption originates from tidal debris in the group environment.
Another absorber exhibits weak MgII absorption [W_r(2796)=0.03A] and had a
previously identified galaxy at a similar redshift. We have identified a second
galaxy associated with this system. Both galaxies have solar metallicities and
unperturbed morphologies. The SFR of one galaxy is much lower than expected for
strong outflows. Finally, we have identified five galaxies at large impact
parameters with no associated MgII absorption.Comment: 15 pages, 7 figures, 5 tables. Accepted for publication in MNRAS
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