1,413 research outputs found
Sporadic Long-term Variability in Radio Activity from a Brown Dwarf
Radio activity has been observed in a large variety of stellar objects,
including in the last few years, ultra-cool dwarfs. To explore the extent of
long-term radio activity in ultra-cool dwarfs, we use data taken over an
extended period of 9 hr from the Very Large Array of the source 2MASS
J05233822-1403022 in September 2006, plus data taken in 2004. The observation
taken in September 2006 failed to detect any radio activity at 8.46 GHz. A
closer inspection of earlier data reveals that the source varied from a null
detection on 3 May 2004, to 95 Jy on 17 May 2004, to 230 Jy
on 18 June 2004. The lack of detection in September 2006 suggests at least a
factor of ten flux variability at 8.46 GHz. Three short photometric runs did
not reveal any optical variability. In addition to the observed pulsing nature
of the radio flux from another ultra-cool source, the present observations
suggests that ultra-cool dwarfs may not just be pulsing but can also display
long-term sporadic variability in their levels of quiescent radio emission. The
lack of optical photometric variability suggests an absence of large-scale
spots at the time of the latest VLA observations, although small very high
latitude spots combined with a low inclination could cause very low amplitude
rotational modulation which may not be measurable. We discuss this large
variability in the radio emission within the context of both gyrosynchrotron
emission and the electron-cyclotron maser, favoring the latter mechanism.Comment: 7 pages, 2 figures, 1 table, accepted for publication in A&A Letter
Designing for Collaborative Non-Driving-Related Activities in Future Cars:Fairness and Team Performance
With the gradual transition towards assisted and automated driving, the car will transform into a more social environment where passengers and drivers engage in Non-Driving-Related Activities (NDRA). To support collaboration among occupants in future vehicles, research suggests interactive systems controlled by several users at once. In this paper, we explore five concepts for the collaborative performance of NDRA with the use-case of music playlist creation. While prior work investigated the effect on social connectedness, we expand insights towards team performance and fairness. Results from a mixed-subject experiment (N=27) show that the concepts have major consequences on team performance and fairness. Certain concepts can promote or hinder coordination effectiveness and, in turn, impact intra-vehicular collaboration. Our observations also indicate that fairness is key to fostering social collaboration in AVs, while it does not naturally define a high team performance. Subsequently, we provide recommendations to guide future designs of collaborative NDRAs in vehicles.</p
High Resolution inline Topography of Iron in p-Doped Multicrystalline Bricks by MDP
AbstractThe iron density is one crucial parameter to verify the quality of the material. Brick measurements enable to check the material quality right at the beginning of the production line. This paper presents contact less high resolution inline topographic measurements of the iron density in multicrystalline silicon bricks by MDP (microwave detected photoconductivity). The measurement procedure is fully automatic and takes less than 5min a brick. The data obtained were compared to QSSPC (quasi steady state photoconductivity) measurements, however, with a loss in spatial resolution. Furthermore, passivated wafers were prepared from the bricks after the measurements and investigated individually. The consistency of all the data is remarkable
Empowering Driver-Passenger Collaboration: Designing In-Car Systems with a focus on Social Connectedness, Fairness, and Team Performance
Driving a car can be difficult when it comes to distractions caused by operating the in-vehicle infotainment system (IVIS). In-car passengers often help with performing IVIS-related tasks. However, an IVIS is often not designed with a focus on task collaboration. In this article, we focus on how to design in-car systems with the goal to support collaboration between a driver and a front-seat passenger. Based on infotainment-oriented tasks, we initially explore five key collaborative control concepts by means of an IVIS which differ from each other in terms of the number of available IVIS screens (one or two), access to menus (restricted and unrestricted), and the nature of performing tasks in parallel or one after the other. Results from a simulator study with N = 16 pairs show significant effects of the concepts on social collaboration in terms of perceived social connectedness (measured with sub-dimensions connectedness, affiliation, belongingness, companionship), team performance (coordination effectiveness and team cohesion), and fairness. We found that especially a dedicated passenger IVIS screen empowers front-seat passengers, reduces power dynamics, supports fairness, and minimizes driver distraction (caused by interacting passengers). We discuss the implications of these findings and posit recommendations to design future IVIS in passenger cars with improved driver-passenger collaboration by explicitly designing for balanced power roles, situational awareness, active communication, and a balance between drivers’ privacy and trust toward the passenger. Additionally, we outline a systematic overview of future work to explore the research field of driver-passenger collaboration in more breadth and depth.</p
A powerful bursting radio source towards the Galactic Centre
Transient astronomical sources are typically powered by compact objects and
usually signify highly explosive or dynamic events. While radio astronomy has
an impressive record of obtaining high time resolution observations, usually it
is achieved in quite narrow fields-of-view. Consequently, the dynamic radio sky
is poorly sampled, in contrast to the situation in the X- and gamma-ray bands
in which wide-field instruments routinely detect transient sources. Here we
report a new transient source, GCRT J1745-3009, detected in 2002 during a
