35,278 research outputs found
On-chip inverted emulsion method for fast giant vesicle production, handling, and analysis
Liposomes and giant unilamellar vesicles (GUVs) in particular are excellent compartments for constructing artificial cells. Traditionally, their use requires bench-top vesicle growth, followed by experimentation under a microscope. Such steps are time-consuming and can lead to loss of vesicles when they are transferred to an observation chamber. To overcome these issues, we present an integrated microfluidic chip which combines GUV formation, trapping, and multiple separate experiments in the same device. First, we optimized the buffer conditions to maximize both the yield and the subsequent trapping of the vesicles in micro-posts. Captured GUVs were monodisperse with specific size of 18 ± 4 µm in diameter. Next, we introduce a two-layer design with integrated valves which allows fast solution exchange in less than 20 s and on separate sub-populations of the trapped vesicles. We demonstrate that multiple experiments can be performed in a single chip with both membrane transport and permeabilization assays. In conclusion, we have developed a versatile all-in-one microfluidic chip with capabilities to produce and perform multiple experiments on a single batch of vesicles using low sample volumes. We expect this device will be highly advantageous for bottom-up synthetic biology where rapid encapsulation and visualization is required for enzymatic reactions
What is the Price of Hubris? Using Takeover Battles to Infer Overpayments and Synergies
We present a framework for determining the information that can be extracted from stock prices around takeover contests. In only two types of cases is it theoretically possible to use stock price movements to infer bidder overpayment and relative synergies. The takeover contest for Paramount in 1994 illustrates one of these generic cases. We estimate that Viacom, the winning' bidder, overpaid for Paramount by more than $2 billion. This occurred despite the fact that Viacom's CEO owned roughly 3/4 of Viacom. These results are consistent with managerial overconfidence and/or large private benefits, but not with the traditional agency-based incentive problem.
Age and Dust Degeneracy for Starburst Galaxies Solved?
A spectral evolution model of galaxies that includes both stellar and dust
effects is newly built. xApplying the model to 22 nearby starburst galaxies, we
have shown that far infrared luminosity of galaxies helps to break the
age-dustiness degeneracy. We have derived a unique solution of age and the
dustiness for each starburst galaxy. The resulting starburst ages and optical
depths are in the range and , respectively. The result is robust and is almost independent of model
assumptions such as dust distributions, extinction curves, and burst strengths.
With the rapidly growing sensitivity of submillimeter detectors, it should
become possible in the near future to determine the age and of
star-forming galaxies at redshifts and beyond. Accurate estimates
of for Lyman-break galaxies and high-z galaxies might require a
substantial revision of the previously claimed picture of star formation
history over the Hubble time.Comment: Latex (aas2pp4) 15 pages, 1 table, 6 figures. Accepted for Ap
Emission lines and optical continuum in low-luminosity radio galaxies
We present spectroscopic observations of a complete sub-sample of 13
low-luminosity radio galaxies selected from the 2Jy sample. The underlying
continuum in these sources is carefully modelled in order to make a much-needed
comparison between the emission line and continuum properties of FRIs with
those of other classes of radio sources. We find that 5 galaxies in the sample
show a measurable UV excess: 2 of the these sources are BL Lacs and in the
remaining 3 galaxies we argue that the most likely contributor to the UV excess
is a young stellar component. Excluding the BL Lacs, we therefore find that
\~30% of the sample show evidence for young stars, which is similar to the
results obtained for higher luminosity samples. We compare our results with
far-infrared measurements in order to investigate the far-infrared-starburst
link. The nature of the optical-radio correlations is investigated in light of
this new available data and, in contrast to previous studies, we find that the
FRI sources follow the correlations with a similar slope to that found for the
FRIIs. Finally, we compare the luminosity of the emission lines in the FRI and
BL Lac sources and find a significant difference in the [OIII] line
