377 research outputs found
Binarity in Cool Asymptotic Giant Branch Stars: A Galex Search for Ultraviolet Excesse
The search for binarity in AGB stars is of critical importance for our
understanding of how planetary nebulae acquire the dazzling variety of
aspherical shapes which characterises this class. However, detecting binary
companions in such stars has been severely hampered due to their extreme
luminosities and pulsations. We have carried out a small imaging survey of AGB
stars in ultraviolet light (using GALEX) where these cool objects are very
faint, in order to search for hotter companions. We report the discovery of
significant far-ultraviolet excesses towards nine of these stars. The
far-ultraviolet excess most likely results either directly from the presence of
a hot binary companion, or indirectly from a hot accretion disk around the
companion.Comment: revised for Astrophysical Journa
Stellar Activity in the Broad-Band Ultraviolet
The completion of the GALEX All-Sky Survey in the ultraviolet allows activity
measurements to be acquired for many more stars than is possible with the
limited sensitivity of ROSAT or the limited sky coverage of Chandra, XMM, or
spectroscopic surveys for line emission in the optical or ultraviolet. We have
explored the use of GALEX photometry as an activity indicator, using as a
calibration sample stars within 50 pc, representing the field, and in selected
nearby associations, representing the youngest stages of stellar evolution. We
present preliminary relations between UV flux and the optical activity
indicator R'_HK and between UV flux and age. We demonstrate that far-UV (FUV,
1350-1780{\AA}) excess flux is roughly proportional to R'_HK. We also detect a
correlation between near-UV (NUV, 1780-2830{\AA}) flux and activity or age, but
the effect is much more subtle, particularly for stars older than than ~0.5-1
Gyr. Both the FUV and NUV relations show large scatter, ~0.2 mag when
predicting UV flux, ~0.18 dex when predicting R'_HK, and ~0.4 dex when
predicting age. This scatter appears to be evenly split between observational
errors in current state-of-the-art data and long-term activity variability in
the sample stars.Comment: 37 pages, 12 figures. To appear in the Astronomical Journa
Control and Coordination in Hierarchical Systems
This book presents the applied theory of control and cooordination in hierarchical systems which are those where decision making has been divided in a certain way. It concentrates on various aspects of optimal control in large scale systems and covers a range of topics from multilevel methods for optimizing by interactive feedback procedures to methods for sequential, hierarchical control in large dynamic systems
Ultraviolet-Selected Field and Pre-Main-Sequence Stars Towards Taurus and Upper Scorpius
We have carried out a Galaxy Evolution Explorer (GALEX) Cycle 1 guest
investigator program covering 56 square degrees near the Taurus T association
and 12 square degrees along the northern edge of the Upper Scorpius OB
association. We combined photometry in the GALEX FUV and NUV bands with data
from the Two Micron All Sky Survey to identify candidate young (<100 Myr old)
stars as those with an ultraviolet excess relative to older main sequence
stars. Follow-up spectroscopy of a partial sample of these candidates suggest 5
new members of Taurus, with 8-20 expected from additional observations, and 5
new members of Upper Scorpius, with 3-6 expected from additional observations.
These candidate new members appear to represent a distributed, non-clustered
population in either region, although our sample statistics are as of yet too
poor to constrain the nature or extent of this population. Rather, our study
demonstrates the ability of GALEX observations to identify young stellar
populations distributed over a wide area of the sky. We also highlight the
necessity of a better understanding of the Galactic ultraviolet source
population to support similar investigations. In particular, we report a large
population of stars with an ultraviolet excess but no optical indicators of
stellar activity or accretion, and briefly argue against several
interpretations of these sources.Comment: 46 pages, 16 figures, 13 tables; Accepted to the Astronomical Journa
DNA-PAINT MINFLUX nanoscopy
MINimal fluorescence photon FLUXes (MINFLUX) nanoscopy, providing photon-efficient fluorophore localizations, has brought about three-dimensional resolution at nanometer scales. However, by using an intrinsic on–off switching process for single fluorophore separation, initial MINFLUX implementations have been limited to two color channels. Here we show that MINFLUX can be effectively combined with sequentially multiplexed DNA-based labeling (DNA-PAINT), expanding MINFLUX nanoscopy to multiple molecular targets. Our method is exemplified with three-color recordings of mitochondria in human cells
Performance of Sensitivity based NMPC Updates in Automotive Applications
In this work we consider a half car model which is subject to unknown but
measurable disturbances. To control this system, we impose a combination of
model predictive control without stabilizing terminal constraints or cost to
generate a nominal solution and sensitivity updates to handle the disturbances.
For this approach, stability of the resulting closed loop can be guaranteed
using a relaxed Lyapunov argument on the nominal system and Lipschitz
conditions on the open loop change of the optimal value function and the stage
costs. For the considered example, the proposed approach is realtime applicable
and corresponding results show significant performance improvements of the
updated solution with respect to comfort and handling properties.Comment: 6 pages, 2 figure
Aerosol Mixing State: Measurements, Modeling, and Impacts
Atmospheric aerosols are complex mixtures of different chemical species, and individual particles exist in many different shapes and morphologies. Together, these characteristics contribute to the aerosol mixing state. This review provides an overview of measurement techniques to probe aerosol mixing state, discusses how aerosol mixing state is represented in atmospheric models at different scales, and synthesizes our knowledge of aerosol mixing state’s impact on climate‐relevant properties, such as cloud condensation and ice nucleating particle concentrations, and aerosol optical properties. We present these findings within a framework that defines aerosol mixing state along with appropriate mixing state metrics to quantify it. Future research directions are identified, with a focus on the need for integrating mixing state measurements and modeling.Key PointsWe define aerosol mixing state and connect it to the physicochemical properties of aerosol particlesWe discuss existing measurements and models to understand chemical and physicochemical mixing stateWe explain the connection between aerosol mixing state and climate‐relevant aerosol propertiesPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/150540/1/rog20184_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/150540/2/rog20184.pd
Simple Behavior of Primary Cross Sections for Low Mass Particles in p-pbar Collisions at y=0 and sqrt(s)=1.8 TeV
A set of inclusive cross sections at zero rapidity is presented for p-pbar
interactions at center of mass energy sqrt(s)=1.8 TeV. Six particle cross
sections are corrected for secondary contributions from decays of higher mass
resonances in order to produce a set of primary cross sections. The primary
cross sections per spin state are well described by d(sigma^p)/dy|_(y=0)=
0.721*(pi*lambdabar_(pi)^2)*exp(-m/T), where m is the particle rest mass,
T=hbar*c/r_h, and r_h=0.97 fm. The deuterium production cross section is also
described if r_h is replaced by r_A=r_h*A^(1/3). The same exponential in m and
T describes primary charm fractions in e+e- collisions at least up to the J/Psi
mass. There is no significant evidence for strangeness or charm suppression if
only primary production of light hadrons is considered. There is evidence that
the primary cross section for each particle may have the same value for pp and
pbar-p collisions and that it may have nearly constant values between
sqrt(s)=63 GeV and sqrt(s)=1800 GeV. Fits to the final state transverse momenta
of the particles using a gas model favor a temperature T=132 MeV, a chemical
potential mu=129 MeV, and a transverse flow of the gas with beta_f=0.27.Comment: 20 pages, 18 figure
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