moderately wide-field radio transient monitoring program of the Galactic center
(GC) region at 0.33 GHz. The characteristics of its bursts are unlike those
known for any other class of radio transient. If located in or near the GC, its
brightness temperature (~10^16 K) and the implied energy density within GCRT
J1745-3009 vastly exceeds that observed in most other classes of radio
astronomical sources, and is consistent with coherent emission processes rarely
observed. We conclude that GCRT J1745-3009 is the first member of a new class
of radio transient sources, the first of possibly many new classes to be
identified through current and upcoming radio surveys.Comment: 16 pages including 3 figures. Appears in Nature, 3 March 200
A Blind Search for Magnetospheric Emissions from Planetary Companions to Nearby Solar-type Stars
This paper reports a blind search for magnetospheric emissions from planets
around nearby stars. Young stars are likely to have much stronger stellar winds
than the Sun, and because planetary magnetospheric emissions are powered by
stellar winds, stronger stellar winds may enhance the radio luminosity of any
orbiting planets. Using various stellar catalogs, we selected nearby stars (<~
30 pc) with relatively young age estimates (< 3 Gyr). We constructed different
samples from the stellar catalogs, finding between 100 and several hundred
stars. We stacked images from the 74-MHz (4-m wavelength) VLA Low-frequency Sky
Survey (VLSS), obtaining 3\sigma limits on planetary emission in the stacked
images of between 10 and 33 mJy. These flux density limits correspond to
average planetary luminosities less than 5--10 x 10^{23} erg/s. Using recent
models for the scaling of stellar wind velocity, density, and magnetic field
with stellar age, we estimate scaling factors for the strength of stellar
winds, relative to the Sun, in our samples. The typical kinetic energy carried
by the stellar winds in our samples is 15--50 times larger than that of the
Sun, and the typical magnetic energy is 5--10 times larger. If we assume that
every star is orbited by a Jupiter-like planet with a luminosity larger than
that of the Jovian decametric radiation by the above factors, our limits on
planetary luminosities from the stacking analysis are likely to be a factor of
10--100 above what would be required to detect the planets in a statistical
sense. Similar statistical analyses with observations by future instruments,
such as the Low Frequency Array (LOFAR) and the Long Wavelength Array (LWA),
offer the promise of improvements by factors of 10--100.Comment: 11 pages; AASTeX; accepted for publication in A
Spin pumping and magnetization dynamics in metallic multilayers
We study the magnetization dynamics in thin ferromagnetic films and small
ferromagnetic particles in contact with paramagnetic conductors. A moving
magnetization vector causes \textquotedblleft pumping\textquotedblright of
spins into adjacent nonmagnetic layers. This spin transfer affects the
magnetization dynamics similar to the Landau-Lifshitz-Gilbert phenomenology.
The additional Gilbert damping is significant for small ferromagnets, when the
nonmagnetic layers efficiently relax the injected spins, but the effect is
reduced when a spin accumulation build-up in the normal metal opposes the spin
pumping. The damping enhancement is governed by (and, in turn, can be used to
measure) the mixing conductance or spin-torque parameter of the
ferromagnet--normal-metal interface. Our theoretical findings are confirmed by
agreement with recent experiments in a variety of multilayer systems.Comment: 10 pages, 6 figure
Measuring the Initial Mass Function of Low Mass Stars and Brown Dwarfs
I review efforts to determine the form and any lower limit to the initial
mass function in the Galactic disk, using observations of low-mass stars and
brown dwarfs in the field, young clusters and star forming regions. I focus on
the methodologies that have been used and the uncertainties that exist due to
observational limitations and to systematic uncertainties in calibrations and
theoretical models. I conclude that whilst it is possible that the low-mass
IMFs deduced from the field and most young clusters are similar, there are too
many problems to be sure; there are examples of low-mass cluster IMFs that
appear to be very discrepant and the IMFs for brown dwarfs in the field and
young clusters have yet to be reconciled convincingly.Comment: From a series of lectures presented at the Evry-Schatzman school on
Low-mass stars and the transition from stars to brown dwarfs, edited by C.
Charbonnel, C. Reyle, M. Schultheis. To appear in the EAS Conference Series.
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Computational strategies for dissecting the high-dimensional complexity of adaptive immune repertoires
The adaptive immune system recognizes antigens via an immense array of
antigen-binding antibodies and T-cell receptors, the immune repertoire. The
interrogation of immune repertoires is of high relevance for understanding the
adaptive immune response in disease and infection (e.g., autoimmunity, cancer,
HIV). Adaptive immune receptor repertoire sequencing (AIRR-seq) has driven the
quantitative and molecular-level profiling of immune repertoires thereby
revealing the high-dimensional complexity of the immune receptor sequence
landscape. Several methods for the computational and statistical analysis of
large-scale AIRR-seq data have been developed to resolve immune repertoire
complexity in order to understand the dynamics of adaptive immunity. Here, we
review the current research on (i) diversity, (ii) clustering and network,
(iii) phylogenetic and (iv) machine learning methods applied to dissect,
quantify and compare the architecture, evolution, and specificity of immune
repertoires. We summarize outstanding questions in computational immunology and
propose future directions for systems immunology towards coupling AIRR-seq with
the computational discovery of immunotherapeutics, vaccines, and
immunodiagnostics.Comment: 27 pages, 2 figure
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