luminosities of the two groups. Our results are discussed in the context of the
unified schemes.Comment: 18 pages, 31 figures, MNRAS in press, (all enquiries to Clive
Tadhunter ([email protected])
Lagrange Model for the Chiral Optical Properties of Stereometamaterials
We employ a general Lagrange model to describe the chiral optical properties
of stereometamaterials. We derive the elliptical eigenstates of a twisted
stacked split-ring resonator, taking phase retardation into account. Through
this approach, we obtain a powerful Jones matrix formalism which can be used to
calculate the polarization rotation, ellipticity, and circular dichroism of
transmitted waves through stereometamaterials at any incident polarization. Our
experimental measurements agree well with our model.Comment: 10 pages, 3 figures, Theory and experimen
Cluster spacecraft observations of a ULF wave enhanced by Space Plasma Exploration by Active Radar (SPEAR)
Space Plasma Exploration by Active Radar (SPEAR) is a high-latitude ionospheric heating facility capable of exciting ULF waves on local magnetic field lines. We examine an interval from 1 February 2006 when SPEAR was transmitting a 1 Hz modulation signal with a 10 min on-off cycle. Ground magnetometer data indicated that SPEAR modulated currents in the local ionosphere at 1 Hz, and enhanced a natural field line resonance with a 10 min period. During this interval the Cluster spacecraft passed over the heater site. Signatures of the SPEAR-enhanced field line resonance were present in the magnetic field data measured by the magnetometer on-board Cluster-2. These are the first joint ground- and space-based detections of field line tagging by SPEAR
A BAYESIAN ANALYSIS OF THE AGES OF FOUR OPEN CLUSTERS
In this paper we apply a Bayesian technique to determine the best fit of stellar evolution models to find the main sequence turn off age and other cluster parameters of four intermediate-age open clusters: NGC 2360, NGC 2477, NGC 2660, and NGC 3960. Our algorithm utilizes a Markov chain Monte Carlo technique to fit these various parameters, objectively finding the best fit isochrone for each cluster. The result is a high precision isochrone fit. We compare these results with the those of traditional “by eye” isochrone fitting methods. By applying this Bayesian technique to NGC 2360, NGC 2477, NGC 2660, and NGC 3960 we determine the ages of these clusters to be 1.35 ± 0.05, 1.02 ± 0.02, 1.64 ± 0.04, and 0.860 ± 0.04 Gyr, respectively. The results of this paper continue our effort to determine cluster ages to higher precision than that offered by these traditional methods of isochrone fitting
Testing the photoionization models of powerful radio galaxies: Mixed line-emitting media in 3C 321
The photoionization models for the narrow emission line regions of powerful
radio galaxies have yet to be tested in depth. To this end, we present
high-quality long-slit spectroscopy of the powerful double-nucleus radio galaxy
3C 321. The data have good enough spatial resolution to be able to trace the
variation in emission-line properties on kpc scales. Continuum modelling and
subtraction enables the faint emission line fluxes to be measured in several
regions across the emission line nebula. We plot diagnostic line-ratio diagrams
and compare them with the predictions of various photoionization models,
finding that the data is best fit by models which assume a mixture of optically
thin and thick clouds illuminated by a power-law continuum.
The emission line kinematics, line ratios and deduced physical conditions
show remarkably little variation across the source. We deduce a mean electron
density of 400 +/- 120 cm-3 and a mean temperature of 11500 +/- 1500 K.
Assuming a single population of optically thick line-emitting clouds, we
calculate a mean photoionization parameter of (1.1 +/- 0.5) x 10e-2 and hence a
photoionizing photon luminosity of Q ~ 10e55 -- 10e56 photon/s/sr. This
indicates a central engine as luminous as that of the powerful quasar 3C 273,
yet there is no evidence for such an energetically prolific central engine at
either far-infrared or radio wavelengths. We therefore conclude that the
mixed-media models, which give Q ~ 5 x 10e53 -- 5 x 10e54, represent a more
likely scenario.
As a by-product of the continuum subtraction we infer that young stellar
populations account for ~ 0.4% of the visible stellar mass in the galaxy, and
that these populations are spatially extended.Comment: Accepted for publication in MNRA
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